To understand what causes male pattern hair loss, it is important to first appreciate that it is substances in our bodies called hormones that are that are responsible for creating the differences we observe between men and women.

Basically, the main set of hormones that give men their masculine qualities - and therefore effectively sets them apart as 'men' is what are referred to as androgens, with the set of hormones responsible for giving women their feminine qualities being what are referred to as estrogens. Now for these hormones to manifest their effects, they work in conjunction with another set of substances in the body called enzymes. In the case of men, for instance, the androgens with which the men are endowed tend to be converted into testosterone (which is the active form of the androgens), through a process which is mainly accomplished with the aid of the enzymes. One such enzyme that is involved in work on androgens is an enzyme called 5 alpha reductase.

What has been noted about 5 alpha reductase, however, is that if it gets mixed with the androgens that have gotten converted into testosterone (as it is wont to do, given that it remains near the sites where this conversion takes place), then we now end up with a substance called dihydrotestosterone. What has been further noted about this dihydrotestosterone (which has to occur whenever testosterone is acted upon by5 alpha reductase) is that it tends to have an adverse effect on the hair follicles of people in whose bodies it is present. The adverse effect on hair follicles in question here is the disconnection of the said hair follicles from the lines through which they receive blood. Now given that the hair follicles depend on the blood to get their supply of nutrients, it follows that their being cut off from blood supply means that they cannot grow (and they are actually bound to die off), which is what leads to the loss of hair that is characteristic of baldness.

Talking of male pattern hair loss, it is also noteworthy to point out that the condition does also affect women, though of course not to the same degree as men. Having discussed the cause of the condition, one would be tempted to ask how this comes about, because we have said that the condition is caused by enzyme actions on male hormone testosterone. But as it turns out, while androgens like testosterone are the hormones that give men their masculine qualities, with estrogens giving women their feminine qualities, the truth of the matter is that the each gender still has some small levels of the other gender's sex hormones. Men therefore have some levels (albeit much lower, in ordinary cases) of estrogens, with women also having some levels of androgens like testosterone in their blood. So it is this relatively lower level of testosterone in women which is responsible for the relatively less severe cases of baldness in women.