15. What is the difference between alopecia areata and alopecia androgenetica?

Alopecia areata is an auto-immune disease in which the white blood cells attack the hair follicles as though they were foreign bodies. Alopecia areata is a scalp disease which starts in round patches on the head (see alopecia areata). In alopecia androgenetica, the picture is that of ‘male pattern baldness’ which is normally found in older men and to some extent also older women. Today, it is also found increasingly in many younger women. Signs of alopecia androgenetica in a man are receding temples with perhaps a bald patch on the crown; in a woman, it occurs as diffuse thinning of the hair over the entire scalp area so that the scalp shines through (see alopecia androgenetica).