Q: Why is it that when men get older many of them go bald but start to grow hair in their nose and ears?
A: It is commonly believed that the increased growth of hair in the nose and ears among aging men is tied to the same causes as male-pattern baldness, which is to say dihydrotestosterone levels. This hormone, which
causes the familiar pattern of thinning and loss in the scalp, also causes the some of the vellus hairs that are naturally present in the nose and ears to grow darker, longer and grow coarser.
The hormone traditionally effects follicles that are sensitive to the hormone and therefore lends credence to the idea that this hair growth is at least predisposed genetically,
given that the levels of dihydrotestosterone and the sensitivity would both be genetic factors whose variance would account for the wide range of hairiness in the noses and ears of aging men.
The different reactions within the different hair follicles relates to the way men develop secondary sexual characteristics (which is usually governed by the levels of hormones in
the body). A common secondary sexual characteristic in men is darker, coarser body hair. So while the testosterone can result in the loss of scalp hair, it can lengthen and coarsen the hair on other parts of the body.