An irreversible alopecia of the scalp occurs in Negro women who straighten their hair with hot combs. The disease is common and distinctive, clinically and histopathologically. The hair loss is incomplete and strictly limited to the crown. The follicles between the surviving hairs are completely obliterated.
The hot petrolatum used with the iron causes a chronic inflammation around the upper segment of the hair follicle leading to degeneration of the external root sheath. Ultimately, the entire follicle is destroyed and replaced with a band of dense collagen, a follicular scar.
LoPresti P, Papa CM, Kligman AM. Hot Comb Alopecia. Arch Dermatol. 1968;98(3):234-238. doi:10.1001/archderm.1968.01610150020003