What Does a Bed Sore Look Like at Each Stage?

Bed sores, clinically called pressure injuries, progress through a recognized series of stages that range from intact but damaged skin to deep wounds exposing muscle or bone. Each stage has a distinct visual profile, and knowing what to look for can mean the difference between catching a problem early and dealing with a wound that takes months to heal. The staging system used today was formalized by a national advisory panel and has been revised over time, but the core idea is straightforward: the deeper the tissue damage, the higher the stage.

Stage 1 Looks Deceptively Mild

A stage 1 pressure injury is the earliest visible sign of trouble, and it can be easy to dismiss. The skin is still intact with no open wound, but there is a defined area of redness that does not turn white when you press on it. In healthy skin, pressing a fingertip against a red spot causes the color to briefly blanch. When that blanching response is gone, it means blood flow in the tissue underneath has already been disrupted. The spot may also feel warmer, cooler, firmer, or softer than the surrounding skin.

Stage 1 injuries most commonly appear over bony prominences where pressure concentrates: the sacrum (lower back above the tailbone), heels, hips, and the back of the head in people who lie on their backs for extended periods. In people who sit for long hours, the ischial tuberosities (the “sit bones”) are a frequent site. The redness at this stage is sometimes mistaken for a normal reaction to brief pressure, but the key distinction is persistence. Normal redness from sitting or lying fades within minutes of relieving the pressure. Stage 1 redness lingers.

Stage 2 Breaks the Skin Surface

At stage 2, the damage has crossed from beneath the surface to a visible wound. You are looking at partial-thickness skin loss where the top layers have been destroyed, exposing the dermis. The wound bed appears pink or red and moist, and crucially, you will not see fat, muscle, or deeper structures. Stage 2 injuries can also appear as intact or ruptured fluid-filled blisters rather than an open sore. The fluid inside these blisters is typically clear or blood-tinged (serous), not pus-like.

There should be no slough, which is the yellowish or whitish dead tissue that clings to a wound bed, and no eschar, the dark, hard, leathery scab-like covering seen in more advanced wounds. If either of those is present, the injury is more severe than stage 2.¹ Stage 2 wounds heal by a process called epithelialization, where new skin cells migrate across the wound surface from the edges inward, rather than by filling in from the bottom with scar-like tissue.² This distinction matters because it means stage 2 injuries, if caught promptly, can heal relatively quickly and with less scarring.

A common source of confusion at this stage is telling the difference between a stage 2 pressure injury and skin damage from moisture, such as incontinence-associated dermatitis. Moisture damage tends to be diffuse and follows the pattern of where fluid contacts skin, while a stage 2 pressure injury is localized directly over a bony area where pressure was applied. The shape and location usually tell the story.

Stage 3 Extends Through the Full Skin Thickness

Stage 3 is the point at which the wound has eaten through the entire thickness of the skin and into the subcutaneous fat below it. You can see fat tissue in the wound, but you should not be able to see bone, tendon, or muscle. The wound may look like a shallow crater, and its edges can start to roll inward, a feature clinicians call epibole. Slough may be present in the wound bed, appearing as yellow, tan, or grayish material. Undermining, where the wound extends sideways under intact skin like a shelf, can also begin at this stage.

The depth of a stage 3 wound varies depending on where it is on the body. Over the bridge of the nose or on the ear, where there is very little subcutaneous fat, even a relatively shallow wound can qualify as stage 3. Over the sacrum or buttocks, where fat layers can be thick, a stage 3 wound may form a much deeper crater. One case report describes a paraplegic patient who presented with a stage 3 pressure injury over the ischium that had extended into deep subcutaneous tissue and was complicated by suspected systemic infection.³ At this stage, the risk of serious complications climbs considerably.

Stage 4 Exposes Bone, Muscle, or Tendon

Stage 4 is the most severe stageable wound. You are looking at full-thickness tissue loss with directly visible or palpable fascia, muscle, tendon, ligament, cartilage, or bone in the wound bed. Slough and eschar are frequently present, and the wound often has complex features like tunneling (a narrow channel extending away from the main wound), undermining, and rolled wound edges.⁴

These wounds can be startlingly large and deep. A sacral stage 4 injury, for instance, can form a cavity you could fit a fist into, with visible pelvic bone at the base. The wound may have a foul odor from colonizing bacteria and can drain significant amounts of fluid. Infection at this stage is a major concern, including osteomyelitis, which is infection of the underlying bone. Stage 4 wounds typically require months of treatment, often including surgical intervention such as debridement or flap closure, and they carry a meaningful risk of life-threatening sepsis.

Deep Tissue Pressure Injury

Deep tissue pressure injury is a category that does not fit neatly into the numbered stages because the damage starts from the inside out. Instead of progressing from a surface wound that gradually deepens, the injury begins in the muscle and soft tissue underneath intact skin and works its way to the surface. What you see from the outside is a localized area of persistent, non-blanchable discoloration that looks distinctly different from a stage 1 injury.

In people with lighter skin tones, the hallmark is a purple or maroon patch with a well-defined border, often surrounded by a ring of redness.⁵ The area may feel boggy or mushy compared to the firm tissue around it, and it can be painful even though the skin appears unbroken. The discoloration is caused by damage to deeper tissues that has not yet manifested as an open wound. Over the following days, the overlying skin may break down and the wound can evolve rapidly into a stage 3 or stage 4 injury. This makes deep tissue injury one of the most alarming findings in wound care, because what looks like a bruise on the surface can represent extensive destruction underneath.

Deep tissue injuries are particularly common over the heel, where a thin layer of tissue sits between the skin and the calcaneus bone. A patient who has been in surgery for several hours or on prolonged bedrest may develop a purple patch on the heel that seems innocuous initially but evolves into a deep cavity wound within a week.

Unstageable Wounds

An unstageable pressure injury is one where the base of the wound is obscured by slough, eschar, or both, making it impossible to determine the true depth of tissue damage. The wound bed is covered by material that ranges from yellow, tan, gray, green, or brown slough to dark brown or black eschar.⁶ Until that covering is removed through debridement, no one can say whether the wound is a stage 3 or stage 4 underneath.

Eschar on a pressure injury looks like a thick, dry, leathery cap sitting on top of the wound, often firmly adherent to the tissue below. It can be black and crusty or dark brown and slightly softer. On the heels, a special exception applies: stable, dry eschar that shows no signs of infection (no redness, warmth, tenderness, swelling, or drainage around it) is sometimes left in place as a natural biological covering rather than removed. This is one of the few situations where an unstageable wound is intentionally left unstageable.

Why Skin Tone Changes What You See

The classic descriptions of stage 1 redness and deep tissue purple-maroon discoloration were largely developed by studying lighter-skinned patients, and they do not translate well to darker skin tones. This is a well-documented problem in wound care, not a minor footnote. In people with darker skin, the redness of stage 1 may not be visible at all. Instead, the earliest sign of pressure damage tends to be a darkening of the skin beyond its usual tone, sometimes with a slightly ashen or purplish cast.⁷

Because visual detection of erythema varies so significantly with pigmentation, researchers have investigated technology-based alternatives. Infrared thermography, which detects heat patterns in tissue, identified thermal anomalies before any visual signs appeared, and its performance was consistent across all skin tones. Visual erythema detection, by contrast, was markedly less reliable in darker-skinned individuals, with lighter-skinned participants displaying much greater measurable color change.⁸ In the absence of thermal imaging equipment, which most home caregivers do not have, the practical advice is to rely on touch and the patient’s report of pain or tenderness. A spot that feels warmer, cooler, or different in texture from surrounding skin, or that the patient says hurts, should be treated as a possible stage 1 injury regardless of whether you can see color change.

Mucosal Membrane Pressure Injuries

Not all pressure injuries occur on external skin. Mucosal membrane pressure injuries develop on the moist tissue inside the body, typically where a medical device presses against a surface: inside the nostrils from an oxygen tube, on the lips from an endotracheal tube, or inside the mouth from a poorly fitting oral device. These injuries cannot be staged using the standard numbered system because mucosal tissue has a completely different anatomy than skin. There is no epidermis-dermis-subcutaneous fat layering to grade.

What you see instead is redness, swelling, erosion, or ulceration of the membrane at the device contact point. Reported incidence in hospital settings has ranged widely, from under 1% to over 30% in intensive care populations, depending on how aggressively surveillance was conducted.⁹ These injuries are easy to miss because they are hidden under or behind the device causing them. If you or someone you care for has a medical device pressing against skin or mucous membranes, it is worth periodically checking the contact site.

Why a Healing Wound Does Not “Reverse” Through the Stages

A common misconception is that as a pressure injury heals, it goes backward through the stages: a stage 4 becomes a stage 3, then a stage 2, then a stage 1, and finally disappears. This is not how the body repairs deep wounds. When a stage 4 wound heals, it does not regenerate the lost muscle, fat, and dermis. Instead, the defect fills in with granulation tissue, a mix of new blood vessels, connective tissue cells, and collagen that is structurally different from the original tissue.¹⁰ The surface eventually closes over with a thin layer of new skin, but underneath, the architecture is scar tissue rather than the original layered structures.

This is why wound care professionals do not use reverse staging. A healing stage 4 wound is documented as a “stage 4 pressure injury, healing” with a description of how the wound is progressing (shrinking dimensions, filling with granulation tissue, less drainage). Calling it a stage 2 because it is now shallow would imply that only a thin layer of skin was ever lost, which misrepresents the severity and ongoing vulnerability of the site. The tissue that fills the gap is weaker than what was there before, and the healed site remains at elevated risk for future breakdown.

How Staging Systems Vary Around the World

If you look up pressure injury staging in different countries, you may encounter slightly different terminology and numbering. The first formal classification systems appeared in the 1950s, and today several systems are in use internationally. Some countries use a four-stage system, others include the unstageable and deep tissue categories, and some use the word “grade” instead of “stage.” Despite these differences, the conceptual meaning behind the categories is comparable across systems, and no evidence indicates that one classification is clearly better than another.¹¹

In 2016, a major revision by the National Pressure Ulcer Advisory Panel updated the staging definitions used in the United States and shifted the official terminology from “pressure ulcer” to “pressure injury,” reflecting the fact that stage 1 and deep tissue injuries involve damaged but intact skin with no open ulcer. Each revised definition focuses on describing the extent of tissue loss and the anatomical features that may or may not be visible.¹² You may still hear healthcare providers use “pressure ulcer,” “pressure sore,” “bed sore,” and “decubitus ulcer” interchangeably. They all refer to the same condition.

Getting a Reliable Photo for Clinical Communication

Photographs of pressure injuries are increasingly used to communicate wound status between clinicians, especially in home care and telehealth settings. But a wound photograph taken under different lighting, angles, or camera settings can make the same wound look dramatically different in ways that affect staging and treatment decisions. Research has shown that using standardized techniques and color reference targets alongside the wound substantially reduces measured color error and improves reproducibility between photographs.¹³

If you are photographing a wound at home to share with a healthcare provider, a few practical steps help. Use consistent, even lighting, ideally daylight or a bright overhead light without heavy yellow or blue casts. Hold the camera perpendicular to the wound surface rather than at an angle. Include a ruler or measuring tape at the wound edge so the viewer can gauge size. And if possible, place a commercially available color calibration card in the frame so the clinician can mentally adjust for any color distortion. These steps are particularly important for stage 1 and deep tissue injuries, where the visual finding is a color change rather than an obvious open wound, and where subtle differences in hue carry diagnostic weight.