Microbiome Disruption

Skin carries a stable community of bacteria, fungi and mites that varies by body site: Cutibacterium acnes dominates oily areas, staphylococci prefer moist ones, Malassezia is present almost everywhere. A healthy community is competitive — resident organisms occupy space and produce compounds that discourage newcomers.

Disruption means that balance shifting rather than the skin becoming sterile. The common causes are alkaline cleansers, which raise surface pH away from the acidic range the resident community prefers; over-cleansing, which strips the lipids and peptides they depend on; and antimicrobials including benzoyl peroxide, which act broadly rather than selectively. Antibiotics do the same from the inside, which is why long antibiotic courses for acne carry consequences beyond resistance.

The associations are real but should be stated carefully. Reduced diversity and altered composition are documented in atopic dermatitis, acne, rosacea and seborrheic dermatitis. Whether that shift causes the condition or follows from it is not settled in most cases, and marketing that promises to fix skin by fixing the microbiome is running well ahead of the science.

What is supportable: a low-pH cleanser, cleansing once or twice a day rather than more, and not applying an antimicrobial where an anti-inflammatory would do. Prebiotic and probiotic claims on cosmetics are mostly unvalidated.