DHT Inhibitors

Effect of DHT of hair growth

Dihydrotestosterone (DHT) is an active form of testosterone that binds strongly to the androgen receptor. DHT is found in several tissues throughout the body including the hair follicles of the scalp, and is involved in the regulation of hair growth.

Normally as old hairs fall out they are replaced by new hairs. However, increased action of DHT results in shortening of the anagen or growth phase of the hair cycle, causing the hair follicles to shrink and produce progressively smaller finer hairs that are pale and translucent and that eventually do not emerge from the follicle. These hairs are known as vellus hair and the process is known as miniaturisation of hair follicles. Vellus hair is fine hair that grows on most parts of the body except the lips, palms of the hands and soles of the feet. The miniaturised hair follicles enter a permanent state of catagen or rest phase, instead of resting before a new growth phase. They eventually stop growing and, although they are still alive, they cannot produce normal hairs.

DHT also stimulates the production of another chemical called transforming growth factor beta (TBG beta), which blocks growth of the skin cells that support hair follicles and eventually cause cell death.

5α-reductase inhibitors

Once a hair follicle is in permanent catagen and has stopped producing new hairs, the process of hair loss cannot be reversed. However, it is possible to prevent hair follicles from shrinking that are not yet affected, by inhibiting the action of the enzyme type II 5α-reductase that converts testosterone to DHT.

Finasteride and dutasteride are both 5α-reductase inhibitors that are used to prevent the progression of hair loss leading to male pattern baldness and thereby, reverse the balding process. These medications are more successful when used at an early stage of the balding process but cannot restore hair growth to areas where hair has been lost for some time.

Some natural plant products called phytosterols also have activity as inhibitors of 5α-reductase, such as saw palmetto, which are used as nutritional supplements to help prevent hair loss.