Hair is an important part of who we are. The average person has 5 million hairs (100,000 - 150,000 are on the scalp). Hair is composed of keratin, the same protein that nails and the outer layer of skin is made of. Hairs are produced by a small structure underneath the skin called the hair follicle.

Each hair grows in a series of phases. In the growth phase, the hair is continually growing for up to five years. At the end of the growth cycle, there is a transitional phase where the hair does not grow and begins to change into the third phase. The third phase is the resting phase. During this phase, the follicle is no longer growing, and at the end the old hair is pushed out, then the cycle starts over and a new growth phase starts. This happens repeatedly throughout our lives, and is why even people unaffected with hair loss lose 50-100 hairs per day.

In people affected with genetic hair loss, there appears to be a higher number of hormone receptors in the areas of the scalp with hair loss. In most people affected by hair loss, male hormone levels are the same as in normal people, but because there are more receptors in the balding areas of the scalp they are affected as if their hormone levels were higher than normal. Researchers are still working on how the presence of a certain male hormone, Dihydrotestosterone (DHT), causes damage to follicles in people with genetic hair loss. As the follicles are damaged, the hairs grown are thinner and the growth cycles are shorter with each new growth cycle, until eventually no hair or a small, miniaturized hair is all that can be produced. As more and more hairs become smaller and more miniaturized, the person appears balder.

Genetic hair loss causes about 95% of all hair loss. Another main cause is an autoimmune condition known as Alopecia Areata (patchy hair loss), Alopecia Totalis (loss of all hair on the head), and Alopecia Universalis (loss of all hair on the body). Researchers are also working on a treatment for this condition. Other causes include hair loss due to side effects of medication, stress, or dietary deficiency.

Male pattern hair loss affects nearly 50 million men in the United States, says the American Academy of Dermatology. Approximately 20 percent of the white male population experiences hair loss in their 20s. That percentage rate increases by 10 points for every decade. Other authoritative sources say that 3 in 5 men will be affected by male pattern baldness by the time they reach their 50s.

Scientists did not fully understand the exact cause of genetic hair loss until the early 1990s when scientists discovered that in some hair follicles, an enzyme called 5 alpha reductase combined with testosterone produced dihydrotesterone (DHT). This DHT is harmful to hair follices and "attacks" it, slowly breaking it down, reducing the diameter and length until the follicle falls out, never to be replaced by new hair.

In men with MPHL all the hairs in a DHT affected area may eventually (but not necessarily) become involved in the process and may with time cover the region with fine (vellus) hair. Pigment (color) production is also terminated with miniaturization so the fine hair becomes lighter in color. The lighter color, miniaturized hairs cause the area to first appear thin. - American Hair Loss Council

In men, hair that grows near the temple region, front, vertex (top) and crown (back top of head where it starts to go in a 90 degree angle toward the neck) are most susceptible to DHT. Hair on the back and sides of the head (above the ear but below te top, are the LEAST susceptible to hair loss.

Male pattern hair loss usually begins in the temple region or the crown. From there, the hair on top of the head starts to thin out and the two bald regions can meet. See the The Norwood Hair Loss C