Involvement of Mechanical Stress in Androgenetic Alopecia

CONTEXT: Androgenetic alopecia (AGA) is a frequent disorder characterized by progressive hair miniaturization in a very similar pattern among all affected men. The pathogenesis is related to androgen-inducible overexpression of transforming growth factor β-1 from balding dermal papilla cells, which is involved in epithelial inhibition and perifollicular fibrosis. Recent research shows that hair follicle androgen sensitivity is regulated by Hic-5, an androgen receptor co-activator which may be activated by the mechanical stimulation. Moreover, the dermis of scalp susceptible to be affected by AGA is firmly bounded to the galea aponeurotica, so the physical force exerted by the occipitofrontalis muscle is transmitted to the scalp skin. AIMS: To know whether mechanical stress supported by hair follicles is involved in AGA phenomenon. MATERIALS AND METHODS: It is performed with a finite element analysis of a galea model and a schematic representation of AGA progression according to Hamilton–Norwood scale in order to establish the correlation between elastic deformation in scalp and clinical progression of male pattern baldness. RESULTS: The result was a highly significant correlation (r: −0.885, P < 0.001) that clearly identifies a mechanical factor in AGA development. CONCLUSIONS: All these data suggest that mechanical stress determines AGA patterning and a stretch-induced and androgen-mediated mechanotransduction in dermal papilla cells could be the primary mechanism in AGA pathogenesis.