In the most blunt terms possible, the fur, or hair, of all mammals is made up of both the protein keratin and dead skin cells. Growing from the dermis, or inner layer of the skin, dogs depend on their fur (sometimes hair) often much more than humans to regulate body temperature. Most dogs have three types of fur, called their undercoat, guard hair and whiskers. The undercoat lies closest to the dog’s skin, growing in clusters from a single follicle. This usually has a soft appearance, and helps protect the dog from cold weather.