Androgen-related changes in hair growth represent something of a mystery. Through the action of dihydrotestosterone (DHT), hair growth is increased in specific areas of the body. Elevated levels of DHT produce a general increase over the larger part of the body, often accompanied by hair loss in specific areas of the scalp. Because of this 'opposite' effect, a genetic difference in the hair follicles is proposed. This view is supported through the success of the 'plug graft' transplantation technique. However, this is unsatisfactory, because transplantation procedures that should work well according to this theory, ultimately fail. There is an alternative 'mechanism', that demonstrates its origins in the prime function of hair as an insulator. This simple mechanism makes sense of all the recognized effects of DHT in the dermal system, and throughout the body. In DHT-related hair growth it can be directly observed. The implication is that DHT achieves its effects through a primary physiological action that can be easily tested given the necessary expertise. Given existing knowledge, such a proven action of DHT would have serious implications for further understanding of female susceptibility to autoimmune disease.