Hair follicles are formed while we are still a fetus, and after we are born no new follicles are produced. Hair growth is often regulated by hormones within the body. At puberty, certain male hormones trigger the growth of pubic, underarm, and beard hairs. They can also trigger the start of genetic male pattern hair loss.
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.
