Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: Villem on 21/06/2008 19:57:44

Title: Apart from testosterone, what else causes baldness?
Post by: Villem on 21/06/2008 19:57:44
Villem asked the Naked Scientists:

Question: I have heard that high testosterone level causes men to go bald, and therefore wonder whether this high level causes any other changes in say mood, behaviour, stamina etc? In other words, are bald men different in other (measurable) ways than just hairstyle.

Thanks in advance, Villem

What do you think?
Title: Apart from testosterone, what else causes baldness?
Post by: chris on 22/06/2008 10:43:37
Anything that damages or alters the activity of the hair follicle in the scalp can trigger hair loss.

Follicles are specialised collections of cells that produce the keratin filaments which we call hair. The follicles are not continuously active and have three growth phases which vary in length depending upon where on the body surface they are. These three phases are the anagen phase, when the follicle is actively producing a hair, a catagen phase during which growth stops and the hair falls out, and a thelogen phase when the follicle rests before recommencing growth.

The relative lengths of these phases can alter depending upon the role of the follicle, and this governs the ultimate length of the resulting hair. So a pubic hair has an anagen phase lasting a few weeks, and eyelash a week or so and a head-hair several years.

Part of this behaviour is genetically hard-wired into the follicle, but some is also under hormonal or metabolic control. Malnutrition, low protein intake and decreased thyroxine levels, for instance, which contribute to a  reduced metabolic rate can contribute to reduced hair growth and hair thinning.

Testosterone, on the other hand, promotes hair follicle activity in some parts of the body - in the pubic regions and on the face, but cause progressive destruction of scalp follicles. The mechanism for this latter effect is poorly understood but seems to involve a derivative of testosterone, because drugs that inhibit testosterone metabolism - like finasteride which is used to treat prostate enlargement - can also prevent hair loss.

Other conditions that can damage hair follicles and lead to hair loss include inflammatory conditions - like certain autoimmune conditions, stress (alopecia), drugs (chemotherapy) and ionising radiation (radiotherapy). In these latter two cases this is down to the rapidly dividing cells that produce hairs being affected by the therapy, which cannot discriminate between highly active cancer cells and healthy tissue.