Stage 1 – Nonblanchable erythema of intact skin.
Stage 2 – Partial thickness superficial skin loss involving epidermis and/or dermis that usually presents as an abrasion, blister, or shallow crater.
Stage 3 – Full thickness skin loss with damage or necrosis of subcutaneous tissue that may extend down to, but not through, underlying fascia, presenting as a deep crater with or without undermining of adjacent tissue.
Stage 4 – Full thickness skin loss with extensive destruction, tissue necrosis, or damage to muscle, bone, or supporting structures (e.g. tendon or joint capsule), and may be present with undermining and sinus tracts.