Pressure from prolonged positioning is a major cause of pressure ulcers. Pressure cuts off blood flow to the skin and underlying tissue, which can lead to cell death and skin breakdown if not relieved. Specific causes of pressure include leaving a patient in one position too long, using a hard or lumpy mattress, or pressure from medical devices like splints or casts. Friction and shearing forces from careless pulling or moving of a patient can also damage skin. Poor nutrition, moisture from incontinence, and lack of cleanliness further contribute to pressure ulcer development.