Hair is made up of a protein called keratin (the same protein as in nails) produced in hair follicles in the outer layer of skin. As follicles produce new hair cells, old cells are pushed out through the surface of the skin. The visible hair is in fact a string of dead keratin cells. Each follicle has a life cycle that can be influenced by age, disease, and other factors: Anagen (active hair growth) which lasts between 2 to 6 years. Catagen (transitional stage) which lasts two to three weeks, and Telogen (resting phase). At the end of the resting phase (two to three months) the hair is shed and the growing cycle begins again to make new hair to replace it.