There is no set age at which balding occurs. It is a process, and this is a simple, but oft-ignored fact. Like any process, it can be rapid or slow, it can begin toward the end of life or in the late teens, and it can progress in a predictably inexorable fashion, or it can stop and start, seemingly stabilize, and then begin again. Once we understand and accept this as a dynamic process, then we can better plan for the present and for the future in terms of how we treat it. This quest for understanding, which you have begun just by opening this book, will do more than all the despairing thoughts, hand-wringing, and self-pity, toward allowing a clear-eyed, rational, long term approach to the problem of hair loss.

So we now have looked at these three interdependent factors that play into the common types of balding. Again, they are: hormones, genetics, and Father Time. So what exactly does happen to the hair? Let’s take a look.

Assuming we have a genetically predisposed person, then as the follicles are continuously exposed to DHT, an interesting phenomenon occurs. Remember the anagen phase, or active growth phase of the hair? This phase becomes gradually briefer and briefer, and eventually the hair becomes finer and shorter, and less deeply colored. We call this "miniaturization" of hairs. This is also the point at which hair loss tends to first be noticed. It’s not that there are fewer hairs on the head, but that their caliber (cross-sectional area), color and length are so diminished that they no longer provide "coverage" for the scalp beneath. Light penetrates through to the shiny scalp, and this is perceived by the observer as "thinning" or balding.

Also, the ratio between hairs in the anagen phase and those in the telogen, or resting phase, is increased. This simply means that, at any given time, an increased number of hairs are in the telogen phase. These extra numbers of telogen hairs will be found in the susceptible zone for common balding, which is the front, top, and crown of the head. The so-called "permanent" zone, the familiar horseshoe-shaped wreath of hair around the back and sides, is unaffected by these changes. The telogen hairs are easily dislodged during washing, drying, or combing, and this is the second sign of balding: in addition to the apparent thinning seen with miniaturization, we begin to see larger numbers of hairs on the comb, the towel, the pillowcase, or in the bathroom drain. This can be quite traumatic, especially for the younger man or for women. In the next section, we will discuss the natural history of balding, that is, the way it first presents or appears, the different ways it progresses, and how it affects the different regions of the head.

For the sake of completeness, let’s briefly mention some of the other patterns of hair loss, if only to distinguish them from androgenetic alopecia (male and female pattern baldness). There is alopecia areata, where discrete patches of scalp go bald; triangular alopecia, which tend to occur in a triangular pattern in the temporal area; alopecia universalis, in which the entire body may be affected; and various "toxic" alopecias, including those following a severe illness, sometimes with high fever, or following pregnancy. Toxic alopecias may also occur with low thyroid and/or pituitary gland function, or following chemotherapy. The cicatricial (scarring) alopecias occur following tissue destruction and inflammation.

Also seen are the so-called diffuse alopecias (patterned and unpatterned), in which there is widespread thinning that may affect the "permanent" zone as well as the areas vulnerable to balding. In any or all of these less common types of balding above, it may be necessary to have a complete physical and laboratory workup, possibly including scalp biopsy.

So again, the common types of balding are directly related to the presence of male hormones in a genetically predisposed person over time. This can occur in both men and women. The process involves progressive miniaturization of the terminal hairs, and diminished length of the active hair growth cycle. Now, let’s take a look at how this microscopic, cellular process is manifested on the head; we can call this the natural history of balding.