Review note: AI-assisted draft independently checked against the cited sources by a separate AI reviewer. Not clinician-reviewed. Use with your course materials, supervised clinical training and current local policies.
Skin layers help explain pressure injury staging, but the deepest visible layer alone is not enough. First establish a pressure-related cause, then assess tissue damage and the whole wound. Pressure injuries may also occur beneath medical devices. NPIAP
Anatomy connection: See the skin layers in 3D
The layers, top to bottom
- Epidermis: the outer skin layer.
- Dermis: connective tissue beneath the epidermis, containing vessels and nerves.
- Hypodermis: subcutaneous tissue, including fat; it lies beneath the skin itself.
- Deeper structures: fascia, muscle, tendon, ligament, cartilage and bone.
The model helps locate these structures; its colors are teaching cues. OpenStax, Layers of the Skin
The stages
These summaries use the NPIAP classification described in Open RN, Pressure Injuries and the NPIAP definitions.
| Category | Key findings | 3D |
|---|---|---|
| Stage 1 | Skin remains intact, with localized non-blanchable erythema. Appearance varies with skin pigmentation. | view |
| Stage 2 | Partial-thickness loss exposing viable, moist dermis, typically pink or red; a serum-filled blister may be present. | view |
| Stage 3 | Full-thickness skin loss with visible fat, without exposure of deeper supporting structures. | view |
| Stage 4 | Full-thickness tissue loss: fascia, muscle, tendon, ligament, cartilage or bone is exposed or directly palpable. | view |
| Unstageable | Slough or eschar prevents determination of the extent of full-thickness tissue loss. | |
| Deep tissue pressure injury | Persistent non-blanchable deep red, maroon or purple change; skin separation may reveal a dark bed or blood-filled blister. |
Assessment across skin tones
Visible redness and blanching are harder to assess in darker skin. Compare the affected area with surrounding skin and assess temperature, firmness or softness, and pain. Absence of obvious redness does not establish healthy tissue. Deep tissue discoloration also varies with pigmentation. Open RN
Exam traps
- Stage 2 excludes fat, granulation tissue, slough and eschar. Do not apply this label to moisture damage, skin tears or burns.
- Fat alone does not settle the stage. Check for deeper structures and obscured tissue loss. A shallow wound is not automatically Stage 2; depth varies by site.
- Some slough does not automatically mean unstageable. The deciding issue is whether it obscures the extent of injury.
- Stable eschar on a heel or ischemic limb should not be softened or removed: stable means dry, adherent and intact, without erythema or fluctuance.
- Mucosal pressure injuries cannot be staged. Skin injuries caused by medical devices can be staged.
These distinctions follow NPIAP. A blood-filled blister warrants assessment for deep tissue injury rather than automatic Stage 2 classification. Deep tissue injuries can evolve rapidly. Open RN
Risk assessment and practice
The Braden Scale assesses risk of developing pressure injuries; it does not assign the stage of an existing wound. Open RN, Braden Scale
Practice question: A pressure-related wound has its full depth concealed by black eschar. Which category applies? Unstageable—the concealed tissue loss cannot be assigned Stage 3 or 4 from that finding alone.
Step through stage 1, stage 2, stage 3 and stage 4 to connect the categories with anatomy.
Educational content for exam preparation, written with AI using the linked sources. Clinical wound assessment and care follow facility policy and the treating team's guidance.