Crusts are found on superficial or partial-thickness wounds. Crusting is the rusty brown, dry crust that forms over any injured surface on skin, within 24 hours of injury. Whenever our skin is injured due to any cut or abrasion, it starts bleeding due to blood flowing from the severed vessels. This blood containing platelets, fibrin and blood cells, soon clots to prevent further blood loss. The outer surface of this blood clot, dries up (dehydrates) to form a rusty brown crust, which use to be called a scab, which covers the underlying healing tissues like a cap. The purpose of a crust/scab is to prevent further dehydration of the healing skin underneath, to protect it from infections, and to prevent any entry of contaminants from the external environment. Crust generally remain firmly in place until the skin underneath has been repaired and new skin cells have appeared, after which it naturally falls off.