Hair and scalp disorders in ethnic populations.

Human hair has been classified into 3 major groups, as determined by ethnic origin. In these populations, significant structural and biochemical variations of the hair follicle and shaft are seen, as well as unique hair grooming practices. These structural variations of the hair are closely linked to the common disorders of the hair and scalp, such as acquired trichorrhexis nodosa, seborrheic dermatitis, traction alopecia, central centrifugal cicatricial alopecia, dissecting cellulitis, frontal fibrosing alopecia, and pseudofolliculitis barbae.