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The skin microbiome is a dynamic ecosystem shaped by both internal and external factors. Ongoing research aims to distinguish natural fluctuations from those driven by environmental influences. What We Know: Facial skin is particularly sensitive to environmental factors like temperature, humidity and UV exposure, leading to variations in microbiome composition across different climates. For instance, UV radiation increases sebum production, promoting the growth of lipophilic microorganisms such as Cutibacterium acnes  and Malassezia , while warm temperatures (33.2–35.0°C) further support their growth by boosting sebum secretion. Higher humidity levels tend to enhance bacterial diversity (Tao et al., 2024). One study highlighted this variability, showing that individuals in northwest China’s dry, high-altitude regions had lower Malassezia  and bacterial diversity but higher ceramide and fatty acid levels compared to those living in the warm, humid southern regions (Tao et al., 2024). Industry Impact and Potential: A study tracking microbiome variability over the course of a year found that Cutibacterium  was more abundant in winter, correlating with increased transepidermal water loss (TEWL), a measure of skin barrier integrity. In contrast, Corynebacterium, Staphylococcus  and Streptococcus  were more abundant in summer. These changes in bacterial populations were linked to fluctuations in skin hydration, elasticity and TEWL (Seo et al., 2023). Interestingly, hydration levels did not show significant seasonal variation, but elasticity was higher in summer, aligning with the increased abundance of Staphylococcus  and Streptococcus . The study also revealed that TEWL was significantly higher in winter, while Cutibacterium  abundance and TEWL decreased from winter to summer (Seo et al., 2023). These findings highlight the importance of adapting skincare routines to seasonal changes to maintain microbiome health and barrier integrity. In colder months, increased TEWL from low humidity can be countered with hydrating products containing humectants like hyaluronic acid and barrier-strengthening ingredients like ceramides (Proksch, 2008). In warmer, humid conditions, lightweight, non-comedogenic products and consistent sunscreen use can manage oil levels while protecting against UV-induced microbiome shifts and barrier damage (Seo et al., 2023). Our Solution: At Sequential, we lead the way in microbiome research with a robust database of over 20,000 microbiome samples, 4,000 ingredients and a global network of 10,000 testing participants. Our solutions offer customisable microbiome studies and product formulations, with a focus on preserving microbiome integrity. Whether exploring the skin, scalp, oral or vulvar microbiome, Sequential is your ideal partner in advancing microbiome research. References: Proksch, E. (2008) Protection Against Dryness of Facial Skin: A Rational Approach. Skin Pharmacology and Physiology. 22 (1), 3–7. doi:10.1159/000159771. Seo, J.Y., You, S.W., Gu, K.-N., Kim, H., Shin, J.-G., Leem, S., Hwang, B.K., Kim, Y. & Kang, N.G. (2023) Longitudinal study of the interplay between the skin barrier and facial microbiome over 1 year. Frontiers in Microbiology. 14, 1298632. doi:10.3389/fmicb.2023.1298632. Tao, R., Li, T., Wang, Y., Wang, R., Li, R., Bianchi, P., Duplan, H., Zhang, Y., Li, H. & Wang, R. (2024) The facial microbiome and metabolome across different geographic regions. Microbiology Spectrum. 12 (1), e03248-23. doi:10.1128/spectrum.03248-23.

Introduction The vagina is one of the most heavily colonised organs of the human body, with a unique ecosystem consisting of bacteria, fungi, viruses and other groups of microorganisms that play a vital role in modulating reproductive fertility, preventing inflammatory diseases and sexually transmitted infections, and may even contain microbial biomarkers indicating risk of preterm delivery during pregnancy (Lee et al. , 2023). Its physical properties (i.e., low pH and oxygen) make it an ideal environment for specific colonisation by groups of mostly acid-favouring and low-oxygen tolerant species, resulting in a relatively low level of diversity (France et al. , 2022; Lee et al. , 2023).   In healthy, cisgender women (individuals whose gender identity is the same as their birth-assigned sex), the vaginal microbiomes is usually dominated by a single group of bacteria known as the Lactobacilli , which are capable of producing lactic acid compounds that work to maintain the acidic pH of the vagina and inhibit growth of harmful pathogens (Huang et al. , 2024). This low diversity composition is favoured within the vagina, as shifts from a Lactobacillus dominant to a more diverse microbiome are commonly associated with increased risk of disease and infection, including disorders such as sexually transmitted infections (STIs), bacterial vaginosis (BV), and even HIV (France et al. , 2022; Feil et al. , 2024). The vaginal microbiomes of transgender men Transgender men (i.e., individuals assigned female sex at birth but identify as male) who have retained their natal genitalia may also choose to undergo gender affirming hormone therapy (GAHT) in the form of testosterone supplementation to aid in presenting with a more masculine appearance through increased facial and body hair, greater muscle mass, and suppression of menstruation (Winston McPherson et al. , 2019).  While much of the focus of vaginal microbiome research has been related to cisgender women, it is also worth focusing on the properties of these communities in transgender individuals, especially those that might be undergoing testosterone therapy, as this hormone is predicted to play a strong role in influencing the composition of the vaginal microbiome with substantial effects. However, the relationship between the two remains to be fully explored, with only a couple of studies in the current literature seeking to understand it. Study No. 1: The vaginal microbiome of transgender men (Winston McPherson et al.,  2019) To better understand the effects of GAHT on vaginal microbiome composition, this study set out to investigate how testosterone would go on to influence the vaginal floras of a cohort of healthy transgender men prescribed testosterone for at least 1 year compared with samples taken from cisgender women, being one of the first studies in the field to do so (Winston McPherson  et al.,  2019). Results The researchers found the vaginal flora of most the transgender men to have a lower abundance of Lactobacillus (<2%) as the primary bacterial group inhabiting the vagina compared to the microbiomes of cisgender women (>90%), and a greater overall bacterial diversity and abundance of species such as Gardnerella  and Prevotella  associated with increased risk of bacterial vaginosis (BV).  However, transgender individuals receiving oestrogen either as a treatment for vaginal atrophy or BV showed a positive association with the majority presence of Lactobacillus  (>90%) and reduced species diversity in the microbiota, suggesting a similar effect of oestrogen in maintaining a favourable environment for Lactobacillus  colonisation and prevention of disease in transgender men. The authors go on to state that administration of intravaginal oestrogen might counteract these effects and restore balance to the vaginal microbiomes of transgender men receiving testosterone therapy (Winston McPherson  et al.,  2019). Conclusion Testosterone can act to cause compositional changes in the vaginal microflora of transgender individuals by depleting Lactobacillus  abundance and promoting the growth of bacterial species associated with bacterial vaginosis, leading to differences between cisgender women and transgender men. This study also draws a link between oestrogen and Lactobacillus , with the former promoting growth and colonisation of the vagina by the latter and reducing diversity, suggesting a possible therapy for the treatment of conditions associated with this kind of dysbiosis (Winston McPherson  et al.,  2019). Study No. 2: The vaginal microbiome of transgender men receiving gender-affirming hormonal therapy in comparison to that of cisgender women (Feil et al.,  2024) Building off results from previous studies, the aim of this was to investigate similarities between the vaginal microbiome compositions of transgender men and menopausal and premenopausal cisgender women as as the effects of hormonal testosterone therapy in the former and reduced oestrogen in the latter are believed to have a similar effects in both groups (Feil et al. , 2024). Results Analyses of microbiome composition revealed transgender men and menopausal women to possess greater species diversity than premenopausal women, with the vaginal communities of transgender men characterised by similarities to those of menopausal women, a reduction in Lactobacillus  and increase in the population of gut-associated species such as Campylobacter, Anaerococcus, Dialister, and Prevotella . However, the abundance of the latter two groups showed a decline over the duration of hormonal therapy in trans men. The authors of the study suggest these similarities between transgender men and menopausal women to be driven by a reduction of oestrogen in the blood resulting in a reduction of vaginal glycogen, a vital chemical metabolised by Lactobacillus species into lactic acid that maintains the ideal acidic environment of the vagina. As this oestrogen decreases, less glycogen is available as a food source for these beneficial bacteria, causing the population to decrease and the vaginal pH to rise as a result. This opens up room for colonisation by other species, thus causing the observed increase in species diversity, and increasing susceptibility to infection. Over time, the authors noted a reduction in this species diversity with length of testosterone treatment in transgender men, likely caused by a lowered abundance of Dialister and Prevotella  species, and suggesting a shift to a less diverse vaginal microbiome with prolonged testosterone therapy. Although they did note that Lactobacillus  populations failed to return to their original dominance even after this period (Feil et al. , 2024). Conclusion The study suggests that the reduced abundance of Lactobacillus  and overall increase in species diversity within the vaginal microbiomes of transgender men receiving GAHT to be driven by a reduction in glycogen compounds in the vagina that Lactobacillus  species use as a food source, with their subsequent loss opening up space for habitation by other species and infection, and resulting in effects similar to those in menopausal cisgender women while differing significantly from the microbiomes of premenopausal cisgender women (Feil et al. , 2024). Study No. 3: Characteristics of the Vaginal Microbiome Before and After Testosterone Treatment in Transgender Men (Panichaya et al.,  2024) Another study looking to investigate the effects of initiating testosterone therapy on the composition of vaginal microbiota in transgender men by comparing vaginal communities before and after testosterone use over the course of 12 weeks in a cohort of Thai participants, while also assessing its impact on the appearance of vulvovaginal symptoms such as vaginal pH, vaginal atrophy score (VAS), and vaginal maturation value (VMV) (Panichaya et al. , 2024). Results This study also reported a loss of Lactobacillus  dominance post-testosterone treatment, accompanied by a significant increase of Prevotella and Streptococcus . Similar to previous studies, administration of testosterone resulted in an increase in the vaginal microbiome diversity of transgender men in the post-treatment group, further lending support to the composition-altering effects of testosterone on these microbial communities.  Participants of the study reported the appearance of more vulvovaginal symptoms after 12 weeks of testosterone treatment, with higher VAS, higher vaginal pH, and worse VMVs, however these symptoms did not demonstrate any statistically significant correlation with the decreased relative abundance of Lactobacilli  observed in these groups, with the authors suggesting a potential trend that could be further elucidated through future studies with larger sample sizes. Interestingly, the study also failed to establish any significant statistical correlation between changes in hormone levels within the participants (i.e., decrease in estradiol/increase in testosterone) and reduction of Lactobacillus , another observation that merits being followed up on. While there were no reports of infection in the 12-week follow up after the study had ended, the authors predicted longer term use of testosterone might eventually cause vaginal infection and other physical symptoms (e.g., painful intercourse, itching, irregular bleeding) to emerge (Panichaya et al. , 2024). Conclusion This study demonstrated significant changes to occur in the vaginal microbiomes of transgender men undergoing testosterone therapy, including a reduction in the relative abundance of Lactobacillus  and increase in overall diversity, two symptoms commonly associated with potential adverse vaginal health outcomes. It also looked at physical effects resulting from hormonal therapy in relation to these compositional changes in the vaginal microbiota, and reported an interesting trend emerging between the two despite their lack of significant correlation (Panichaya et al. , 2024). Strengths & Limitations of Research Strengths : Improving our understanding of how testosterone therapy can influence the vaginal microbiomes of transgender men can drive the development of strategies to prevent or reduce the risk of serious infection or disease such as BV/HIV commonly associated with testosterone-altered microbial communities. This will aid in improving the quality of life and healthcare outcomes for transgender individuals undergoing GAHT, and also improve sexual health within this population. Developments in this field will also help destigmatize discussions and research surrounding vaginal health in transgender men so that individuals and healthcare professionals can accurately address concerns surrounding these topics, while also helping transgender individuals make more informed decisions regarding their health. Data from these studies can provide extensive repositories of vaginal and serum specimens collected from transgender participants that can be used by researchers as a resource to accelerate progress in fields such as disease research, drug development, and biomarker identification within the context of transgender health research (Muzny et al. , 2023). Limitations : The small sample sizes used in these studies reduces their ability to identify subtle differences between groups, draw clear correlations between hormone levels and vaginal microbiomes, while increasing the likelihood of obtaining statistical errors that could reduce the accuracy of conclusions being drawn from the data (Winston McPherson et al. , 2019). Many of the aforementioned studies also failed to collect any demographic information (race, ethnicity, or body mass index) on their participants, meaning little information could be obtained on the extent of these factors in influencing the rate or magnitude of testosterone-driven changes in vaginal microbiome composition (Winston McPherson et al. , 2019). More longitudinal studies looking into the effects of testosterone on the vaginal microflora of transgender men are needed. These will help better define the relationship between the two, and establish a stronger causal link between any observed compositional changes ( Lactobacillus  depletion; increase in diversity) and testosterone therapy, should one exist. Related Research and Future Directions The findings of these studies can be taken further through the development of therapeutic treatments to treat unwanted effects in the vaginal microbiomes of transgender individuals receiving GAHT, such as the use of vaginal or oral probiotics to prevent infection by restoring balance to the microbiome without the use of oestrogen therapy that can have potentially dysphoric effects (Feil et al. , 2024). Understanding the hormonal factors influencing the vaginal microbiome of transgender men may have potential therapeutic applications in developing approaches to restore microbiome balance in other groups. This may include those of menopausal women possessing similar compositions to transgender individuals, the neovaginal microbiomes of transgender women who have not yet started oestrogen therapy to establish these Lactobacillus  dominant communities, as well as cisgender women suffering from hormonal disorders such as polycystic ovary syndrome (PCOS) resulting in above average levels of testosterone that might cause similar microbiome shifts as those observed in transgender men. Gathering more demographic data (e.g., ethnicity/age/race) could help determine whether these factors affect how vaginal microbiomes respond to testosterone therapy and improve the generalisability of studies investigating testosterone’s influence on these microbial communities (Panichaya et al. , 2024). Conclusion The vagina is an incredibly complex organ housing trillions of microorganisms that play an essential role in its healthy development. However, many studies looking into the role of the vaginal microbiome have almost exclusively focused on these effects in cisgender women, with scarce information on how their role could be affected during gender-affirming testosterone therapy in transgender men. Despite this, recent findings suggest testosterone to be a big player in altering the composition of the vaginal microbiome from its healthy state of Lactobacillus  dominance to a more diverse one that runs the risk of causing infection or disease. More studies are needed to better understand this relationship, improve our knowledge of transgender health, and drive the development of effective treatments to minimise any risk of harm arising from these testosterone-mediated shifts in microbiome structure. References Feil, K. et al.  (2024) ‘The vaginal microbiome of transgender men receiving gender-affirming hormonal therapy in comparison to that of cisgender women’, Scientific Reports , 14(1), p. 21526. Available at:   https://doi.org/10.1038/s41598-024-72365-4 . France, M. et al.  (2022) ‘Towards a deeper understanding of the vaginal microbiota’, Nature Microbiology , 7(3), pp. 367–378. Available at:   https://doi.org/10.1038/s41564-022-01083-2 . Huang, L. et al.  (2024) ‘A multi-kingdom collection of 33,804 reference genomes for the human vaginal microbiome’, Nature Microbiology , 9(8), pp. 2185–2200. Available at:   https://doi.org/10.1038/s41564-024-01751-5 . Lee, C.Y. et al.  (2023) ‘New perspectives into the vaginal microbiome with systems biology’, Trends in Microbiology , 31(4), pp. 356–368. Available at:   https://doi.org/10.1016/j.tim.2022.09.011 . Muzny, C.A. et al.  (2023) ‘Impact of testosterone use on the vaginal microbiota of transgender men, including susceptibility to bacterial vaginosis: study protocol for a prospective, observational study’. Available at:   https://doi.org/10.1136/bmjopen-2023-073068 . Panichaya, P. et al.  (2024) ‘Characteristics of the Vaginal Microbiome Before and After Testosterone Treatment in Transgender Men’, Transgender Health  [Preprint]. Available at:   https://doi.org/10.1089/trgh.2023.0249 . Winston McPherson, G. et al.  (2019) ‘The Vaginal Microbiome of Transgender Men’, Clinical Chemistry , 65(1), pp. 199–207. Available at:   https://doi.org/10.1373/clinchem.2018.293654 .

The skin microbiome is vital for skin health and barrier integrity. Sun exposure, especially UV radiation, plays a significant role in modulating this ecosystem. While moderate sun exposure aids vitamin D synthesis, excessive UV radiation disrupts microbial balance, causing oxidative stress and altering microbial composition. Understanding the interaction between UV and the skin microbiome is crucial for advancing skincare and overall skin health. What we know: A significant shift in microbial beta diversity was observed on the forearms of participants after four weeks of extensive sun exposure compared to baseline, suggesting that sunlight alters the diversity and composition of the skin microbiota (Willmott et al ., 2023). An overall increase in Cyanobacteria , Fusobacteria , Verrucomicrobia , and Oxalobacteraceae  species was observed, while Lactobacillaceae  and Pseudomonadaceae  species showed a decline after UVR exposure (Gilaberte et al ., 2025). Research shows that bacteria, like skin cells, react differently to UVA and UVB light. One study found both UV types reduce Pseudomonas aeruginosa, but Escherichia coli was less affected by UVA, indicating varying bacterial responses to sunlight (Smith et al., 2023). A study found that SPF 20 sunscreen protects both skin and its microbiome, preventing erythema and preserving beneficial bacteria like Lactobacillus crispatus. In contrast, unprotected or placebo-treated skin showed a disrupted microbial balance, with a reduced Lactobacillus to Cutibacterium acnes ratio (Schuetz et al., 2024). Applying sunscreen prior to UV exposure helps support and protect the skin microbiome, and researchers suggest that using sunscreens with higher SPF levels could provide even stronger microbial and skin protection (Schuetz et al ., 2024). Industry impact and potential: The growing awareness of how sun exposure affects the skin microbiome is driving innovation in sun care. Research indicates that UV protection can influence the balance of skin microorganisms, paving the way for products that not only shield against sun damage but also support overall skin health. Further research is needed to understand how different UV wavelengths impact the skin microbiome and contribute to long-term skin health issues, including aging and chronic conditions. More studies are also required to evaluate how various sunscreen formulations affect the skin’s microbial balance (Gilaberte et al ., 2025). Our solution: At Sequential, we help skincare brands create sun care products that protect the microbiome and support skin health. Through in vivo testing and detailed analysis of formulations' impact on the skin’s microbial ecosystem, we ensure products deliver UV protection without disrupting microbial balance. With access to over 20,000 microbiome samples, we provide scientifically-backed solutions that meet the growing demand for skin care prioritizing long-term health and immediate benefits. References: Gilaberte Y, Piquero-Casals J, Schalka S, Leone G, Brown A, Trullàs C, Jourdan E, Lim HW,  Krutmann J, Passeron T. Exploring the impact of solar radiation on skin microbiome to develop improved photoprotection strategies. Photochem Photobiol. 2025 Jan-Feb;101(1):38-52. doi: 10.1111/php.13962. Epub 2024 May 20. PMID: 38767119; PMCID: PMC11737011. Schuetz R, Claypool J, Sfriso R, Vollhardt JH. Sunscreens can preserve human skin  microbiome upon erythemal UV exposure. Int J Cosmet Sci. 2024 Feb;46(1):71-84. doi: 10.1111/ics.12910. Epub 2023 Oct 6. PMID: 37664974. Smith, M. L., O’Neill, C. A., Dickinson, M. R., Chavan, B., & McBain, A. J. (2023). Exploring  associations between skin, the dermal microbiome, and ultraviolet radiation: advancing possibilities for next-generation sunscreens. Frontiers in Microbiomes , 2 , Article 1102315. https://doi.org/10.3389/frmbi.2023.1102315 Willmott T, Campbell PM, Griffiths CEM, O'Connor C, Bell M, Watson REB, McBain AJ,  Langton AK. Behaviour and sun exposure in holidaymakers alters skin microbiota composition and diversity. Front Aging. 2023 Aug 8;4:1217635. doi: 10.3389/fragi.2023.1217635. PMID: 37614517; PMCID: PMC10442491.

The relationship between our oral and gut microbiomes is a growing area of research, offering new insights into how these communities shape health and disease. Emerging evidence is revealing how everyday oral hygiene practices, like antibacterial mouthwash use, affect this balance. What We Know: The gut and oral microbiomes are among the body’s largest microbial ecosystems, comprising 29% and 26% of the total bacterial count, respectively. Despite their distinct environments, their two-way connection - the ‘oral-gut microbiome axis’ - facilitates the exchange of microbial signals and metabolites that influence digestion, immune responses and systemic health. Disruptions in this axis have been linked to gastrointestinal disorders, cardiovascular diseases, among others, underscoring its vital role in maintaining overall health (Carvalho et al., 2024).  Although these microbiomes are distinct - due to barriers like gastric acidity and bile - oral bacteria may sometimes bypass these defences and migrate to the gut, influencing the gut microbiome and potentially contributing to diseases such as inflammatory bowel disease (IBD), colorectal cancer and systemic inflammatory conditions (Kunath et al., 2024). Industry Impact and Potential: Prolonged use of antibacterial mouthwash has been shown to disrupt the oral microbiome. A study on Listerine Cool Mint found that daily use for three months increased levels of Fusobacterium nucleatum  and Streptococcus anginosus . These opportunistic bacteria are linked to periodontal disease, systemic illnesses and even oesophageal and colorectal cancers. Moreover, oral bacteria that bypass the gut’s barriers may trigger systemic inflammation, compromising immune function and contributing to chronic diseases (Laumen et al., 2024). Research on chlorhexidine mouthwash in mice revealed notable changes in gut health, including reduced microbiome diversity, impaired nutrient absorption, and altered metabolism. While outcomes like decreased weight gain may initially appear beneficial, they are likely a result of malabsorption, which can have harmful downstream effects (Carvalho et al., 2024). These findings highlight the need to explore the oral–gut microbiome axis further, particularly the role of the oral microbiome in gut function and nutrient absorption. This opens new possibilities for developing oral hygiene products that maintain oral microbiome integrity while safeguarding the gut microbiome, paving the way for innovative solutions that support holistic health. Our Solution: At Sequential, we lead microbiome product development and testing from our hubs in London, New York and Singapore. We help businesses create products that preserve microbiome integrity while achieving efficacy. Partner with us to develop cutting-edge oral hygiene solutions that target the oral-gut microbiome axis and advancing health outcomes. References: Carvalho, L.R.R.A., Boeder, A.M., Shimari, M., Kleschyov, A.L., Esberg, A., Johansson, I., Weitzberg, E., Lundberg, J.O. & Carlstrom, M. (2024) Antibacterial mouthwash alters gut microbiome, reducing nutrient absorption and fat accumulation in Western diet-fed mice. Scientific Reports. 14 (1), 4025. doi:10.1038/s41598-024-54068-y. Kunath, B.J., De Rudder, C., Laczny, C.C., Letellier, E. & Wilmes, P. (2024) The oral–gut microbiome axis in health and disease. Nature Reviews Microbiology. 22 (12), 791–805. doi:10.1038/s41579-024-01075-5. Laumen, J.G.E., Van Dijck, C., Manoharan-Basil, S.S., de Block, T., Abdellati, S., Xavier, B.B., Malhotra-Kumar, S. & Kenyon, C. (2024) The effect of daily usage of Listerine Cool Mint mouthwash on the oropharyngeal microbiome: a substudy of the PReGo trial. Journal of Medical Microbiology. 73 (6). doi:10.1099/jmm.0.001830.

Folliculitis decalvans (FD) is a rare and challenging type of alopecia that leads to hair follicle inflammation, resulting in hair loss and scarring. Recent research suggests that FD has a unique microbiological signature and is associated with an impaired immune response, opening new avenues for understanding and treating this condition. What We Know: FD typically presents as a slowly expanding, painful alopecic plaque on the vertex of the scalp, often in young males. Despite extensive research, the exact cause is unclear. However, several factors have been implicated, including genetic predisposition, Staphylococcus aureus  colonisation, bacterial biofilms, compromised epidermal barrier integrity, congenital abnormalities in follicular orifices and dysfunction in the local immune system (Moreno-Arrones et al., 2023). As there is no definitive cure for FD, the goal of treatment is to stabilise the disease. Current therapeutic options include topical and systemic corticosteroids, antibiotics and isotretinoin. Case reports also highlight unconventional therapies such as topical tacrolimus, photodynamic therapy (PDT), dapsone, intravenous immunoglobulin (IVIG) and TNFα inhibitors, though these treatments are supported by limited evidence (Rózsa et al., 2024). Interestingly, while S. aureus  colonisation has long been linked to FD, recent research suggests its role may have been overstated due to past limitations in microbiological techniques. New studies reveal that FD-affected hair follicles have a distinct microbiome, with key species including Ruminococcaceae, Agathobacter  sp., Tyzzerella  sp. and Bacteroidales vadin  HA21 (Moreno-Arrones et al., 2023). Additionally, FD patients show significantly lower levels of IL-10, TNF-α and IL-6 after exposure to bacterial strains, indicating an impaired immune response that could contribute to the disease (Moreno-Arrones et al., 2023). Industry Impact and Potential: A successful case study treated a therapy-resistant FD patient with CO2 laser-assisted PDT. PDT induces fibroblast apoptosis, generates reactive oxygen species and offers antimicrobial and anti-inflammatory effects. Applying CO2 laser before PDT enhances photosensitiser absorption by creating microscopic channels in the skin. This method, previously effective for hypertrophic acne scars (Rózsa et al., 2024). Our Solution: With over 20,000 microbiome samples and 4,000 ingredients in our extensive database, along with a global network of more than 10,000 testing participants, Sequential offers comprehensive services to assess the impact of products and formulations. Our commitment to preserving microbiome integrity makes us an ideal partner for developing scalp and hair care products, including those focused on FD and scarring treatments. References: Moreno-Arrones, O.M., Garcia-Hoz, C., Del Campo, R., Roy, G., Saceda-Corralo, D., Jimenez-Cauhe, J., Ponce-Alonso, M., Serrano-Villar, S., Jaen, P., Paoli, J. & Vano-Galvan, S. (2023) Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response. Dermatology (Basel, Switzerland). 239 (3), 454–461. doi:10.1159/000529301. Rózsa, P., Varga, E., Gyulai, R. & Kemény, L. (2024) Carbon-dioxide laser-associated PDT treatment of folliculitis decalvans. International Journal of Dermatology. 63 (9), 1256–1257. doi:10.1111/ijd.17136.

Menopause represents a significant hormonal shift, and its impact on the vaginal and vulvar microbiomes remains an area of emerging research. Given the prevalence of menopause-related conditions, understanding these changes is critical for advancing women's health and the treatment thereof. What We Know: Menopause introduces systemic symptoms and distinct changes in the vaginal microbiome, primarily driven by reduced estrogen levels. This reduction often leads to a decline in the dominant and favourable Lactobacillus  species, increasing the risk of microbial dysbiosis which is associated with further health complications including bacterial vaginosis, aerobic vaginitis, vulvovaginal candidiasis and increased risk of sexually transmitted infections (Muhleisen & Herbst-Kralovetz, 2016). Estrogen plays a vital role in regulating the vaginal microbiological environment by maintaining epithelial thickness and glycogen levels, promoting mucus secretion and lowering vaginal pH via Lactobacilli  colonisation and lactic acid production (Barrea et al., 2023) . These changes, along with shifts in the gut and oral microbiomes during menopause, are hypothesised to contribute to the development of menopause-related diseases, including osteoporosis, breast cancer, endometrial hyperplasia, periodontitis and cardiometabolic disorders. Therefore, interventions and solutions are crucial (Barrea et al., 2023) . Industry Impact and Potential: Hormone replacement therapy (HRT) has been shown to enhance Lactobacillus dominance in the vaginal microbiome, alleviating symptoms of dysbiosis. However, the negative side effects of HRT experienced by some patients mean that alternatives to this are necessary (Muhleisen & Herbst-Kralovetz, 2016) . Oral and vaginal probiotics hold great promise. Initial studies complement previous research findings on the menopause-vaginal microbiome connection, but additional trials are needed to determine the efficacy of bacterial therapeutics to modulate or restore vaginal homeostasis (Muhleisen & Herbst-Kralovetz, 2016) . In one study, a two-week oral supplementation with four Lactobacillus  species (two capsules daily) positively influenced vaginal microbiota colonisation in 22 postmenopausal patients undergoing chemotherapy for breast cancer. Although this is a small sample size, it highlights the potential of probiotic treatments (Marschalek et al., 2017) . Our Solution: In addition to vulvar microbiome analysis, we at Sequential provide services for assessing skin, scalp and oral microbiomes. We have established our company as a leader in facilitating the assessment and development of products that maintain microbiome integrity. Our team of experts is well-equipped to support your company in formulating innovative products and studies aimed at maintaining and improving the vulvar microbiome to support women’s health. References: Barrea, L., Verde, L., Auriemma, R.S., Vetrani, C., Cataldi, M., Frias-Toral, E., Pugliese, G., Camajani, E., Savastano, S., Colao, A. & Muscogiuri, G. (2023) Probiotics and Prebiotics: Any Role in Menopause-Related Diseases? Current Nutrition Reports. 12 (1), 83–97. doi:10.1007/s13668-023-00462-3. Marschalek, J., Farr, A., Marschalek, M.-L., Domig, K.J., Kneifel, W., Singer, C.F., Kiss, H. & Petricevic, L. (2017) Influence of Orally Administered Probiotic Lactobacillus Strains on Vaginal Microbiota in Women with Breast Cancer during Chemotherapy: A Randomized Placebo-Controlled Double-Blinded Pilot Study. Breast Care (Basel, Switzerland). 12 (5), 335–339. doi:10.1159/000478994. Muhleisen, A.L. & Herbst-Kralovetz, M.M. (2016) Menopause and the vaginal microbiome. Maturitas. 91, 42–50. doi:10.1016/j.maturitas.2016.05.015.

The vaginal microbiome undergoes profound changes during pregnancy, marked by shifts in microbial composition and diversity that significantly impact maternal health. While the importance of these shifts is increasingly recognised, the tools to interpret these changes remain limited. What We Know: The vaginal microbiome plays a pivotal role in pregnancy, with a healthy state predominantly featuring Lactobacillus  species. These bacteria help maintain a low pH, protecting against infections. Microbial dysbiosis is linked to complications such as preterm birth (PTB), miscarriage, gestational diabetes mellitus (GDM), preeclampsia and chorioamnionitis (CAT) (Gerede et al., 2024) . PTB is associated with increased levels of anaerobic bacteria like Gardnerella vaginalis and Prevotella . Communities dominated by L. iners  or anaerobic bacteria carry higher risks compared to  L. crispatus -dominant profiles. Similarly, miscarriage often correlates with reduced Lactobacillus  abundance and greater microbial diversity. Dysbiosis not only disrupts the protective functions of the microbiome but also promotes inflammation and tissue damage, which can contribute to complications such as cervical insufficiency or placental ischemia (Gerede et al., 2024) . In GDM, altered microbiota may exacerbate inflammatory pathways, worsening glucose intolerance. Elevated levels of Prevotella bivia  have been implicated in inflammation associated with preeclampsia, while a diverse microbiome depleted of L. crispatus  is linked to increased infection risks in CAT. These microbial shifts reflect dynamic interactions with maternal physiology and evolve across pregnancy trimesters (Parraga-Leo et al., 2024) . Industry Impact and Potential: Probiotic interventions to restore Lactobacillus  dominance show promise for managing bacterial vaginosis, but their efficacy in preventing broader pregnancy complications warrants further investigation. New evidence suggests that microbial profiles and community disruptions could serve as biomarkers for identifying high-risk pregnancies (Parraga-Leo et al., 2024). Recent innovations include the Vaginal Microbiome Atlas during Pregnancy (VMAP), which integrates data from 11 studies and 3880 samples across 1402 individuals. This comprehensive resource leverages MaLiAmPi, a cutting-edge phylogenetic tool implemented via a Nextflow pipeline, to harmonise diverse datasets. By addressing technical variations and improving accuracy, MaLiAmPi enhances the reliability of microbiome data, setting a new standard for microbiome analysis (Parraga-Leo et al., 2024). Our Solution: Sequential specialises in microbiome analysis, offering services for assessing the vulvar microbiome alongside skin, scalp and oral microbiomes. Our expertise in developing products that maintain microbiome integrity positions us as industry leaders in supporting innovations for women’s health.  References: Gerede, A., Nikolettos, K., Vavoulidis, E., Margioula-Siarkou, C., Petousis, S., Giourga, M., Fotinopoulos, P., Salagianni, M., Stavros, S., Dinas, K., Nikolettos, N. & Domali, E. (2024) Vaginal Microbiome and Pregnancy Complications: A Review. Journal of Clinical Medicine. 13 (13), 3875. doi:10.3390/jcm13133875. Parraga-Leo, A., Oskotsky, T.T., Oskotsky, B., Wibrand, C., Roldan, A., et al. (2024) VMAP: Vaginal Microbiome Atlas during Pregnancy. JAMIA open. 7 (3), ooae099. doi:10.1093/jamiaopen/ooae099.

Introduction The human microbiome is a significant driver of human health and disease, composed of trillions of microorganisms that contribute to supporting host health and development. While various factors play a role in influencing the overall diversity and composition of these communities, little remains known regarding the driving factors determining their inheritance and establishment (Benga et al. , 2024). Two main competing hypotheses exist to explain this: either the human microbiome is actively shaped by (1) host genetics, or (2) maternal transmission. Many studies seeking to resolve them have achieved mixed results, making it difficult to conclude on which is the primary driver of microbial inheritance. Regardless, recent findings on the skin and gut microbiomes now suggest that host genotype might play a more important role in the active shaping of certain microbial communities than initially thought (Benga et al. , 2024). Importance of the skin and gut microbiomes As the largest organ of the human body, the skin employs a variety of chemical, physical, and biological defences to protect the body from external stress or damage by acting as a barrier to infection, promoting thermoregulation, and preventing water loss (Smythe and Wilkinson, 2023). As an extra layer of protection, it has also evolved a specialised community of symbiotic microorganisms to carry out additional functions pertaining to human skin health known as the skin microbiome. With a density of 104  to 106 bacteria per square centimetre of skin surface (Cundell, 2018), it plays an essential role in promoting skin health by preventing growth of pathogens, priming the immune system to differentiate harmful microbes from friendly ones (Lunjani et al. , 2021), and even regulating skin growth and development (Meisel et al. , 2018). The gut is another key organ that possesses its own highly diverse and interconnected community of microorganisms, reaching densities as high as 1012 cells per gram depending on segment (Sekirov et al. , 2010). These microbes line the inner walls of the gastrointestinal tract like the stomach, small, and large intestine, where they aid in carrying out essential functions involving development of the human nervous (Dash, Syed and Khan, 2022) and immune systems, influencing host metabolic activity, fermenting food, and defending against pathogens (Hou et al. , 2022).  Influence of host genotype Several factors influence human microbiome composition over the course of an individual’s life. In most cases, these forces can act to introduce new species, increase or decrease their abundance, or completely wipe them out, which can affect host health in either a positive or negative direction. While we have a fairly comprehensive understanding of the environmental and endogenous factors modulating gut (e.g., immune system, diet) and skin (e.g., cosmetics, hormones) microbiome composition, less is known regarding the key factors influencing the active shaping of these communities in early life. So far two possible hypotheses have been proposed: (1) host genetics actively shape the microbiome, or (2) microbial inheritance occurs through maternal transmission.  Evidence that all humans (to date) share over 50 bacterial species across their gut microbiota despite other compositional differences is taken as evidence that there exists a core human gut metagenome responsible for preserving these groups across the human population (Boccuto et al. , 2023). Host-genetics are theorised to influence establishment of the gut microbiome through specific genes. Although the mechanisms of how it does so is not so well understood, some evidence points to these genes influencing certain physiological factors in the host body that affect gut landscape and resulting growth of microbes. For example, one study reported a strong association between the lactase gene and levels of Bifidobacterium , a bacterium that has evolved to digest sugars found in human and cow milk, with lactose-intolerant individuals possessing a higher abundance of this bacteria than lactose-persisters (Qin et al. , 2022). This is thought to be because their inability to metabolise lactose makes this sugar more easily available for consumption by bacteria in the gut compared to persisters that can break it down on their own, thus increasing their population (Goodrich et al. , 2016). As with the gut, microbial communities on the skin are thought to be influenced at some level by host genetic factors, albeit if similarly (if not more) understudied, with studies pointing to the influence of these genes on skin architecture (Si et al. , 2015) and its associated immune system (Srinivas et al. , 2013) affecting the ability of certain species to colonise the skin surface. For example, one study found a significant link between genetic variants related to deficient skin barrier function and an abundance of Corynebacterium jeikeium , a skin bacterium responsible for causing infection in immunocompromised patients, suggesting an impaired skin barrier results in poorer defence against pathogenic bacteria like C. jeikeium  that permit it to invade and cause disease more easily (Si et al. , 2015). Influence of maternal transmission Other sources point to the early establishment of an individual’s gut microbiota being primarily driven by maternal inheritance, with mode of delivery (vaginal or caesarean) being the main mechanism through which this occurs, however, the extent of its influence over the gut microbiome remains controversial. Some studies state vaginally-delivered infants possess more species characteristic of the mother’s vaginal ( Lactobacillus + Bacteroides ) and fecal microbiota ( Bifidobacterium ), while those delivered via C-section have a greater abundance of skin microbes such as Staphylococcus  (Wang et al. , 2024). However, these findings are inconsistent across studies, and some even suggest these effects are short-lived, with compositional differences between the two groups dropping to <2% within 5 years of an infant’s life (Bogaert et al. , 2023). Other proposed means by which maternal legacy shapes the gut microbiome is through breastfeeding, which transfers essential nutrients and beneficial microbes from the mother’s milk microbiome to the infant gut (Tian et al. , 2023), or placental transmission (Miko et al. , 2022) of microbes and microbial metabolites from the mother’s gut to the infant’s to seed the gut and prime the fetus’s primitive immune system to distinguish between friendly and harmful microbe strains. Similarly, mode of delivery has also been found to play a role in influencing the establishment of bacterial and fungal communities present on the infant skin, with one study reporting vaginally-born children possess more vagina-associated fungal groups ( Candida  and Rhodotorula ) than caesarean-delivered children that possess more skin-associated and airborne fungal genera ( Malassezia  and Alternaria ) (Wang et al. , 2022). Other studies have also reported differences in the bacterial composition of vaginally and caesarean-delivered children, with the former possessing more vaginal bacteria like Lactobacillus , and latter a greater abundance of skin bacteria, like  Staphylococcus, Corynebacterium , and Cutibacterium , indicating some level of influence in delivery mode in influencing skin microbiome abundance for the first 10 years of life (Dominguez-Bello et al. , 2010). Other studies however, have noted that microbial richness, diversity, or taxonomic profiles do not significantly differ between the cutaneous microbiomes of the two infant groups in the four weeks after birth (Pammi et al. , 2017), or even between vaginally and caesarean-delivered infants aged 1–3 months (Capone et al. , 2011). These observations are believed to be attributed to the highly dynamic nature of the newborn skin microbiome that resolves these differences over time, and also highlight the inconclusive nature of this data. Study: The host genotype actively shapes its microbiome across generations in laboratory mice (Benga et al.,  2024) Existing literature regarding the effects of maternal legacy (i.e., passage through the birth canal, weaning, coprophagy, and grooming) and host genotype on human microbiomes remain inconclusive. This study set out to determine which of the two factors plays a more important role in actively shaping host microbiome composition over several generations within a controlled setting, being one of the first studies to both look at host genotype effects on skin-based communities, and maternal effects across multiple generations, providing greater insight into its longer-term influences (Benga et al. , 2024).  Results The team collected early-stage embryos from two different mice strains, and by carefully controlling the environment to minimise its effect on the mice, bred them for six generations. The first generation of offspring were exposed to a common initial microbiome to observe how the effects of host genetics and maternal legacy would go on to alter composition over the next five generations, and disentangle these factors (Benga et al. , 2024). Figure 1: Schematic representation of microbiome inheritance across six generations of mice. (1) The study investigates whether microbiome composition is primarily shaped by maternal transmission or host genetics. (2) In early generations, maternal legacy plays a dominant role in microbiome composition. (3) Over successive generations, the influence of maternal transmission diminishes, and host genotype becomes the primary factor shaping microbiome structure, as indicated by the balance shifting from maternal legacy (blue) to host genotype (yellow) in later generations. Image taken from   (Benga et al., 2024). As illustrated in Figure 1, maternal legacy had a strong effect in shaping microbiome composition within the first generation of offspring, particularly for gut-based communities. However, its influence over both skin and gut microbiome composition weakened over time and was gradually overpowered by host genotype across subsequent generations. By F3 to F5, genetic factors became the dominant force in determining microbiome structure, as represented by the shifting balance in the schematic diagram. The study identified 33 microbial species that preferentially colonized hosts of specific genetic backgrounds, indicating genotype-specific enrichment of particular taxa. Furthermore, quantification of blood serum metabolites revealed significant differences in microbial metabolite abundance between host genotypes, suggesting an interaction between host genetics and microbiome function (Benga et al. , 2024). Conclusion The study suggests that under controlled environments, host genetic traits far outweigh any maternal impact on the gut microbiome, with genotype driving the active shaping of the host microbiome over several generations under controlled environmental factors. These effects could also possibly extend to the metabolic activity of the microbiome being modulated by host genetic factors, thus further shaping its behaviour and function. The study resolves the debate by showing that maternal legacy does not persist beyond the initial offspring generation in stable environments. This study by Benga et al. (2024) stands out as one of the few researches to explore both the effects of host genotype and the maternal influences on the microbiome. However, it is essential to acknowledge that findings from mice models may not fully translate to human physiology. Therefore, future studies should aim to replicate this research in human populations to better understand how host genotype and maternal effects interact to shape the microbiome.  Strengths and limitations Strengths: Improving our understanding of the factors modulating the composition and behaviour of the human microbiome has important implications for the identification of host disease markers and abnormal species growth that can interfere with microbiome function to cause disease, allowing the development of measures that mitigate against these host genotype-driven effects (Benga et al. , 2024) Understanding the factors influencing infant microbiomes and their role in the subsequent development of early immunity can catalyse the development of novel prebiotic/probiotic therapies that prevent pathogen colonisation and infection in vulnerable infant populations (Pammi et al. , 2017) Developing multi omic platforms that can analyse the metagenomic composition of individuals in relation to other components such as proteomics and metabolomics can help identify any genetic markers that could be associated with a dysbiotic microbiota and offer personalised solutions to help counteract and balance these effects  Limitations: Many of the studies looking into disentangling the effects of maternal and host genetic influence on microbiome composition remain inconclusive regarding the effects of either, with many studies concluding on the influence of host genotype being performed on immune defective or highly inbred mice, or lacking natural process of microbiome colonisation, instead relying on artificial methods not representative of actual microbial exposure in human infants (Benga et al. , 2024) These studies also fail to consider sites other than the gut microbiome, leaving a scarcity of information regarding the influence of maternal and host-specific factors on other communities in the body such as the skin, thus preventing any meaningful conclusions being drawn from gut-specific studies More longitudinal studies are needed to establish a stronger long-term link between these factors and their influence on human microbiomes, with most host genotype studies using murine models that may not accurately reflect human physiology, behaviours, and life history processes/child-rearing practices Implications & Applications Development of therapies to maintain the health of the microbiome in susceptible populations or reverse the dysbiotic effect of faulty genetics Knowledge of how maternal influence can affect microbiome and resulting infant health can empower caregivers to practice microbiome-friendly child rearing where possible, or encourage the development of similarly beneficial alternatives if not Combining genetics and microbiome screening approaches can allow for more accurate models to be drawn to predict individual therapeutic drug responses when treating dysbiotic microbiomes (Sanna et al. , 2022) Related Research and Future Directions Application of experiments seeking to establish a more causal relationship between host genotype and microbiome composition via studies implementing controlled interventions (e.g., genetic knock-outs, germ-free hosts) to better understand the genetic mechanisms controlling microbiome composition (Bubier, Chesler and Weinstock, 2021) Expanding upon the respective roles of maternal legacy and host genotype in influencing microbiome composition and shaping at other body sites such as the vaginal and oral microbiomes to understand how these can influence overall health and disease progression Extend this to see how host genotype can influence the relationship between microbiome dysbiosis and psychological health by studying the relationship between host genetics, microbiome composition, and any psychiatric disorder-associated phenotypes or endophenotypes Conclusion The skin and gut both harbour trillions of microbes that play a crucial role in the maintenance of health and regular bodily function, with numerous factors contributing to their composition. Host genotype is likely to prevail over the effects of maternal legacy when determining the initial formation and establishment of these microbial communities in early life, with maternal legacy effects only persisting in a single generation, after which they are overpowered and persisted by the host’s own genetic factors. Expanding these studies to other bodily sites, and more longitudinal ones, can help elucidate the extent to which these factors persist in their influence, as well as how they interact with or drive disease phenotypes (Benga et al. , 2024). At Sequential, we are at the forefront of microbiome research, revolutionizing the field through its innovative Multi-Omic Studies, which integrate human and microbiome analysis to uncover deeper insights into biological interactions. 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Eczema, or atopic dermatitis (AD), is a chronic inflammatory skin condition marked by skin barrier dysfunction and immune dysregulation. Driven by genetic, immunological and environmental factors, as well as skin microbiome changes, emerging research suggests live biotherapeutic products (LBPs) could revolutionise its treatment and prevention. What We Know: During AD flare-ups, microbial diversity declines and Staphylococcus aureus  often dominates. Up to 70% of individuals with AD have S. aureus  colonisation on lesional skin and 30%–40% on non-lesional skin. A disrupted skin barrier, due to genetic and environmental factors, increases pH and water loss, creating conditions for S. aureus overgrowth (Totté et al., 2016). The severity of AD symptoms correlates with S. aureus  levels, exacerbated by toxins like δ-toxin and PSMα. Notably, many AD patients’ microbiomes lack gram-negative bacteria, further reducing microbial diversity (Locker et al., 2024). LBPs, defined as live organisms used to prevent, treat, or cure diseases, offer a novel approach to addressing these imbalances (Ağagündüz et al., 2022). Industry Impact and Potential: LBPs show promise by targeting S. aureus  overgrowth and improving skin health. Examples include Roseomonas mucosa  and coagulase-negative staphylococci (e.g., Staphylococcus hominis  A9), which reduce S. aureus  through antimicrobial and immune-modulating mechanisms. Furthermore, Nitrosomonas eutropha  B244 produces anti-inflammatory nitrite, showing potential to alleviate AD  symptoms(Locker et al., 2024). @Concerto Bioscience recently initiated a Phase 1 trial of Ensemble No.2 (ENS-002), a topical LBP targeting S. aureus overgrowth. ENS-002 employs three microbial strains to address the root microbial deficiencies linked to AD. Designed for topical application, it minimises systemic risks like immune suppression or infections (Andrus, 2024). ENS-002’s development leveraged Concerto's kChip screening technology, which tests millions of microbial combinations to uncover interactions that modulate skin health. Using kChip, over 6 million microbial communities were screened to identify the "ensemble" of bacteria that neutralises pathogenic S. aureus. Our Solution: At Sequential, we specialise in Microbiome Product Testing to support your business’ goals, such as innovative AD treatments. Our tailored studies and product formulation support ensure developments that maintain microbiome integrity, promoting efficacy, compatibility, and healthier skin. Partner with us to confidently develop microbiome-based topical solutions that address AD’s unique challenges. References: Ağagündüz, D., Gençer Bingöl, F., Çelik, E., Cemali, Ö., Özenir, Ç., Özoğul, F. & Capasso, R. (2022) Recent developments in the probiotics as live biotherapeutic products (LBPs) as modulators of gut brain axis related neurological conditions. Journal of Translational Medicine. 20 (1), 460. doi:10.1186/s12967-022-03609-y. Andrus, E. (2024) Concerto Biosciences Announces First Participant Dosed with Live Biotherapeutic ENS-002 in Phase 1 Trial for Atopic Dermatitis. 2024. Concerto Biosciences. https://www.concertobio.com/press/concerto-biosciences-announces-first-participant-dosed-with-live-biotherapeutic-ens-002-in-phase-1-trial-for-atopic-dermatitis [Accessed: 19 November 2024]. Locker, J., Serrage, H.J., Ledder, R.G., Deshmukh, S., O’Neill, C.A. & McBain, A.J. (2024) Microbiological insights and dermatological applications of live biotherapeutic products. Journal of Applied Microbiology. 135 (8), lxae181. doi:10.1093/jambio/lxae181. Totté, J.E.E., van der Feltz, W.T., Hennekam, M., van Belkum, A., van Zuuren, E.J. & Pasmans, S.G.M.A. (2016) Prevalence and odds of Staphylococcus aureus carriage in atopic dermatitis: a systematic review and meta‐analysis. British Journal of Dermatology. 175 (4), 687–695. doi:10.1111/bjd.14566.

The ‘exposome’ refers to the complex interplay of environmental exposures that influence the skin over a lifetime, including factors such as pollution, UV radiation and lifestyle choices. Comparable in complexity to the skin microbiome, the exposome represents an exciting frontier in research, with significant implications for skincare innovation and personalised solutions. What We Know: The exposome encompasses a broad range of environmental and lifestyle factors: air pollution, UV radiation, climate, diet, sleep patterns, stress and hormonal changes. Each individual’s exposome is unique, shaped by the combination of these factors over time (Passeron et al., 2020). Key environmental elements such as traffic-related air pollution, hormones, nutrition, stress and sleep significantly impact skin ageing and overall skin health. For example, pollution accelerates pigmentation, wrinkles and eczema, while hormonal fluctuations, poor nutrition and stress contribute to inflammation, collagen degradation and conditions like atopic dermatitis, psoriasis and acne. These factors affect biochemical processes that influence skin ageing and the development of inflammatory skin disorders (Passeron et al., 2020). However, the skin’s exposome has been relatively underexplored and further investigation is needed to understand how these factors interact and the net effects they have on the skin (Krutmann et al., 2017). Industry Impact and Potential: As research into the exposome evolves, the skincare industry is increasingly focusing on how these factors drive skin ageing and health, leading to more personalised, targeted skincare solutions. One framework, called The Skin Interactome, integrates the genome, microbiome and exposome to unravel the molecular mechanisms underlying skin health and ageing (Khmaladze et al., 2020). This holistic approach examines how genetic, environmental and microbial factors work together to influence skin physiology. By identifying key molecular pathways, such as those involved in collagen synthesis, this framework aims to develop targeted strategies to protect skin health and delay the visible signs of ageing (Khmaladze et al., 2020). Pooling research across these distinct areas of skincare is vital, as it provides a comprehensive understanding of how environmental, lifestyle and biological factors collectively influence skin health and ageing. This integrated approach allows for the development of more targeted and effective skincare solutions. Our Solution: Sequential is at the forefront of microbiome research, supported by a database of 20,000 microbiome samples, 4,000 ingredients and a global network of 10,000 testing participants. Our customisable solutions span microbiome studies and product formulation, with a strong focus on preserving biome integrity. Whether exploring the skin, scalp, oral or vulvar microbiome, we are your ideal partner for advancing research. References: Khmaladze, I., Leonardi, M., Fabre, S., Messaraa, C. & Mavon, A. (2020) The Skin Interactome: A Holistic ‘Genome-Microbiome-Exposome’ Approach to Understand and Modulate Skin Health and Aging. Clinical, Cosmetic and Investigational Dermatology. 13, 1021–1040. doi:10.2147/CCID.S239367. Krutmann, J., Bouloc, A., Sore, G., Bernard, B.A. & Passeron, T. (2017) The skin aging exposome. Journal of Dermatological Science. 85 (3), 152–161. doi:10.1016/j.jdermsci.2016.09.015. Passeron, T., Krutmann, J., Andersen, M.L., Katta, R. & Zouboulis, C.C. (2020) Clinical and biological impact of the exposome on the skin. Journal of the European Academy of Dermatology and Venereology: JEADV. 34 Suppl 4, 4–25. doi:10.1111/jdv.16614.

Scalp psoriasis is a common yet often treatment-resistant autoimmune condition that frequently co-occurs with psoriasis in other areas. Currently, the specific influence of the scalp microbiome on scalp psoriasis, and how this can be leveraged for treatment, remains largely unexplored. What We Know: Psoriasis is a chronic inflammatory skin condition affecting 1–3% of the global population, characterised by persistent, scaly plaques. Genetic, environmental and epigenetic factors contribute to its development, with up to 80% of psoriasis patients experiencing scalp involvement (Choi et al., 2024).  Treatments for scalp psoriasis range from topical agents, including steroids and vitamin D analogues, to systemic treatments like methotrexate and cyclosporine. Despite available therapies, managing scalp psoriasis remains complex due to challenges with topical application and variability in patient response (Ghafoor et al., 2022) . Industry Impact and Potential: The skin microbiome of psoriasis patients differs significantly from that of healthy individuals. Psoriatic lesions exhibit increased Staphylococcus  and decreased Cutibacterium  compared to healthy controls. This dysbiosis may cause inflammation, impaired skin barrier functions and autoimmunity (Choi et al., 2024) . Researcher has shown that microbial diversity in the scalp microbiome increased with the severity of scalp psoriasis. Pseudomonas  and Malassezia  species, particularly M. globosa , were more prevalent in severe cases. Malassezia  is linked to several skin conditions, including psoriasis and its lipase activity may disrupt the skin barrier and provoke inflammation (Choi et al., 2024) .  Additionally, the IL-17 pathway, a key player in psoriasis pathogenesis, interacts with Malassezia  to exacerbate skin inflammation. Understanding these microbial changes offers a promising avenue for developing targeted treatments that address the root causes of scalp psoriasis, potentially enhancing patient outcomes (Choi et al., 2024) .  Powered by their Amino M³ Complex,™ @Act + Acre’s Microbiome Cooling Scalp Serum helps balance the scalp microbiome, soothing dryness, itching and reducing dandruff flakes. The formula uses peppermint oil for immediate relief, while amino acids, grape, ginger and frankincense restore microbiota balance and provide long-term protection against irritation. Our Solution: Sequential, with its database of over 20,000 microbiome samples and 4,000 ingredients, offers comprehensive services to evaluate product impacts on the microbiome. Our customizable microbiome studies, combined with real-world testing environments, provide critical insights into product efficacy. By partnering with Sequential, you gain access to data-driven solutions that help optimise your formulations and ensure they support scalp health in line with emerging research. References: Choi, J.-Y., Kim, H., Min, K.-H., Song, W.-H., Yu, D.-S., Lee, M. & Lee, Y.-B. (2024) Bacteria, Fungi, and Scalp Psoriasis: Understanding the Role of the Microbiome in Disease Severity. Journal of Clinical Medicine. 13 (16), 4846. doi:10.3390/jcm13164846. Ghafoor, R., Patil, A., Yamauchi, P., Weinberg, J., Kircik, L., Grabbe, S. & Goldust, M. (2022) Treatment of Scalp Psoriasis. Journal of drugs in dermatology: JDD. 21 (8), 833–837. doi:10.36849/JDD.6498.

Fasting, a practice rooted in history and religious traditions, has recently surged in popularity as a health trend. Its benefits - such as weight management, improved metabolic function and delayed ageing - are well-documented. However, new research suggests that fasting may also impact the oral microbiome, influencing oral health in unexpected ways. What We Know: Fasting involves abstaining from food, consuming only water or other approved liquids (e.g., herbal teas or black coffee) for an extended period of time. Different fasting types, such as intermittent fasting (less than 2 days) and long-term fasting (4 days to several weeks), have been studied clinically (Loumé et al., 2024). A lesser-known side effect of fasting is bad breath, or halitosis. This is often anecdotally linked to the "keto flu" during the body’s transition from burning carbohydrates to fat, but while ketone bodies may contribute to foul breath, this phenomenon differs from the pathological halitosis seen in some fasters (Loumé et al., 2024). Studies show that 80-90% of fasters with halitosis have oral microbiome dysbiosis. Oral microbes degrade residual proteins in saliva, food debris and shed epithelial cells, producing volatile sulphur compounds (VSCs) which are linked to halitosis, dysbiosis and periodontal disease (Loumé et al., 2024). Industry Impact and Potential: Recent research on long-term fasting’s effects on halitosis and the oral microbiome uncovered several key findings. Initially, fasting reduced microbial alpha diversity (a measure of species variety), but diversity rebounded and even exceeded baseline levels one and three months after fasting (Loumé et al., 2024). Fasting led to a decrease in genera such as Neisseria, Gemella  and Porphyromonas , while promoting an increase in others, including  Megasphaera, Dialister, Prevotella, Veillonella, Bifidobacteria, Leptotrichia, Selenomonas, Alloprevotella  and Atopobium . Firmicutes (Bacillota) became dominant during follow-up periods, while Proteobacteria  and Bacteroidetes  were suppressed (Loumé et al., 2024). The reduction in potentially harmful species like Porphyromonas  suggests a shift towards a less inflammatory microbial environment. Additionally, the correlation between microbial shifts and increased levels of dimethylsulfide - a compound linked to halitosis - indicates that fasting-induced changes in the microbiota may contribute to breath odour (Loumé et al., 2024). Our Solution: At Sequential, we are a trusted leader in microbiome product testing and formulation. Our customisable solutions empower businesses to innovate with confidence, ensuring the development of effective oral hygiene products that preserve the integrity of the oral microbiome. With our expertise, we help companies explore the potential of microbiome studies and product development not only for oral health but also for skin, scalp and vulvar microbiomes. References: Loumé, A., Grundler, F., Wilhelmi de Toledo, F., Giannopoulou, C. & Mesnage, R. (2024) Impact of Long-term Fasting on Breath Volatile Sulphur Compounds, Inflammatory Markers and Saliva Microbiota Composition. Oral Health & Preventive Dentistry. 22, 525–540. doi:10.3290/j.ohpd.b5795653.