Generally hair, whether it is on your head or your arms, is to control our temperature. The hair on our head helps to protect the temperature of the brain. You may also notice ‘goose pimples’ on your arms when you get cold, this is actually little muscles causing your hairs to stand up which trap a layer of warm air, stopping us getting cold
Hair serves many purposes on our head; mainly warmth and sheilding from UV rays as well as protecting from impact. The hair also protects from scalp-splitting, skull cracking small injuries.