Do people moult seasonally?

15 March 2009

Question

Do humans moult like other hairy animals such as cats and dogs? In other words, does our hair get thicker in winter while we moult in the summer? If we don't moult, did we once have this function and have we since lost it through evolution?

Answer

We put this to Des Tobin, Associate Dean for Research at the School of Life Sciences, University of Bradford:

For most animals, like rodents you have a clear-cut wave of hair growth where all the follicles are synchronised. Moulting requires synchronicity in the follicles because the hair grows in a cycle of growth that we call anagen and a resorbative phase called catagen. In the human there is quite a bit of synchronicity in the very early stages: before birth and in the neonatal phase but it breaks up very quickly so that you get what we call a mosaic form of hair growth. Each follicle is an autonomous mini organ. Whilst, to some extent that can be re-synchronised, for example, when women are pregnant because they change their hormonal stimulus. Some studies have been done way back on hair on the thigh. I don't know why they chose thigh hair to check the seasonality of hair but it was shown that in certain times of the year perhaps a little bit related to weather (although with humans you have to be very careful because of the fact that we're wearing clothes for a very long time and we don't need it for the same thermo-regulation that mammals would have) but there is some kind of very minor peaks. If we were to do hair counts we tend to see more shedding as we go into the summer period than going into the winter period.

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