Why do old men go bald, but get hairy nostrils? © Getty Images

Why do men go bald from the top of their heads?

Top of your head as shiny as a bowling ball? A male sex hormone might be responsible, causing tightening of head tissue eventually impacting the hair follicles.

Asked by: Sarah Lambert

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Characterised by hair loss from the top and front of the head, ‘male-pattern hair loss’ is partly determined by genetics and partly by high levels of a male sex hormone called dihydrotestosterone (DHT).

The most recent hypothesis suggests that the hair loss process begins during puberty, when growth of the skull and the muscles in the forehead and neck increases the tension in a tight band of tissue stretching over the top of the head. The more DHT there is, the more these muscles contract, which causes inflammation and brings in more DHT. Over time, the DHT thickens the band of tissue, restricting the supply of blood and nutrients to the hair follicles above it. The follicles on top of the head get smaller and eventually disappear, while those on the sides of the head remain largely unaffected.

However, this theory is still a work in progress. Some experts believe that DHT impacts the hair follicles directly. And DHT itself remains something of a mystery, being responsible for hair growth – not loss – on the face and in the armpits and pubic areas.

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