Determination of pressure ulcer stage is based on the severity of tissue damage to the outer and inner layers of skin, Mayo Clinic explains. Staging also depends on wound color and the degree of exposure of the underlying structures. For example, at stage 1 the skin is unbroken and red, discolored, tender or painful. The affected skin does not blanch or lighten with contact, and the skin may feel warmer or cooler than the surrounding area.
In stage 2, pressure ulcers are shallow open wounds with partial loss of tissue thickness, the National Pressure Ulcer Advisory Panel states. The wound may have a red or pink bed, a ruptured or fluid-filled blister, or a dry or shiny shallow bed. In stage 3, underlying fat is visible, and dead skin may collect on the wound. Fatty body areas are vulnerable to further tissue destruction deep beneath the visible wound.
Stage 4 involves exposure of bone, muscle or tendons, according to Mayo Clinic. Dead skin surrounds the wound, and the damage may affect deep layers of healthy skin. The advisory panel also classifies some pressure ulcers as unstageable because the wound surface is too obscured by dead tissue to gauge the extent of the damage. Deep-tissue injury is another classification in which the unbroken skin has purple or maroon discoloration and contains a blood-filled blister. The skin may also have a firm or malleable texture.