Causes of Male Hair Loss
Alopecia is the medical term for hair loss and the major cause of alopecia is genetic in origin. Hair loss is the result of the interaction of certain hormones circulating throughout your blood cells with the hair follicles themselves. Each individual's genetics determines how this interaction takes place and, subsequently, how much hair loss an individual experiences. Testosterone, which is a hormone present in both men and women, is converted to DHT by a chemical reaction in the blood stream. When DHT binds to receptor sites on the hair follicle, that hair follicle becomes progressively thinner and smaller until it eventually dies.
DHT attacks the hair follicles by binding to receptor sites on the surface of the follicles' cells. This interaction causes healthy, thick hair to thin, becoming smaller and smaller in diameter, until the hair dies. The attack of the hair follicle by DHT causes hair loss in both men and women; however, not all hairs are sensitive to DHT. Hair follicles in the back of the head tend to be resistant to DHT, and therefore these hairs remain permanently on your head. Hairs that remain permanently on your head can be transferred to areas of hair loss by the process of hair transplantation.
Hair growth is cyclical. Each hair goes through three cycles many times during a person's lifetime. Anagen is the active growing phase of hair growth, and it lasts three to ten years. At any one time, approximately 90% of your hair is in the anagen phase. The second phase is the catagen phase, during which time the hair regresses. This phase lasts between two-to-three weeks, and is followed by the telogen or "resting" phase. In the telogen phase, the hair shaft, the non-living part of the hair that we see on the head as our “hair,” is shed and the living inner part of the hair follicle rests or hibernates for 3-4 months. It then begins to grow again and a new anagen cycle begins.
At any one time, approximately 10% of the hairs on your head are in the resting phase, but many different factors, such as stress, surgery, medication, or medical illnesses, can cause a larger percentage of hair to enter the telogen phase. This is very important, as the thinning that accompanies this "telogen effluvium" should correct itself.