Pressure injuries are injuries to the skin and underlying tissue. They can range from mild reddening of the skin to severe tissue damage—and sometimes infection—that extends into muscle and bone. Pressure injuries are described in the following stages.

• Stage 1 pressure injuries are not open wounds. The skin may be painful, but it has no breaks or tears. The skin appears reddened and does not blanch (lose colour briefly when you press your finger on it and then remove your finger). In a dark-skinned person, the area may appear to be a different colour than the surrounding skin, but it may not look red. Skin temperature is often warmer. And the stage 1 injury can feel either firmer or softer than the area around it.
• Stage 2 pressure injuries are open wounds. The skin breaks open, wears away, or forms an ulcer, which is usually tender and painful. The wound expands into deeper layers of the skin. It can look like a scrape (abrasion), blister, or a shallow crater in the skin. Sometimes this stage looks like a blister filled with clear fluid. At this stage, some skin may be damaged beyond repair or may die.
• Stage 3 pressure injuries extend through the skin into deeper tissue and fat but do not reach muscle, tendon, or bone.
• Stage 4 pressure injuries extend to muscle, tendon, or bone.
• Unstageable pressure injuries are when the stage is not clear. In these cases, the base of the wound is covered by a layer of dead tissue that may be yellow, grey, green, brown, or black. The doctor cannot see the base of the wound to determine the stage.
• Deep tissue pressure injuries are when there isn't an open wound, but the tissues beneath the surface have been damaged. The area of skin may look purple or dark red, or there may be a blood-filled blister. If you or your doctor suspect a pressure injury, the area is treated as though a pressure injury has formed.

Serious complications, such as infection of the bone (osteomyelitis) or blood (sepsis), can occur if pressure injuries progress.