In the vast majority of men who experience balding, the cause is a condition referred to in the medical literature as "Androgenetic Alopecia". This is a fancy term for the kind of balding that we commonly call male pattern baldness. "Pattern" baldness is simply what the name implies. It occurs in a pattern and is usually not related to any disease process.

Andro refers to Androgens or male hormones. Male hormones are normally present to a greater degree in men and to a much lesser degree in women. The term genetic refers to the genetic or inherited nature of balding. This is how it works. Every hair follicle has a genetic program inherited from both parents at conception (not the mother only) that controls this type of hair loss. At some point in time, because of this genetic program, certain follicles within the balding pattern become sensitive or vulnerable to the follicle killing effects of male hormone or "Androgen." Other follicles outside the pattern with a different genetic program remain insensitive or invulnerable to these effects.

So it's not the location of the follicle, but the follicle itself, and more specifically the genetic program of each follicle. These Androgen sensitive follicles then begin to change; they become progressively smaller, called miniaturization (see illustration below) and grow progressively shorter hair shafts because of a shortened growth phase (see illustration below).

Please note, hair follicles exist in three phases of growth:

1. A growth phase called the Anagen phase, typically lasting three or four years, followed by
2. A short shriveling up phase called the Catagen phase, followed by
3. A dormant or resting phase called the Telogen phase, usually lasting three or four months.

Most of your follicles, approximately 90% to 95% (most people start out with about 100,000 hair follicles), are in the growth phase, growing approximately one half inch per month.

An average anagen or growth phase will last three years or more. This will allow the hair shaft to grow about 18 to 24 inches before it sheds, or falls out. This happens when the growing follicle changes phases (see illustration below). This change in phase is why we normally shed 50 to 100 hairs per day.

Some individuals actually have follicles with an unusually long growth or anagen phase, permitting the hair shafts to grow several feet in length before falling out. Remember that cheerleader in high school who had hair down past her waist? She obviously had follicles with a very long anagen phase. If however, your growth phase is unusually short, the hair shaft won't achieve much length. As mentioned, that's one of the things that happens when the "Androgen sensitive" follicles within the pattern are continually exposed to normally present male hormone or Androgen.

Let's recap and put it all together. Each hair follicle has a genetic code determined at conception. This genetic code controls "if" and "when" each follicle will become vulnerable to the hair killing effects of normally present male hormone or Androgen. When this happens, Androgen begins to slowly kill the now vulnerable follicles by:

As a result, the hair within the pattern becomes progressively finer, shorter, and falls out more frequently.