Humans, like most mammals, have several different kinds of hair, which typically cover most regions of the body except the soles of the feet and the palms of the hands. Hair is most densely found, however, on the scalp, where it also generally grows to the greatest lengths. Though continually shed and replenished, human hair may grow a half-inch or more per month. The constant cycle of hair loss undergone by humans is often not noticeable because each follicle carries out its processes independently, generally maintaining a constant number of hairs on the head. Shedding is pronounced in certain other mammals, however, because their hair follicles may act in sync, causing pronounced hair loss or molting at certain times of the year.