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Understanding the skin

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The skin has two layers - the epidermis and the dermis. Beneath the dermis is a layer of fat, and then the deeper structures such as muscles, tendons, etc.
The epidermis has three main types of cell.

Basal cells. These are the bottom layer of cells in the epidermis.
Keratinocytes. These cells are in layers above the basal layer. They make a substance called keratin which is a hard 'waxy' material. Keratinocytes are constantly dividing and a certain number are dying at any given time. The top 'horny' layer of the epidermis is made of dead keratinocytes which contain keratin. The top of the skin is constantly being shed and replaced by new dead cells which contain keratin.
Melanocytes. These cells are dotted about at the bottom of the epidermis. They make a pigment called melanin when the skin is exposed to sun. The melanin is passed to the nearby skin cells to protect them from the sun's rays. Melanin causes the skin to tan in fair skinned people. Dark skinned people have more active melanocytes.