Your skin is not alone. Its surface is home to a community of between one million and ten million microorganisms per square centimeter—bacteria, fungi, viruses, and mites—that are not invasive pathogens but permanent residents actively contributing to skin health. The skin microbiome is, in many ways, as important to skin function as the tissue that supports it.
What is the skin microbiome and what does it do?
The skin microbiome is the set of microorganisms that colonize the skin commensally or mutualistically. The most studied bacterial species in healthy skin is Staphylococcus epidermidis, which competes with pathogens such as Staphylococcus aureus, produces antimicrobial peptides, regulates the innate cutaneous immune response, and contributes to maintaining the skin's acidic pH (between 4.5 and 5.5), which inhibits the growth of many pathogens.
Studies such as Byrd et al. (2018) in Cell have characterized the diversity of the skin microbiome and its variation according to anatomical area, age, sex, and habits. A balanced microbial composition—with high diversity and a predominance of commensal species—is associated with an intact barrier function, reduced reactivity, and decreased skin inflammation.
How it becomes unbalanced: common aggressors
Skin dysbiosis—an imbalance of the skin microbiome—can be caused by multiple factors: excessive use of soaps and cleansers with alkaline pH that alter the skin's acidic environment, frequent application of topical antibiotics that reduce microbial diversity, chronic stress (which affects both the gut and skin microbiome through the neuroendocrine axis), a pro-inflammatory diet, and the use of very hard water that alters skin pH.
Skin microbiome and gut microbiome: the gut-skin axis connection
The gut-skin axis is one of the most active research fields in dermatology and microbiology. Accumulated evidence shows that gut dysbiosis—an imbalance of the digestive tract microbiome—is associated with skin conditions such as acne, atopic dermatitis, rosacea, and psoriasis. Proposed mechanisms include the translocation of bacterial lipopolysaccharides into the bloodstream, the modulation of the systemic immune response, and the production of metabolites that affect skin barrier function.
This implies that skin care has a dimension that goes beyond topical and nutricosmetic approaches: gut health—through diet, prebiotics, and the reduction of microbiome disruptors—has a direct impact on the skin microbiome and, through it, on skin inflammation and balance.
What role do nutrients play in regulating the skin microbiome?
Zinc has direct antimicrobial activity against S. aureus and modulates the skin immune response. Vitamin A regulates keratinocyte differentiation and the expression of antimicrobial peptides. Selenium activates selenoproteins that control oxidative stress in the barrier environment. Systemic antioxidants reduce the inflammatory environment that promotes the overgrowth of opportunistic pathogens.
