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February 23, 2018
Q. Humans are pretty much the only animal to have hair that grows continuously for many years yet also suffers the indignity of going bald. What else can be said of our tangled relationship with hair?
A. Our entire body, except for the palms of our hands and soles of our feet, is covered with hair, about 5 million follicles, or about the same as chimps and other primates, says John Murray in his book “How To Be Human,” as excerpted in New Scientist magazine. Terminal hair grows on the scalp, eyebrows and eyelashes; vellus hair is found everywhere else, so wispy and short as to be almost invisible. Hair follicles go through stages of growth and dormancy, with the growing stage controlled by hormones: Short, fine leg hairs grow for about two months, armpit hair for six months, and head hair nonstop for six years or more. As for pubic hair, adult humans have thicker hair around their genitals than do most primates.
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