Because epithelial tissue is capable of regeneration.
The skin consists of two tissues: the outermost, the epidermis, resting on a vascularized connective tissue, the dermis. In the epidermis, which includes several layers of cells, the outer layer is formed of dead cells that are desquamating and are constantly being replaced by proliferating basal cell cells. So, under normal physiological conditions, the epidermis, like all the epithelia, is in constant renewal. On the other hand, when accidentally, the upper parts of the epidermis are damaged as a result, for example, of a burn or a slight abrasion, the destroyed portion is regenerated thanks to an accelerated proliferation of basal epidermal cells.