1. pH changes
Healthy skin is slightly acidic (around pH 4.5–5.5). Many cleansers, soaps, and exfoliants are more alkaline.
- Acidic pH supports beneficial microbes such as Staphylococcus epidermidis.
- Alkaline products disrupt this balance, making it easier for opportunistic pathogens like S. aureus to colonise.
Even small pH shifts can alter which microbes thrive on the skin.
2. Removal of natural oils
Sebum is a key nutrient source for many commensal microbes.
- Harsh cleansers strip lipids, reducing food sources for beneficial bacteria.
- This can weaken colonisation resistance — the skin’s natural ability to prevent pathogen overgrowth.
The Nature article emphasises that P. acnes (now Cutibacterium acnes) thrives in oily environments, while other microbes dominate dry areas. Removing oils changes this ecological balance.
3. Antimicrobial ingredients
Some skincare ingredients kill microbes indiscriminately.
- Alcohols, benzoyl peroxide, triclosan, strong preservatives
- Reduce microbial diversity
- Lower diversity = higher risk of irritation, eczema, acne flares
Studies highlight that commensal microbes produce natural antimicrobials (e.g., S. epidermidis producing proteases that inhibit S. aureus). When these commensals are reduced, pathogens gain space to grow.
4. Occlusive or heavy formulations
Thick, occlusive products can create low‑oxygen environments.
- This may encourage anaerobic bacteria such as C. acnes.
- It can also disrupt the balance between aerobic and anaerobic species.
Microbial communities adapt quickly to changes in moisture and oxygen availability.
5. Preservatives and surfactants
Preservatives are essential for product safety, but some are more microbiome‑disruptive than others.
- Strong surfactants (e.g., SLS) can damage the skin barrier, indirectly altering microbial composition.
- Certain preservatives can reduce beneficial species more than harmful ones.
Barrier disruption is a major driver of dysbiosis, as the Nature article notes that healthy skin relies on intact physical and chemical defences.
6. Supportive, microbiome‑friendly formulations
Not all products are harmful — some actively support microbial balance.
- Gentle, pH‑balanced cleansers maintain the acidic mantle.
- Natural oils and humectants help preserve the environment commensals need.
- Prebiotics (e.g., inulin, xylitol) feed beneficial microbes.
- Postbiotics (microbial metabolites) can enhance barrier function and immunity.
These approaches align with the paper’s emphasis on the protective roles of commensal microbes, such as S. lugdunensis producing lugdunin to inhibit pathogens.
Why these matters
The skin microbiome is a living defence system. When skincare products disrupt it:
- Pathogens can colonise more easily
- Inflammation increases
- Barrier function weakens
- Conditions like acne, eczema, and dermatitis become more likely
When products support it, the skin becomes more resilient, balanced, and less prone to irritation.
Hou, K. et al. (2022) ‘Microbiota in health and diseases’, Signal Transduction and Targeted Therapy, 7, p.135. Available at: https://www.nature.com/articles/s41392-022-00974-4.
NHS England (2024) Antimicrobial resistance (AMR). Available at: https://www.england.nhs.uk/ourwork/prevention/antimicrobial-resistance-amr/.
Grice, E.A. & Segre, J.A. (2011) ‘The skin microbiome’, Nature Reviews Microbiology, 9(4), pp.244–253. Available at: https://www.nature.com/articles/nrmicro2537.
Byrd, A.L., Belkaid, Y. & Segre, J.A. (2018) ‘The human skin microbiome’, Nature Reviews Microbiology, 16(3), pp.143–155. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC3535073/.
WebMD (2023) What Is the Skin Microbiome? Available at: https://www.webmd.com/skin-problems-and-treatments/skin-microbiome.