Hair Loss for Men

Causes of Hair Loss in Men

Causes of Hair Loss in Men

By far the most common cause of hair loss in men is androgenetic alopecia, also referred to as “male pattern” or “common” baldness. It is caused by the effects of the male hormone dihydrotestosterone (DHT) on genetically susceptible scalp hair follicles. This sensitivity to DHT is present mainly in hair follicles that reside in the front, top, and crown of the scalp (rather than the back and sides) producing a characteristic and easily identifiable pattern described by Norwood (see Norwood Classification).

It is frequently stated that “hair loss comes from the mother’s side of the family.” The truth is that baldness can be inherited from either parent. However, recent research suggests that the reasons for hair loss and balding may be a bit more complex than originally thought. Factors on the x-chromosome have been shown to influence hair loss, making the inheritance from the maternal side of the family slightly more important than the paternal one (Markus Nothen, 2005).

The identification of an androgen receptor gene (AR) on the x-chromosome helps to explain why the hair loss pattern of a man resembles his maternal grandfather more often than his father. However, this is clearly not the whole story since a direct inheritance of baldness from the father is observed as well. An autosomal (non-sex) linked gene would explain this type of transmission – but this gene has not yet been found.

DHT is formed by the action of the enzyme 5-alpha reductase on testosterone, the hormone that causes sex characteristics in men. DHT causes male hair loss by shortening the growth, or anagen, phase of the hair cycle, causing miniaturization (decreased size) of the follicles, and producing progressively shorter, finer hairs. Eventually these hairs totally disappear.

In the patient below, we see a close-up of the side of his scalp where the hair is not affected by DHT. We see mostly groups of full thickness hairs (called terminal hairs) and a few scattered fine, vellus hairs. This is normal.

In the area of thinning most of the hair has been miniaturized, although all of the hair is still present.

In the region that is balding  there is extensive miniaturization and some, but not all of the hair has disappeared.

What this shows is that the initial appearance of balding is due to the progressive decrease in hair shaft size, rather than the actual loss of hair – in early hair loss, all the hair is still present. This is the reason why hair loss medications, such as finasteride (Propecia) work in early hair loss (since they are able to partly reverse the miniaturization process) but don’t work in areas that are totally bald. It is also the reason why men’s hair restoration surgery, if not planned properly, can result in hair loss due to the shedding of surrounding miniaturized hair.