The epidermis is a protective outer covering of many plants and animals. It may be comprised of a single layer, as in plants, or of several layers of cells on top of the dermis, as in those of vertebrate animals. The primary role of the epidermis is to protect the more susceptible layers of the skin.
In plants, the epidermal cells secrete further protective substance (called cuticle) to prevent desiccation (water loss). A plant leaf is lined with two layers of epidermis (i.e. upper and lower): one on top of and another one below the mesophyll layer.
In animals, such as vertebrates, the epidermis is made up of several layers to protect the underneath layers from physical damage, infection, and water loss. In humans, for instance, the epidermis is made of layers such as the following: