Pressure ulcers are staged based on how deep the damage extends into the skin and underlying tissue. The system uses four numbered stages plus two additional categories (unstageable and deep tissue pressure injury) for wounds that can’t be classified by depth alone. Staging requires looking at the wound bed, identifying which tissue layers are involved, and matching what you see to specific criteria established by the National Pressure Injury Advisory Panel (NPIAP).
One important note on terminology: the clinical field now uses “pressure injury” rather than “pressure ulcer” because damage can occur before the skin actually breaks open. The staging system applies the same way regardless of which term you use.
Stage 1: Intact Skin With Non-Blanchable Redness
Stage 1 is the earliest identifiable pressure injury. The skin is still intact, but there’s a localized area of redness that doesn’t turn white when you press on it with your finger. This distinction matters: if you press lightly on the red area and the color disappears momentarily, that’s called blanchable erythema, which is a warning sign but not yet a pressure injury. When the redness stays put under finger pressure, capillary damage has already occurred, and the wound is classified as Stage 1.
The affected area may also feel warmer, cooler, firmer, or softer than the surrounding skin. These texture and temperature changes can sometimes appear before any visible color change, which makes them especially important in people with darker skin tones where redness may not be visible or detectable. In those cases, look for localized swelling, pain, or changes in skin firmness and temperature rather than relying on color alone.
Stage 2: Partial-Thickness Skin Loss
At Stage 2, the surface of the skin has broken. The wound bed is visible and typically appears pink or red and moist. It may also present as an intact or ruptured fluid-filled blister. The key characteristic is that the damage stays within the upper layers of skin (the epidermis and part of the dermis) and does not extend into the fat layer beneath.
What you won’t see in a Stage 2 injury: deeper tissue like fat, muscle, or bone. You also shouldn’t see dead tissue covering the wound bed. If you do, the injury is more severe than Stage 2. Moisture-related skin damage, tape injuries, and skin tears are sometimes confused with Stage 2 pressure injuries but have different causes and shouldn’t be staged this way.
Stage 3: Full-Thickness Skin Loss
Stage 3 marks the point where damage extends through the full thickness of the skin and into the subcutaneous fat layer, but does not cross the fascia (the tough connective tissue that sits on top of muscle). You may see fat visible in the wound. Dead tissue (slough) may be present but doesn’t obscure the wound bed enough to prevent staging. The wound may have rolled edges, a condition called epibole, where the skin curls inward at the wound margin and stalls healing.
Depth varies significantly by body location. Stage 3 injuries on the bridge of the nose, ear, or shin can appear shallow because these areas have very little subcutaneous fat. On areas with more padding, like the buttocks, the same stage can produce a notably deeper wound. The wound may also be foul-smelling.
Stage 4: Full-Thickness Tissue and Skin Loss
Stage 4 is the most severe numbered stage. The wound extends past the subcutaneous fat and through the fascia, exposing or directly involving deeper structures. Bone, tendon, muscle, or joint capsule may be visible or palpable in the wound bed. Slough or dead tissue may be present in parts of the wound, but enough of the wound bed is visible to confirm the depth reaches these deeper structures.
Stage 4 injuries often include undermining (tissue destruction that extends under the intact skin edges) and tunneling (channels that extend from the wound into surrounding tissue). Because bone is exposed or involved, infection of the bone is a significant risk at this stage. Like Stage 3, the apparent depth depends on anatomy: a Stage 4 wound over a bony area with little soft tissue coverage will look different from one in a more padded region.
Unstageable: Hidden Wound Bed
An unstageable pressure injury is one where the true extent of tissue damage is unknown because the wound bed is covered by slough (yellow, tan, or gray dead tissue) or eschar (thick, black or brown dead tissue that forms a hard crust). You know the wound exists, and you know it’s at least a full-thickness injury, but you can’t determine whether it’s a Stage 3 or Stage 4 until the dead tissue is removed and the wound bed becomes visible.
Once slough or eschar is cleared, the wound can be accurately staged. Until then, it stays classified as unstageable. One exception: stable, dry eschar on the heel acts as a natural biological cover and is generally left intact rather than removed for staging purposes.
Deep Tissue Pressure Injury
Deep tissue pressure injury (DTPI) looks different from the numbered stages. The skin may be intact or broken, but there’s a persistent area of deep red, maroon, or purple discoloration. This color signals damage that started at the bone-muscle interface, deep beneath the surface, from prolonged pressure and shearing forces. The area may feel painful, firm, mushy, boggy, warmer, or cooler compared to surrounding tissue.
These injuries are unpredictable. They may evolve rapidly, with the skin breaking down to reveal the full extent of tissue damage over days. Or they may resolve without tissue loss. This category exists because the damage doesn’t follow the surface-to-deep progression of Stages 1 through 4. It starts deep and works outward. DTPI should not be used to describe injuries caused by vascular disease, trauma, nerve damage, or skin conditions.
Injuries From Medical Devices
Pressure injuries caused by medical devices, such as oxygen tubing, splints, or breathing tubes, are staged using the same system. The NPIAP formally recognized medical devices as a source of pressure injuries in 2016. The injury is staged by the same tissue-depth criteria, but the shape of the wound often matches the shape of the device that caused it.
These injuries can be harder to assess because the device often sits directly over the damaged skin, making regular inspection difficult. They also tend to develop faster than injuries over bony prominences. For injuries that occur on mucosal membranes (such as inside the mouth from an intubation tube), the standard numbered staging system doesn’t apply cleanly because mucosal tissue has a different structure than skin. These are documented as mucosal membrane pressure injuries and described by their characteristics rather than assigned a numbered stage.
What Staging Does Not Do
Staging describes the worst level of tissue damage at the time of assessment. It does not work in reverse. A Stage 4 wound that is healing does not get “downstaged” to Stage 3, then Stage 2, and so on. The body fills deep wounds with scar tissue, not with the original muscle, fat, and skin layers. A healing Stage 4 wound is documented as a “healing Stage 4,” not reclassified to a lower number.
Staging also only applies to pressure injuries. Wounds from arterial insufficiency, diabetic neuropathy, moisture damage, or surgical incisions have their own classification systems. If the wound wasn’t caused by pressure or shearing forces, this staging system doesn’t apply.
Assessing Risk With the Braden Scale
The Braden Scale is the most widely used tool for predicting who is likely to develop a pressure injury before one appears. It scores six factors: sensory perception (ability to feel discomfort), physical activity level, mobility (ability to change position), moisture exposure, nutrition, and friction or shearing forces. Each factor receives a score, and the total ranges from 6 to 23. Lower scores mean higher risk: 19 to 23 is low risk, 15 to 18 is mild, 13 to 14 is moderate, 10 to 12 is high, and 9 or below is severe risk. The scale helps guide how aggressively prevention measures need to be applied, particularly repositioning schedules and support surface selection.