Skincare University

Skin microbiome and fermented ingredients — how they interact

LEVEL 4
The World of Fermented Ingredients

※ The information in this section is based on Japanese cosmetics regulations (Pharmaceutical and Medical Device Act / 薬機法). Ingredient classifications, permitted concentrations, and labeling requirements may differ in your country or region.
LEVEL 4 The World of Fermented Ingredients

Our skin hosts approximately 1 million microorganisms per cm². Understanding the relationship between this "skin microbiome" and fermented ingredients is central to next-generation skincare.

Key players in the skin microbiome

Staphylococcus epidermidis is the most dominant commensal bacterium, producing antimicrobial peptides (AMPs) that prevent pathogen colonization. It also metabolizes glycerin to generate moisturizing factors.

Cutibacterium acnes breaks down sebum to produce propionic acid, maintaining the skin's mildly acidic pH. While overgrowth causes acne, its moderate presence contributes to barrier function.

Malassezia is a fungal genus that feeds on sebum to produce fatty acids. Overgrowth can cause seborrheic dermatitis and dandruff.

Sphingomyelinase and ceramide conversion

The sphingomyelinase produced by S. epidermidis converts sphingomyelin in the stratum corneum into ceramides. Ceramides form the lamellar structure that is fundamental to barrier function. In other words, healthy commensal bacteria maintain the skin's barrier.

Dysbiosis and skin problems

Dysbiosis (disruption of the microbial balance) is caused by excessive cleansing, antibiotic overuse, and stress. S. aureus overgrowth is linked to atopic dermatitis, C. acnes overgrowth to acne, and Malassezia overgrowth to seborrheic dermatitis.

Skin Microbiome Balance Balanced Eubiosis S. epidermidis C. acnes Others pH 4.5-5.5 maintained AMP production Ceramide generation Immune regulation Healthy Skin Imbalanced Dysbiosis S. aureus overgrowth Beneficial depleted pH elevated Barrier breakdown Inflammation Immune overreaction Skin Problems vs

How fermented ingredients affect the microbiome

Postbiotics (fermented ingredients) support the microbiome through the following mechanisms:

1. pH maintenance: Lactic acid and organic acids keep the skin's pH mildly acidic (4.5-5.5), maintaining a beneficial bacteria-dominant environment.
2. Antimicrobial peptide supply: Bacteriocins produced during fermentation selectively suppress pathogen growth.
3. Treg differentiation promotion: Short-chain fatty acids (butyrate, propionate) promote regulatory T cell (Treg) differentiation, suppressing excessive immune responses.

Immunomodulatory action of short-chain fatty acids

Short-chain fatty acids (SCFAs) inhibit histone deacetylase (HDAC), promoting anti-inflammatory cytokine (IL-10) production while suppressing pro-inflammatory cytokines (IL-6, TNF-alpha). This immunomodulatory action is the scientific basis for why fermented ingredients show efficacy for sensitive skin and atopic dermatitis.

KAIAN develops skincare products formulated with a 3-strain fermentation complex.
Feel free to reach out with questions.

Contact Us
← Back to Skincare University