People who live with pets notice that some animals moult in the spring and fall. Losing feathers or fur is unattractive, but it leads to a beautiful new coat in which to survive the winter or to attract a mate. It turns out humans also moult.
Hair grows in a three-phase process. During the anagen phase, the tiny bud of the follicle sinks down and grows a new robust follicle underneath the shriveled follicle of the last hair. The new hair grows up alongside the old one, peeping out of the same orifice, until the old, rootless hair finally falls out.
A study, which admittedly used only Caucasian men, found that among active people who spent a great deal of time outdoors, well over 90% of their follicles were in anagen in the early spring, and by the autumn only about 80% were in anagen. The autumn also doubled the rate of shed hairs.
A second study of women in New York found that women grow more hair in the spring and moult in the fall, just like men do. And it’s not just scalp hair that undergoes these changes. Men’s beards kicked their growth up in the spring.