Why is blood needed in the dermis but not in the outer cells of epidermis?

Blood is needed in the dermis to supply nutrients and oxygen to the living cells and to remove waste products, as the dermis contains vital structures like blood vessels, nerves, and glands. In contrast, the outer cells of the epidermis are primarily composed of dead keratinized cells that do not require a blood supply for their function. These cells are generated in the deeper layers of the epidermis and gradually move upward, eventually dying and forming a protective barrier for the skin. Thus, only the living layers of skin, such as those in the dermis, require blood flow.