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Androgenic alopecia

This page aims to give you a general overview of hair disorders.

Androgenic alopecia is the most common form of hair loss. It is due to the hair follicles being hypersensitive to male hormones and, although it is much more common in men, women can also be affected.

Progressive hair loss

Androgenic alopecia starts with the hair becoming finer and then less dense, and finally, in certain cases, certain parts of the scalp can become completely bald. The hair loss is always gradual, but it can be steady or progress sporadically, particularly during periods of stress or intense fatigue. The rate of hair loss varies greatly from one person to the next.
Androgenic alopecia most often starts between the ages of 40 and 50, but can sometimes appear as early as puberty. When it starts early, it generally worsens over time. This condition is most common in men, with 50% of them affected at age 50. However, 15 to 20% of women are also affected at some point in their life.

Accelerated ageing of hair follicles

Androgenic alopecia is due to an increased sensitivity of the hair follicles to androgens. These male hormones, including testosterone, combine with an enzyme present in the scalp’s hair follicles, 5-alpha reductase, to produce another hormone called DHT.
The latter stimulates the hair follicles excessively, thus disrupting their life cycle. First, the duration of the anagen phase (hair growth phase) decreases, resulting in more significant hair loss. In parallel, the new growth cycle starts late, and the hair follicles produce ever finer hair until they become worn out and completely inactive. The hair then disappears, the follicles recede into the dermis and the skin becomes smooth.
It’s the abnormal reaction of the hair follicles that is responsible for androgenic alopecia, not the quantity of male hormones present. This hyperreactivity is often hereditary, but the genetic mechanisms of alopecia are complex and it remains difficult to predict.

Characteristic patterns

In men, the balding caused by androgenic alopecia generally starts at the temporal gulfs or the forehead, and continues on the back of the head (bald spot), then extends to the sides on the top of the scalp. However, each man’s baldness will evolve differently. In all cases, a crown of hair is spared around the lower part of the head, because the hair in this area has no androgen receptors.
In women, the pattern is different. Most often, it starts on the top of the head around the centre part. Then this zone gradually extends until it also reaches the back of the head. A small line across the front generally remains unaffected.
In other, rarer cases, women can notice their hair thinning along the forehead or the temples, like men: this can be a sign of a hormonal abnormality.