Many factors are involved in hair loss. The exact cause is not known but scientists think that stress and severer illness, can cause hair to fall out (Chemistry in Britain). Iron deficiency or pregnancy can cause hair loss in women. Some cases are potentially reversible. For example, hair may re-grow once the illness has been cured.
Scientists also know that the largest cause of hair loss in men is genetic in origin. Alopecia androgenetica, which creates male pattern baldness in men and general thinning of the hair in women, is an ageing phenomenon. They do know that the mechanisms involved in hair loss are complex and mediated to some extent by the male hormone (androgen).
There are also suggestions that genetic hair loss is just an ageing process where the chronological age of an affected individual becomes desynchronized with that of the hair follicles.
The male hormone, testosterone, is pivotal in the physiology of balding. It includes any hairs that are predestined to stop growing. Treating suffers with testosterone can stimulate dormant hair follicles into growth, but giving testosterone to men cause unwanted side-effects.
In genetic hair loss, changes occur in all three fundamental hair variables; hair density (number of hairs per square centimetre0; the proportion of hair follicles in the active growth phase and the hair diameter per unit area. Initially, there is a reduction in the period of active growth, which results in an increase in the number of hairs being shed from scalp. This is followed by a reduction in hair diameter as the hair follicle gradually becomes smaller. Finally, the number of productive hair follicles decreases, reducing the meaningful hair density.
The principle mechanism of genetic hair loss appears to be “localized tissue sensitivity to normal androgen concentrations.” While the metabolic processes are far from clear, an important candidate is the enzyme 5-alpha-reductse inhibitor, which catalyses are reduction of testosterone to dihydrotestosterone (DHT).
