Miniaturized Hairs Maintain Contact With the Arrector Pili Muscle in Alopecia Areata but Not in Androgenetic Alopecia: A Model for Reversible Miniaturization and Potential for Hair Regrowth

The study found that miniaturized hairs in alopecia areata maintain contact with the arrector pili muscle (APM) while miniaturized hairs in androgenetic alopecia lose contact with the APM. The researchers suggest that the persisting contact between the APM and outer root sheath (ORS) predicts reversibility of miniaturization, which could explain complete hair regrowth in AA while hair loss is largely irreversible in MPHL and FPHL. The regression of the APM may be the result of a disease process that disrupts a stem cell population which maintains the APM as well as the follicle.