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Question: Testosterone/Hair loss |
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How can the hormone testosterone cause hair loss? What exactly happens in this process?
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Answer: |
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Male hormones (androgens) regulate hair growth. They have a converse effect on different regions of the body, however. Androgens stimulate the growth of long, pigmented hairs (terminal hairs) in the facial, pubic and axillary areas (also in women), but inhibit the growth of terminal hairs on the scalp. For baldness to occur though, an additional genetic predisposition is necessary. The genes involved in this process have not yet been identified.
Inside the hair follicle the male hormone testosterone is converted into an even more active hormone called dihydrotestrosterone (DHT). Even weak androgens that circulate in the bloodstream (e.g. dehydroepiandrosterone, DHEA) can be transformed into more potent androgens in the hair follicles. In the follicles of the beard these potent androgens, esp. dihydrotestosterone, cause the secretion of factors that promote cell division. In the follicles of the scalp, on the other hand, they secrete factors that impede cell division. The detailed mechanisms are not yet known.
In a person with a genetic predisposition to baldness an excessive amount of dihydrotestosterone seems to be produced in the scalp. There also seems to be a larger than average number of androgen receptors in the scalp. The response to these elevated levels of androgen is a "miniaturization" of the hair follicles which eventually leads to the loss of the large terminal hairs in the scalp.
Author:
Prof. Walter Lichtensteiger, Institut für Pharmakologie und Toxikologie, Universität Zürich, Zürich
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