Bedsores, now formally called pressure injuries, are classified into four main stages based on how deep the damage extends into the skin and underlying tissue. Stage 1 involves only the skin’s surface, while stage 4 reaches as deep as bone. Two additional categories, unstageable and deep tissue injury, apply when the full extent of damage can’t yet be determined. Understanding each stage helps you recognize early warning signs and grasp why prompt action matters.
Stage 1: Skin Is Intact but Damaged
A stage 1 pressure injury is the earliest and most treatable form. The skin remains unbroken, but a patch of redness appears over a bony area like the tailbone, heel, hip, or shoulder blade. The key feature is that this redness doesn’t turn white when you press on it. On lighter skin, this is fairly easy to spot. On darker skin tones, visible blanching may not appear at all, but the area often looks different in color compared to the surrounding skin.
Beyond color changes, the spot may feel warmer or cooler than the skin around it. It can also feel unusually firm or soft, and it’s often painful or tender to the touch. A reliable way to confirm a stage 1 injury is to relieve pressure on the area: if redness persists for more than 20 minutes after you reposition, that’s a strong indicator the tissue has been damaged rather than just temporarily compressed.
Stage 1 injuries are fully reversible. Removing pressure, improving nutrition, and keeping the skin clean and dry are usually enough to resolve them within a few days.
Stage 2: The Skin Breaks Open
At stage 2, damage has pushed through the outer skin layer into the dermis, the thicker layer underneath. This shows up in one of two ways: a shallow open wound with a red or pink base, or a fluid-filled blister that may be intact or already ruptured. The wound bed won’t have any dead tissue covering it at this point, and there’s no bruising (bruising suggests deeper damage).
Stage 2 injuries are painful and need more active wound care than stage 1, but they still involve only partial thickness skin loss. With proper treatment, including keeping the wound moist, protected, and pressure-free, healing typically takes days to weeks depending on the person’s overall health.
Stage 3: Damage Reaches Below the Skin
Stage 3 marks a significant escalation. The injury now involves full thickness tissue loss, meaning the damage has eaten through the entire skin and into the fat layer beneath it. You may be able to see subcutaneous fat in the wound, but bone, tendon, and muscle are not yet visible. Dead tissue called slough (a yellowish or grayish film) may partially cover the wound bed.
These wounds can also develop undermining and tunneling, where the injury extends sideways or deeper beneath the surrounding skin, making the wound larger than it appears on the surface. Stage 3 injuries take weeks to months to heal, often require specialized wound care, and carry a real risk of serious infection. The body’s natural repair processes struggle at this depth, especially in people who are malnourished, have diabetes, or have limited blood flow to the area.
Stage 4: The Deepest and Most Dangerous
Stage 4 pressure injuries involve full thickness tissue loss with exposed bone, tendon, or muscle. Slough or a hard, dark scab called eschar may cover parts of the wound. Undermining and tunneling are common, and the wound can extend far beyond what’s visible at the surface.
These are the most life-threatening pressure injuries. Healing takes months, often requires surgery (such as skin flap procedures), and in some cases the wound never fully closes. The exposed deep structures create a direct pathway for bacteria, which is why stage 4 injuries carry the highest risk of devastating complications.
Unstageable Injuries
Sometimes a pressure injury clearly involves full thickness tissue loss, but the wound base is completely covered by slough or eschar, making it impossible to see how deep the damage goes. These are classified as unstageable. Slough ranges in color from yellow to tan, grey, green, or brown. Eschar is typically tan, brown, or black and has a leathery texture.
Until enough of this dead tissue is removed to reveal the wound base, there’s no way to know whether the injury is stage 3 or stage 4. One exception: stable, dry eschar on the heels acts as the body’s natural protective cover and is generally left in place rather than removed.
Deep Tissue Pressure Injury
This category describes damage that starts from the inside out. The skin surface may look intact or nearly so, but the tissue underneath has already been crushed by sustained pressure. It often appears as a deep purple or maroon discolored area, or a blood-filled blister. The injury can evolve rapidly, sometimes progressing to a stage 3 or 4 wound within days as the dead tissue beneath the surface breaks down and the true extent of damage becomes visible.
Deep tissue injuries are particularly deceptive because the surface appearance dramatically understates what’s happening underneath. They’re classified separately because their trajectory is unpredictable at the time of discovery.
How Stages Relate to Complications
The deeper a pressure injury goes, the more dangerous it becomes. Stage 1 and 2 injuries rarely cause systemic problems. Stages 3 and 4 are a different story entirely. They significantly increase the risk of life-threatening infections including cellulitis (a spreading skin infection), sepsis (a full-body inflammatory response to infection), and osteomyelitis (bone infection).
Some advanced pressure injuries develop sinus tracts, which are tunnel-like passages connecting the wound to deeper structures in the body. These tracts can introduce bacteria into the bloodstream, leading to conditions like bacterial meningitis, endocarditis (heart valve infection), or septic arthritis. In rare but severe cases, group A streptococcus infections can progress to necrotizing fasciitis. Amputation is sometimes necessary when infection in a limb becomes uncontrollable.
Who Is Most at Risk
Pressure injuries develop when sustained pressure cuts off blood flow to the skin and underlying tissue. People who can’t reposition themselves are at the highest risk: those who are bedridden, use a wheelchair, are recovering from surgery, or have conditions that reduce sensation (such as spinal cord injuries or neuropathy).
Healthcare providers use the Braden Scale to assess risk. It scores six factors, including mobility, moisture exposure, nutrition, and sensory perception, on a scale from 6 to 23. Lower scores mean higher risk. A score of 18 or below generally flags someone as at risk for developing pressure injuries. Poor nutrition, dehydration, thinning skin from aging, and reduced blood circulation all accelerate tissue breakdown once pressure is applied.
Why Early Detection Changes Outcomes
Pressure injuries do not skip stages going forward, but they can progress from stage 1 to stage 4 surprisingly fast, sometimes within days in vulnerable individuals. The difference between catching a stage 1 injury and discovering a stage 3 wound is often the difference between a simple repositioning fix and months of intensive wound care with serious infection risk.
Regular skin checks over bony prominences are the single most effective prevention tool, especially for the tailbone, heels, hips, and the back of the head. If you’re caring for someone with limited mobility, check these areas daily. A patch of redness that doesn’t fade within 20 minutes of pressure relief is your earliest actionable warning sign.