What is formed by dead cells over a wound or blemish during healing?

The formation that occurs over a wound or blemish during the healing process is referred to as a scab. A scab forms when blood clots together to prevent further bleeding and create a protective barrier over the injury site. It comprises dried blood, serum, and other debris, which provides a temporary seal that facilitates healing beneath the surface.

While a crust can also refer to a layer that forms over the skin, it denotes a different context, often associated with conditions like acne or crusting lesions, rather than the direct closure of a wound. A scar is the permanent mark left after a wound has fully healed, which involves collagen deposition and tissue remodeling, while a callus is a thickened area of skin that develops in response to friction or pressure, not a response to healing.

Understanding these distinctions helps clarify why a scab is the correct answer in the context of wound healing, as it specifically refers to the protective layer formed immediately over a healing injury.