Alopecia areata incognita: a hypothesis.

To explain why in alopecia areata the hair falls out in a particular area the hypothesis is proposed that the area occurs as a stochastic event only in those subjects who, in a restricted zone of their scalp, happen to have a group of hairs that are simultaneously in the early anagen VI subphase of the hair cycle. Once this point has been accepted, a number of conclusions may be drawn. Especially important is the inference that only people with low percentages of telogen hairs are likely to exhibit areas, whereas those with androgenetic alopecia, when affected by alopecia areata, preferentially show a diffuse and delayed hair loss that has the features of Kligman's telogen effluvium (alopecia areata incognita). Epidemiological evidence is provided.