Mechanism of male pattern baldness

While the precise mechanism which underlies androgenic alopecia is unknown, a high level of dihydrotestosterone (DHT) is crucial in initiating the process. DHT is, ironically, a hair growth stimulator. Testosterone is synthesized from pregnalone which is formed from cholesterol. DHT is formed from Testosterone with the conversion from testosterone to DHT being mediated by 5-alpha reductase. There are two subtypes of 5-alpha reductase and drugs which block one type may not block the other.

While androgens (the general class of male hormones which includes testostrone and DHT) levels may be similar in men who have male pattern baldness and those who have hair, people with more 5-alpha reductase or a greater density of DHT receptors may be more vulnerable to the effects of DHT. Surprisingly, men with male pattern baldness have, on average, significantly lower levels of total testosterone, though they did not have significantly lower levels of unbound androgens in their blood.

Spiking androgen levels, caused by intense weight training, sudden weight loss, taking anabolic steroids or other synthetic androgens and other causes can promote the balding process. The vast majority of anabolic steroids contribute to hair loss, since most anabolic compounds break down to form DHT at some point.

How DHT causes hair loss is hotly debated.

American research tends to focus on DHT, DHT receptor density in the scalp and 5-alpha reductase levels in the scalp as causes of baldness.

Japanese research may cover these topics but also is more likely to cover the increase in sebum (scalp oil) production caused by DHT in the scalp, and the increase of Pityrosporon ovale, a pathogenic yeast which has been linked to dandruff and eczema, and which feeds off of sebum. Issues related to diet are also more likely to be covered. Possibly this is because male pattern baldness has increased very sharply in Japan since the end of World War II along with an increase in fatty foods and average height, focusing public attention on various lifestyle differences.

Most pharmaceutical treatments which stop or slow the balding process work by limiting the creation of DHT. In ideal situations this may cause a person's hairline to revert to what it was a year ago (since follicles which were resting but healthy will be active again), though it is difficult to reverse more than a year of hair loss without surgery.

Since sex hormone binding globulin is reduced by high insulin levels, reducing insulin levels should also increase levels of sex hormone binding globulin. Higher SHBG binds to testosterone, preventing its conversion to DHT. Less free testosterone means that less testosterone will be converted into DHT, even if total testosterone levels are very high.

Statistically, men who are bald are more likely to be insulin resistant and more likely to suffer cardiovascular disease. There seems to be a correlation between male pattern baldness and metabolic syndrome, though androgens are not shown to cause heart disease or metabolic syndrome\diabetes directly. High insulin levels seem the likely link between the two conditions.

Chronic infection with a diseases such as Chlamydia, exposure to pathogenic mold, and high levels of stress can exacerbate androgenic alopecia. How this happens isn't always clear. Some types of stress can cause decreases in plasma levels of sex hormone binding globulin, among other responses.

Table of Contents:
Male pattern baldness
Female pattern baldness
Evolutionary theories of male pattern baldness