They are usually caused by sitting or lying in one position for too long. This puts pressure on certain areas of the body. The pressure can reduce the blood supply to the skin and the tissues under the skin. When a change in position doesn't occur often enough and the blood supply gets too low, a sore may form. Pressure sores are also called bed sores, pressure ulcers and decubitus ulcers.
Pressure sores can be serious, depending on how much of the skin and tissues have been damaged.
You should call your doctor if you think a sore is forming. Mild damage causes the skin to be discolored, but a sore doesn't form. In light-skinned people, the damaged skin may turn dark purple or red. In dark-skinned people, the area may become darker than normal. The area of damaged skin may also feel warmer than the surrounding skin.