The Cutaneous Mycobiome in the Follicular Occlusion Tetrad: Evidence, Mechanisms, and Clinical Implications

Abstract

The cutaneous mycobiome is an underexplored component of the skin microbiome with potential relevance to chronic inflammatory follicular disorders. While bacterial dysbiosis has been extensively studied, the contribution of fungal organisms to follicular occlusion diseases remains incompletely defined. This narrative review examines available evidence regarding fungal involvement in the follicular occlusion tetrad, including hidradenitis suppurativa, acne conglobata, dissecting cellulitis of the scalp, and pilonidal sinus. Across these conditions, fungi (most commonly Malassezia and Candida species) are detectable within follicular units but are not consistently enriched in lesional skin. Current data suggest that fungi function primarily as secondary colonizers, inflammatory modifiers, or diagnostic mimickers rather than primary pathogenic drivers. Evidence supporting a direct fungal role is most limited in pilonidal sinus disease and more frequently involves clinical mimickers in dissecting cellulitis and acne conglobata. Notably, immune pathways implicated in follicular occlusion disorders, including Th17-mediated and interleukin-17 signaling, also play central roles in antifungal host defense. Therapeutic modulation of these pathways may therefore influence fungal susceptibility. Overall, existing evidence does not support a primary pathogenic role for fungi but highlights their potential relevance in select clinical contexts.