The Arrector Pili Muscle and the Follicular Unit of the Scalp: A Microscopic Anatomy Study

In the 2002 study, researchers analyzed the microscopic anatomy of arrector pili muscles and their relationship with follicular units in the scalp using horizontal skin sections from 20 cadavers. They discovered that hair follicles within follicular units were located above the arrector pili muscle insertions, and these muscles joined to form a single structure per follicular unit at the isthmus level. Masson's trichrome stain helped to outline the follicular units clearly. The findings led to a proposed anatomic model that could enhance the understanding of hair follicle physiology and its potential functions, including the protection of the stem cell-containing bulge region.