The five layers of the epidermis include the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Cells in the epidermis divide and move up to replace cells in the layers above, changing as they move from one layer to the next.
The stratum basale is the layer closest to the dermis. It consists of a single layer of dividing cells. The stratum spinosum is the next layer and consists of eight to 10 layers of cells. This layer has the nickname "prickly cell layer" due to the way the cells bind to each other when they shrink. They appear to form prickles or spines.
Above the stratum spinosum is the stratum granulosum. Consisting of three to five layers, cells in the stratum granulosum begin to keratinize in order to move to the stratum lucidum. The stratum granulosum contains granules rich in lipids, providing a waterproof sealant for the skin. The stratum granulosum is sometimes accompanied by a fourth layer known as the stratum lucidum.
The final layer of the epidermis is the stratum corneum, which contains dead cells flattened into scales and packed with keratin. These dead cells flake off and are a major component of household dust.