[Nevus comedonicus. A rare skin disease of the hair follicles].

Naevus comedonicus is a rare disorder of the skin which is due to defect development of the hair follicles. The undifferentiated epithelium of the hair follicles produces keratin, which is packed in laminated layers and forms a plug. The keratin plug expands the follicle and gives the clinical appearance of a naevus comedonicus with dark and vaulted crypts of the skin. Comedones appear mainly on the face, neck and trunk. The condition is usually asymptomatic, but may be complicated by infection and scarring. No malignancy has been reported. Local treatment may be application of retinoic acid. This accelerates the exfoliation of the epithelium, and the expulsion of the keratin layers prevents the formation of keratin plugs in the skin. The treatment with retinoic acid will not eliminate the crypts and pits in the skin. Surgical treatment seems to be the best alternative.