Alopecia categories
Alopecia can either be non-scarring or scarring. Non-scarring alopecia is more common and means that the hair follicles are not destroyed and the skin does not scar. As a result, non-scarring alopecia may be reversible.
Alopecia areata is an autoimmune disease where there are well-defined patches of hair loss. Surrounding hairs are narrower near the base and form characteristic 'exclamation mark' hairs. This usually reverses spontaneously after a few months
Telogen effluvium causes diffuse hair loss after severe physiological stress eg childbirth, illness, surgery.
Androgenic alopecia causes male- or female-pattern balding. In males it presents with a receding hairline and loss of hair on the vertex of the scalp. In females it presents with thinning of the hair.
Nutritional deficiencies and thyroid dysfunction may also cause non-scarring alopecia.
In scarring alopecia, hair follicles are destroyed and the skin becomes scarred. Scarring alopecia is irreversible.
Folliculitis decalvans causes a scarring alopecia with perifollicular pustules (pustules around the base of follicles) and multiple hairs originating from a single follicle. It is thought to be due to infection with Staphylococcus aureus and so treatment is with oral antibiotics.
Lichen planopilaris is a form of lichen planus that causes patches of hair loss - cutaneous lichen planus is also usually seen.
Discoid lupus and tinea capitis may also cause scarring alopecia.