MEDICAL ANIMATION TRANSCRIPT: A pressure injury or ulcer is a wound caused by constant pressure on your skin. It may also be called a pressure sore, pressure ulcer, bed sore, or decubitus ulcer. Pressure injuries occur most frequently in areas where your bones are close to the skin, including your heels, ankles, hips, tailbone, or elbows. In order to understand how pressure injuries happen, it's important to know about the layers of the skin. Your skin is made up of three main layers. The top layer, called the epidermis, is a thin layer that protects your body from the environment. The thicker middle layer is called the dermis. Its main functions are to supply the epidermis with nutrients, help regulate your body temperature, and provide strength and elasticity to your skin. The innermost layer is called the hypodermis or subcutaneous layer. This layer stores fat, which cushions the muscles and bones beneath it. In a pressure injury, constant pressure on the skin over a long period of time can compress the blood vessels that supply the layers with the oxygen and nutrients they need to survive. If there's not enough blood flow, your skin tissue begins to die, and a pressure injury forms. If you have a pressure injury, your healthcare provider will classify it based on what can be known about the depth of tissue damage. This is called staging. In a Stage I pressure injury, the skin is intact, red, and inflamed. The redness is non-blanchable. This means it doesn't become pale if you press on it. A Stage II pressure injury appears as a blister or an open sore. There's partial thickness loss of the epidermis and dermis. The area surrounding the sore may be red and irritated. A Stage III pressure injury is a crater-like full-thickness loss of skin. It extends down to the fat tissue of the hypodermis. Stage IV is the most severe. A Stage IV pressure injury is a full-thickness loss of tissue. It extends through all three layers of skin and into the underlying muscle or bone. An unstageable pressure injury is a full-thickness loss of tissue. It's called unstageable because the injury is covered by dead tissue, making it hard to tell how deep it is. And a suspected deep tissue injury appears as a maroon or purple area of the skin. It may contain a blister filled with blood. It looks like this because of damaged soft tissue underneath your skin. To prevent infection in your pressure injury, your doctor will clean your wound using water and a mild soap or saline solution. If your wound is severe, your doctor will debride or surgically remove the dead tissue from the pressure injury. To protect your wound and keep it from drying out while it heals, your doctor may cover it with a specialized bandage. To find out more about pressure injuries, talk to your healthcare provider.