Risk factors for the occurrence of pressure ulcers include mechanical factors, reduced skin resistance, systemic malnutrition or edema. 1. Mechanical factors: prolonged bed rest will cause local tissue pressure and increase the probability of pressure ulcers. 2. Reduced skin resistance: when the skin is often in a moist environment, friction and other stimuli, it is very easy to reduce the resistance of the skin, resulting in pressure ulcers. 3. Systemic malnutrition or edema: malnutrition is the internal cause of pressure ulcers. The skin of malnourished patients is more easily damaged and wound healing is more difficult. It is common in patients with prolonged fever, old age, edema, paralysis, coma and malignant disease. Therefore, it is important to turn over and change the body position to reduce the production of pressure sores.