Dead cells are cells that have lost their ability to function and are no longer alive. This can happen for various reasons, such as aging, injury, or disease. In the human body, dead cells are often removed and replaced by new, healthy cells through natural processes. In the context of biology, dead cells can also refer to the outer layer of skin, known as the epidermis. This layer consists of dead skin cells that provide a protective barrier. Over time, these cells are shed and replaced by new cells from deeper layers of the skin, helping to maintain overall skin health.