How Hormones Can Cause Hair Loss

Hair fall normally occurs gradually with age in both men and women but is typically more pronounced in men. People have between 100,000 and 150,000 hairs on their head. The number of strands normally lost in a day varies, but on average is 100. Most people who develop alopecia areata are apparently healthy and have no skin problems. When it does occur, it tends to start during the late teenage years, early childhood, or early adulthood. However, it can strike at any age.

This could happen rapidly, or from progression of alopecia areata. Experts are not sure what causes it but know that it is an autoimmune disorder. Although many believe mental stress is a contributory factor, a sizeable number of people with alopecia lead relatively stress-free lives.

Hormonal influences

Systemic hormonal effects

Key role of androgens in the pathogenesis of male AGA was revealed by the observations of the American anatomist James Hamilton. He noted that men castrated before puberty did not develop balding unless treated with testosterone. A number of studies have tried to determine whether balding males have increased circulating androgens, but no differences between patients and controls have been consistently found.

All these studies suffer from a lack of reproducibility, and although differences in mean levels have been variously detected, the substantial overlap in the absolute levels of all androgens between cases and controls demonstrates that normal male levels of androgen are sufficient to make manifest the degree of baldness determined genetically for the individual.

  Women, androgens in the normal female range are sufficient to induce early baldness in women with a strong genetic predisposition. In women without a strong predisposition, balding will not occur until later in life unless endogenous androgen production is increased or drugs with androgen-like activity are taken. Some women with even grossly abnormal levels of androgen do not develop clinically significant baldness, although such patients are generally hirsute.

Local hormonal effects

 Androgens do not affect all hairs equally. Body hair grows, scalp hair is lost whereas the eyebrows remain essentially unchanged at puberty. On the scalp there is a hierarchy of sensitivity, with the most anterior of the hairs at the temples being lost first, and subsequent hairs miniaturizing in a highly ordered fashion to produce patterned baldness. Similarly, on the male beard, hairs first appear on the upper lip at the lateral corners and then over the rest of the face in a highly ordered fashion.

In men, where circulating androgens are surplus to the requirements of hair follicles for maximal stimulation, local factors determine individual susceptibility and severity of baldness. This intrinsic regulation is best demonstrated in hair transplantation experiments; occipital hairs maintain their resistance to AGA when transplanted to vertex, and scalp hairs from the vertex transplanted to forearm miniaturize at same pace as hairs neighboring the donor site.

In females, where circulating androgens are not sufficient to maximally stimulate hair follicles, local factors still determine susceptibility, but severity is influenced by both local factors and levels of systemic hormone.