Melanin is a natural sunscreen. Humans can increase the production of melanin by repeated exposure to the sun, but dogs do not tan. The epidermis is joined to the dermis at the basement membrane, a layer of collagen and other products of the basal cells. Collagen is a tough, durable, fibrous protein that makes up 90 percent of the dermis and provides strength to the skin. Tanned collagen from cattle skin is otherwise known as leather.
Collagen occurs in bundles.
The third component of the dermis are glycosaminoglycans molecules composed of sugar and protein. These cells keep the skin layer moist. The cells of the dermis provide a framework for blood vessels to bring oxygen and nutrients to the skin and nerves to help the dog react to and interact with his world. Blood vessels in the dermis help control Fido's body temperature. When he runs and romps and builds up body heat, the blood flow to Fido's skin increases to release the heat to the environment.