The word decubitus comes from the Latin word "decumbere", which means to lie down. It is usually called a bed sore, pressure sore or pressure ulcer. Bed sores develop from unrelieved pressure on the skin, causing damage to the skin and the underlying skin tissue. The continuous pressure compresses small blood vessels, which cannot supply the surrounding tissue with enough oxygen and nutrients. The skin changes and becomes necrotic (dies). Bed sores mainly affect people who have to lie in bed for long periods. The most vulnerable areas are those where the skin lies directly over the bone, and include the heels, ankles, knees, hips, base of the spine, spine, and elbows. Elderly people or people with chronic diseases such as diabetes or circulation problems have a high risk of developing bed sores.