With hereditary hair loss (androgenetic alopecia) the hair follicles which hold the hairs in the scalp are damaged. They respond highly sensitively to the male sex hormone testosterone owing to hereditary hypersensitivity. The hair growth phase is considerably shorter. Hereditary hair loss in men is apparent first at the temples and frequently continues with bald patches on the top of the head. Women who are affected have thinner hair along their parting.
Progression of hereditary hair loss
Androgenetic alopecia is dependent on male androgen hormone levels. The first signs of this genetic predisposition are visible after puberty, between the ages of 20 and 30. First of all the hair recedes along the hairline, then it becomes increasingly thinner on the top of the head. With some men, baldness spreads over the whole head. However, many people keep their hair at the sides and at the neck.
In rare cases, however, women also lose hair for hereditary reasons. Neither women nor men with congenital hair loss usually display higher testosterone levels, however. A crucial factor for hair loss is rather the fact that the hair roots react particularly sensitively to the steroid hormone dihydrotestosterone (DHT).
The interplay of various factors
In the case of androgenetic alopecia, three factors thus play a major role:
Just as resistance of the organism decreases in general as you grow older, the resilience of the hair also reduces over the course of the years. Those with a genetic predisposition also lose more hair as they grow older. Strictly speaking, this isn’t hair loss, but a reduced growth of new hairs. Both in women and men, production of the body’s own growth factors such as IGF-1 (insulin-like growth factor), KGF (keratinocyte growth factor) and VEGF (vascular endothelial growth factor) decreases when you are older. Hairs that have fallen out are therefore not replaced due to a lack of growth stimulation.
As messenger substances in the body, hormones have numerous functions. They influence the duration of the hair cycle and division activity of the hair follicles.
Even as early as the age of 20, production of the growth hormone HGH decreases. Every ten years production reduces by another 14 per cent. As fewer growth hormones are released, the structure and density of new hair also reduces accordingly.
Age-related hair loss usually only occurs in women after the menopause. Production of female sex hormones reduces and the damaging effect of dihydrotestosterone on the hair follicles can become prominent. Women can therefore also be affected by hormonal hair loss, in addition to men. Previously healthy hairs seem thin and lustless.
People who suffer from hereditary hair loss - whether men or women - have inherited hair root sensitivity to the hormone DHT (dihydrotestosterone), which is formed as a result of the body’s own chemical process from the male sex hormone testosterone.
Enzyme 5-alpha reductase
The male sex hormone testosterone is converted into dihydrotestosterone (DHT) by the enzyme 5-alpha reductase. In turn, the hair follicles of people with hereditary hair loss respond extremely sensitively to DHT. DHT damages and weakens the hair roots. There are two types of the enzyme 5-alpha reductase:
5-alpha reductase I (5AR1) only at the front of the scalp
5-alpha reductase II (5AR2) in the entire scalp
If hair loss as a result of DHT is not treated, the hair roots shrink further and further. The hair structure changes as a result, too: instead of the previously strong, full-pigmented hair (terminal hairs), only downy, thin, colourless hairs grow (vellus hair). Under the microscope it is clear how the roots reduce in size until they are a vestige of the outer part of the cell.
In the case of people with hereditary hypersensitivity to DHT, the hair growth phase (anagen phase) shortens and thus also reduces the maximum achievable length of the hair. A bald man may not have fewer hair follicles than a man with a full head of hair, but the hairs are hardly visible due to the shortened growth phase. The scalp on the rear of the head and in the neck area is usually less sensitive to DHT. For this reason, these hairs are suitable, for example, for hair transplants owing to hereditary hair loss.