The epidermis has no direct blood supply, but instead is supported and fed by the dermis. The dermis also contains nerve endings, which let you sense heat, cold, pressure, pain, etc. These help you protect yourself from burns, punctures, and so on by warning you when there is danger to your skin. Functionally speaking, therefore the dermis is where the action is.
The epidermis is your interface to the world. It has two main layers, the inner of which is living and the outer of which is dead. The dead skin cells of the outer layer are what we can actually see, and they are constantly flaking off and being replaced by new cells being pushed outward.
The living, inner layer is called the malpighian layer. It is in direct contact with the dermis, which feeds and supports it. It is here that the sun affects the skin during tanning. The malpighian layer is itself layered like this: The bottom layer, in direct contact with the dermis, is the basal layer. Above the basal layer is the spinous layer. Above the spinous layer is the granular layer. And above the granular layer is the stratum corneum. The stratum corneum is the outer layer of dead cells, the cells that we see as our skin. The cells in this layer are filled with a very strong protein called keratin. Horns, hair, hoofs, fingernails, and feathers all gain their strength from this remarkable structure. It is the keratin that makes your skin so tough. In parts of the body that get a lot of wear, like the palms and the feet, the stratum corneum is forms much thicker layers, to handle the abrasion.
Living among the basal cells in the malpighian layer is another type of cell called a melanocyte. Melanocytes produce melanin, which is a pigment that is the source of both tanning and naturally dark skin color, such as in @African-Americans. The Encyclopedia @Britannica describes melanocytes in the following way:
"The appearance of the skin is partly due to the reddish pigment in the blood of the superficial vessels. In the main, however, it is determined by melanin, a pigment manufactured by dendritic cells called melanocytes, found among the basal cells of the epidermis. Their numbers in any one region of the body, which range from about 1,000 to more than 2,000 per square millimetre, are roughly the same within and between races; the blondest whites have as many as the darkest blacks. Color differences are due solely to the amount of melanin produced and the nature of the pigment granules.
