Skin protects our bodies from the outside world. Because of this, the cells of our skin are tightly connected and extremely durable. When skin cells wear out, they are replaced with new skin cells. The part of the skin that consists of dead cells is known as the stratum corneum or the horned layer. 

New skin cells are formed in the layer located below the stratum corneum. This layer is known as the epidermis.

The skin protects itself from harmful solar radiation by tanning. However, all solar radiation is not harmful. This is because the skin also uses solar radiation to produce important vitamin D. When your skin tans during the summer, the change in your skin color is not permanent, because the skin cells that have changed their color will soon die and flake away. 

The color of the cells produced by the epidermis, however, is permanent. It is an inherited characteristic that is determined by your genes. This means that if two people have a dark skin color, their children will also have a dark skin color. 

A layer of dermis is located below the epidermis. The dermis contains sebaceous glands and sweat glands. Sebaceous glands produce fat-like sebum, which protects the skin. If a sebaceous gland becomes infected, the result is a pimple. Sweat glands produce sweat. The body emits sweat when it needs to lower its temperature. The dermis also contains large numbers of receptor cells, which sense various kinds of information.