Why do eyebrows and other bodily hair grow out of control as we get older?& We find out why we develop a post-retirement facial forest in this Question of the Week.& Plus, we ask why humans have blood types, and if any animals share this blood system with us...
In this episode
00:00 - Why does hair grow out of control in older people?
Why does hair grow out of control in older people?
We put this question to Des Tobin, Professor of Cell Biology, University of Bradford...
Hair growth is very susceptible to hormones, to the so-called sex steroid hormones: principally oestrogens and androgens. The dominant hormone for males is in the androgen category, particularly testosterone.
Surprisingly, the levels of testosterone continue to increase with age up until the age of 70. Since most male hair is responsive to androgens, with age and with increasing hormone levels you tend to get more and more vigorous hair growth, particularly in the areas that were perhaps not as robust as when the individual was younger. For example, on the nose, ears and on their eyebrows.
The nose and the ears have got thousands and thousands of hairs. They're so small you can't see them. In fact, the tip of the nose is the hairiest part of the body in terms of density of hairs per unit area.
With time, these tiny - formerly invisible - hairs can be stimulated with these male hormones, which go up with age, and can therefore become more cosmetically visible with age. The same applies for the eyebrows and for the ears.
In women, oestrogen levels drop after menopause, and their lower levels of testosterone become more engaged with the process of hair growth because they stimulate whereas oestrogens tend to inhibit.
So you're just releasing more stimulatory power from the androgens we have.