What are the four stages of pressure injury?

Stage 1: pressure injury is a localized area of skin, typically over a bony prominence, that is intact and nonblanchable redness. Stage 2: involves partial-thickness loss of dermis. Stage 3: involves full thickness tissue loss, in which subcutaneous fat is sometimes visible, but bone, tendon, and muscle are not exposed. Stage 4: involves full thickness tissue los with exposed bone, tendon, cartilage, or muscle.