All normal men and women produce "male" hormones. The most common of these are testosterone, androsteinedione, and dihydrotestosterone (DHT). Androgens are produced by the testicles and adrenals in men, and by the ovaries and adrenal glands in women. These hormones are quite important in both sexes, but occur in different concentrations, being much more predominant in males than in females. This, in part, is responsible for the typical differences between the genders.

It is the exposure of the hair follicles to DHT, in a genetically susceptible person, over a period of time, which leads to androgenetic alopecia, or male and female pattern baldness. How does this exposure to DHT occur?

In certain cells of the hair follicle, and in the sebaceous glands, there are high levels of an enzyme called 5-alpha-reductase. What this enzyme does is to convert testosterone, which is delivered to these areas by the blood, into DHT. This is important not only in understanding the mechanisms of balding, but also one medical treatment now available: Propecia (finasteride). What Propecia does is inhibit, or limit the activity of, this 5-alpha-reductase enzyme. Therefore, there is less conversion of testosterone to DHT, and lower levels of DHT are found in the follicle.