Why Do Men Have More Body Hair Than Women Do?

Testosterone, the male sex hormone (androgenic hormone) is responsible for the distinguishing characteristics of the masculine body and the female sex hormone namely estrogen is responsible likewise for the feminine body.

In a foetus the sex organ develops from the newly organised genital ridge. If the foetus is a male the male chromosome causes the genital ridge to secrete testosterone, which decides the development of foetal testes and if the foetus is a female the female chromosome causes this ridge to secrete estrogen, which decides the development of female gonads (ovaries).

In male foetal testes the testosterones begin to elaborate at about the seventh week of embryonic life, during which the development of male body characteristics, including the formation of a penis and scrotum rather than the formation of clitoris and a vagina occurs.

The testosterone production increases rapidly under the stimulus of anterior pituitary gonadotropic hormones at the onset of puberty and lasts throughout most of the remainder of life, but dwindling rapidly beyond the age of 50 and gradually becoming 20 to 50 per cent of the peak value by the age of 80.

The re-initiation of testosterone secretion after puberty causes the increase in size of the male genital organ eightfold before the age of 20 years. In addition it also causes the `secondary sexual characteristics' of the male beginning at puberty and ending at maturity. One among the secondary sexual characteristics is the distribution of body hairs.

Beard appears, hairline on scalp (on the top of the head) recedes anterolaterally, pubic hair grows with male pattern (triangle with apex up), hair appears in axillas. .

Although body hair is increased by androgens, scalp hair is decreased. So there is possibility of development of baldness in man who has large quantity of androgenic hormones.

The testosterone secretion rate is 4-9 mg/ day in normal adult males resulting in the plasma testosterone level as 300-1000 nanogram/ decilitre (ng/dl), which is only 30-70 ng/dl in adult woman.

This is the only reason for the presence of more body hair in men than in women.

Published in The Hindu on June 20, 2002.