What Microbes Live in the Human Hair Follicle and What Is Their Role?

The human hair follicle hosts a unique microbiome, distinct from that on the skin surface, due to its less acidic, moister environment that is shielded from ultraviolet radiation. This microbiome, consisting of bacteria, fungi, and mites, plays a role in both health and disease. Propionibacterium acnes, the main bacterial inhabitant, is implicated in acne, while changes in the microbiome are also observed in conditions like hidradenitis suppurativa, rosacea, seborrheic dermatitis, and dandruff. Furthermore, the microbiome is altered in hair loss disorders such as androgenetic alopecia and alopecia areata, with Staphylococcus epidermidis potentially protecting against hair loss in alopecia areata. Despite these associations, the exact contribution of the microbiome to disease development is still debated, and our understanding is considered to be in its early stages. The authors suggest that future studies should employ deeper sampling techniques, like biopsies and organ cultures, to better understand the hair follicle microbiome's role in health and disease.