One hair loss cycle lasts about three years and once it’s finished new hair starts to grow. The person that gets affected with hair loss, goes through few stages: affected hair follicles on the scalp gradually become smaller than normal, as the follicle shrinks, each new hair is thinner than the previous one, before falling out, each new hair grows for much less time than the normal three years or so and eventually, all that remains is a much smaller hair follicle and a thin stump of hair that does not grow out to the skin surface.
Hair loss that affects men is caused by male hormones when the hair follicles convert testosterone into another hormone called dihydrotestosterone. After this hair follicles become more sensitive to dihydrotestosterone, causing the hair follicles to shrink. The reason why hair loss is gradual is not clear. Male pattern baldness is genetically determined. This cause of baldness is also known by the name of androgenic alopecia, which is inherited sensitivity to the effects of androgens (male hormones) on scalp hair follicles which causes them to shrink and prevents them from producing hair normally.
Post-pubertal individuals that get affected with this condition experience miniaturizing of the hair follicles, especially on the scalp center and over the temple. There often begin to grow small, fine hairs that are often difficult to see. This process is due to the metabolism of testosterone by an enzyme in the hair follicle. Generally, hair follicles over the ears and around the posterior of the scalp do not possess this enzyme so a fringe of normal hair is maintained.
Patients affected with classic pattern baldness usually lose their hair in a defined pattern, when hair starts to fall above the temples and at the crown of the head. Influence of androgens causes follicles in the temporal, frontal and vertex area of the scalp to show a shortening of the Anagen phase, followed by miniaturization of the hair follicles. It affects the percentage of hairs in Anagen phase and the duration of Anagen diminishes in areas affected by Androgenetic alopecia which results in shorter hairs. It is also known by the term "Hippocratic balding" and it may sometimes progress to complete baldness.
When serum androgen levels rise above the low level, which is usually after puberty, is when men get affected with male-pattern baldness. There are some evidences that when men lose hair in their early twenties, they will lose their hair most extensively if the cause is alopecia. Alopecia is associated with several medical conditions including coronary heart disease and enlargement of the prostate, as well as disorders of insulin resistance, like diabetes and obesity and high blood pressure. In most cases, men have some type of baldness by the time they are in their 60s, but the age when the hair loss starts is variable. Some women also develop a similar type of hair loss, mainly at the crown. Baldness in women is much more common after the menopause.
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