The Hair Loss Process (The DHT Theory)
(The most widely accepted theory)

The speed at which hair loss occurs in androgenic alopecia is dependant on by three things:
1) Progression in age.
2) Heredity tendency to have hair loss
3) The prevalence of dihydrotestosterone (DHT) within the hair follicle

DHT is a highly active form of testosterone, which influences many aspects of manly behavior, from sex drive to aggression. DHT is a naturally occurring hormone which assists with sexual development in males during fetal development and puberty. DHT which is produced in the prostate, various adrenal glands, and the scalp is produced from testosterone by two 5-alpha reductase isoenzymes, called Type I and Type II. Type I 5AR is much more prominent in the scalp than Type II. However, immunostaining techniques reveal that Type I is abundant in sebaceous glands, while significant Type II is present in the dermal papilla itself. DHT is the androgen thought to be most responsible for male pattern baldness. DHT has a very high affinity for the androgen receptor and is estimated to be five to ten times more potent than testosterone. Other androgens that may be significant in pattern loss include androstenedione, androstanedione and DHEA (especially in women). All of these fall into hormonal pathways that can potentially result in elevation of DHT downstream via various enzymes.

It is possible that certain DHT metabolites may play a role in pattern loss as well. During hair loss, DHT begins to treat your follicles as foreign objects in your body. Similar to an auto-immune response, it slowly begins to reject the follicles. During this time there typically is increased Sebum production. During hair loss, DHT begins to treat your follicles as foreign objects in your body. Follicles at the front, top, and upper back of the head in most men are genetically programmed to become susceptible to DHT at some point in the man's life. Those hairs which cover the sides and bottom back of the head typically are not, which is why most men do not lose hair in these areas. This is lengthy progression, and the cycles for hair growth are typically about 3-9 months. Without a DHT inhibitor either systemically (in the bloodstream) or locally in the scalp, each time your hair cycles, the follicle will become thinner, shorter, and ultimately it will not grow back in. Over time, the action of DHT will cause each hair follicle to decay and shortens the anagen phase. Some follicles will gradually die, but most will simply shrink to the size they were when you were born which produce weaker hairs. With a progressively shorter anagen growing cycles, more hair is lost, and the remaining hair becomes finer and thinner until they are too fine to survive.

The sebaceous gland (gland producing sebum - natural oil) attached to the hair follicle remains the same size. As the hair shafts become smaller, the gland continues to pump out about the same amount of oil (sebum). So as your hair thins, you will notice that your hair becomes flatter and oilier. Some studies have shown that while men with hair loss don't have higher than average circulating testosterone levels, they do possess higher than average amounts.

Other physiological factors might cause hair loss. Recently, a group of Japanese researcher reported a correlation between excessive sebum in the scalp and hair loss. Excessive sebum often accompanying thinning hair is attributed to an enlargement of the sebaceous gland. They believed excessive sebum causes an high level of 5-alpha reductase and pore clogging, thus malnutrition of the hair root. Although this condition could be hereditary, they believe diet is a more prominent cause. The researchers note that Japanese hair was thick and healthy, with a small gland and little scalp oil, until the occidental habit of consuming animal fat crept into their diet after World War II.

This change has led to a significant height increase in the Japanese population, but it has also resulted in more Japanese men losing hair. To some extent, their observation makes sense since problems with greasy hair have often been noted as much as six months to a year prior to when thinning hair becomes noticeable, but this might be just one of the symptoms, not underlying cause, more research is needed. Most doctors agree that if you have a oily scalp with thinning hair, frequent shampooing is advised. shampooing can reduce surface sebum, which contains high levels of testosterone and DHT that may reenter the skin and affect the hair follicle.