The tough, outermost sub-layer of the epidermis, made of cells that are continually shed, is the:

The stratum corneum is the tough, outermost sub-layer of the epidermis, made up of flattened, keratinized (hardened) cells that are continually shed and replaced. It provides the skin's primary protective barrier. The deepest epidermal layer, the stratum germinativum (basal layer), is where new cells are produced and where melanin is made. As cells move toward the surface they harden and eventually slough off. Understanding the basic sub-layers of the epidermis, especially the protective stratum corneum, is part of skin science.