Management of the human hair follicle microbiome by a synthetic odorant

Background: Human scalp hair follicles (HFs) engage in olfactory receptor (OR)-dependent chemosensation. Activation of olfactory receptor family 2 subfamily AT member 4 (OR2AT4) by the synthetic, sandalwoodlike odorant Sandalore (R) up-regulated HF antimicrobial peptide expression of dermcidin (DCD), which had previously been thought to be produced exclusively by sweat and sebaceous glands. Objectives: To understand if intrafollicular DCD production can be stimulated by a commonly used cosmetic odorant, thus altering human HF microbiome composition in a clinically beneficial manner. Methods: DCD expression was compared between fresh-frozen scalp biopsies and microdissected, fulllength scalp HFs, organ-cultured in the presence/absence of the OR2AT4 agonist, Sandalore (R) and/or antibiotics and/or the competitive OR2AT4 antagonist, Phenirat (R). Amplicon-based sequencing and microbial growth assays were performed to assess how this treatment affected the HF microbiome. Results: Synthetic odorant treatment upregulated epithelial DCD expression and exerted antimicrobial activity in human HFs ex vivo. Combined antibiotic and odorant treatment, during an ex vivo dysbiosis event, prevented HF tissue damage and favoured a more physiological microbiome composition. Sandalore (R) conditioned medium, containing higher DCD content, favoured Staphylococcus epidermidis and Malassezia restricta over S. aureus and M. globosa, while exhibiting antimicrobial activity against Cutibacterium acnes. These effects were reversed by co-administration of Phenirat (R). Conclusions: We provide the first proof-of-principle that a cosmetic odorant impacts the human HF microbiome by up-regulating antimicrobial peptide production in an olfactory receptor-dependent manner. Specifically, a synthetic sandalwood-like odorant stimulates intrafollicular DCD production, likely via OR2AT4, and thereby controls microbial overgrowth. Thus, deserving further exploration as an adjuvant therapeutic principle in the management of folliculitis and dysbiosis-associated hair diseases. (c) 2023 Japanese Society for Investigative Dermatology. Published by Elsevier B.V. All rights reserved.