What causes hair loss?
Hair loss in men is an inherited condition called male pattern baldness or androgenic alopecia and this condition accounts for 99% of hair loss in men. This form of hair loss is due to an inherited increased sensitivity to dihydrotestosterone (DHT), which is an active form of testosterone and is converted from testosterone in the hair follicles by the action of the enzyme 5-alpha reductase. Increased conversion of testosterone to DHT is also responsible for hair loss.
DHT in the hair follicles of the scalp is involved in the regulation of hair growth. Normally old hairs fall out to be 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, which eventually do not emerge from the follicle. The miniaturised hair follicles then enter a permanent state of catagen or rest phase, instead of resting before a new growth phase. They stop growing and although they are still alive, they cannot produce normal hairs and at this stage the process cannot be reversed.
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.
Medications for reducing hair loss
Drugs that inhibit the production of DHT are used in the treatment of male pattern baldness. These include finasteride and dutasteride, which are both inhibitors of the enzyme 5-alpha reductase that converts testosterone to DHT. These drugs reduce the amount of DHT in the hair follicle and slow the progression of balding in men with mild to moderate hair loss, but do not restore hair that has been lost for a long time.