Hair-Raising Mysteries of the Inner Root Sheath: Unearthing Treasures in Bald Spots

June 2025

Andrew Verbinnen

inner root sheath hair follicles folliculogenesis anagen phase cell differentiation immunomodulation keratinization

TLDR The inner root sheath in hair follicles plays a key role in hair growth and health.

The review re-evaluates the role of the inner root sheath (IRS) in human hair follicles, traditionally seen as a structural component. It suggests that the IRS has broader functions, including involvement in signaling processes that affect folliculogenesis, anagen phase regulation, cell differentiation, immunomodulation, and keratinization. This positions the IRS as a dynamic and significant player in hair follicle biology, with important regulatory functions that have been previously underexplored.

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