A person with a decubitus ulcer has a crater-like sore on the skin, caused by pressure against the skin.

Skin ulcers form when the blood supply is decreased to a portion of the skin. Decubitus ulcers form when constant pressure against the skin reduces the blood supply. Without blood supply, the skin will not heal. Decubitus ulcers are more common in skin that lies over bones. The elderly are at greatest risk for pressure sores.