A bed sore starts as a patch of skin that stays red (or purple on darker skin) and doesn’t lighten when you press on it. As it worsens, it can progress from intact but discolored skin to an open wound, a deep crater exposing fat, or in the most severe cases, a wound deep enough to reveal muscle or bone. Knowing what each stage looks like helps you catch the problem early, when it’s still reversible.
The Blanching Test: Your First Check
Before a bed sore fully develops, you can test a suspicious area with a simple finger press. Push down on the reddened or discolored spot for a few seconds, then release. In healthy skin, the area turns white under pressure and returns to its normal color within a few seconds. If the spot stays red and doesn’t lighten at all, blood flow to that area has already been compromised. That non-blanchable redness is the hallmark of a Stage 1 pressure injury.
If redness fades within 30 minutes of removing pressure from the area (by repositioning), the skin is reacting normally. If the discoloration persists beyond 30 minutes, damage has begun.
Stage 1: Skin Is Intact but Discolored
At this earliest stage, the skin isn’t broken. On lighter skin, the area looks persistently red. On darker skin tones, classic redness is often invisible. Instead, the area may appear purple, bluish, or unusually shiny. These color differences are one of the main reasons early bed sores get missed on people with dark skin, sometimes dismissed as a simple bruise.
Beyond color, a Stage 1 sore often gives tactile clues. The spot may feel noticeably warmer or cooler than the surrounding skin. It can feel firmer or harder in some cases, or oddly soft and “boggy,” as though there’s fluid trapped underneath. Localized pain or tenderness at a pressure point, even without visible skin changes, is another early warning sign that applies to all skin tones.
Stage 2: Broken Skin, Blisters, or Shallow Wounds
A Stage 2 bed sore means the top layer of skin has broken down. What you’ll see is a shallow, open wound with a pink or red base. It can also appear as an intact or ruptured blister filled with clear fluid. Some Stage 2 sores look like abrasions or scrapes. The wound is still relatively superficial at this point, involving only the upper skin layers, and you won’t see fat or deeper tissue.
This is the stage where most people first realize something is wrong, because the skin damage is now clearly visible. The area around the wound is often tender and may be slightly swollen.
Stage 3: A Deep Crater
At Stage 3, all layers of skin have been destroyed. The sore looks like a deep, bowl-shaped crater. You may be able to see yellowish fat tissue at the base of the wound, but bone, tendon, and muscle are not yet visible. The wound may contain slough, which looks like a yellow or tan stringy material on the wound surface.
Stage 3 sores can also develop tunneling, where the damage extends sideways beneath the intact skin surrounding the visible wound. This means the sore is larger underneath than it appears on the surface. Undermining (a pocket of space between the wound base and the wound edge) is also common.
Stage 4: The Most Severe
A Stage 4 bed sore is a full-thickness wound where bone, tendon, or muscle is exposed and directly visible. These are deep, often large wounds that can extend into joint capsules or other structures. Dark, leathery tissue called eschar (dead tissue that looks black or brown and crusty) may cover parts of the wound bed. Slough can also be present. Like Stage 3 sores, tunneling and undermining are common.
Sometimes a wound is clearly deep but covered entirely by eschar or slough, making it impossible to see the base. These are classified as “unstageable” because you can’t tell how deep the damage goes until the dead tissue is removed.
Deep Tissue Injury: Damage From the Inside Out
One pattern that catches people off guard is a deep tissue pressure injury. The surface skin may look intact but shows a persistent, deep purple or maroon discoloration, or there’s a blood-filled blister. Underneath, the tissue has already been crushed by sustained pressure. The area often feels boggy, painful, or warmer than the surrounding skin. Over the following days, this type of injury can rapidly deteriorate, with the skin breaking down to reveal a Stage 3 or Stage 4 wound beneath. It’s essentially a sore that formed deep in the tissue and worked its way outward.
Where Bed Sores Typically Form
Bed sores develop over bony areas where pressure concentrates. The specific location depends on body position. For someone lying on their back, the most vulnerable spots are the back of the head, the shoulder blades, the lower back (sacrum), and the heels. For someone lying on their side, the hips, inner knees, and ankles are at greatest risk. People who spend long hours in a wheelchair tend to develop sores on their sit bones (the bony points you feel when sitting on a hard surface) and tailbone.
Elbows and ears are also common sites. A wound that appears over a bony prominence and has a circular or regular shape is a strong indicator of a pressure injury specifically, rather than irritation from another cause.
Bed Sore vs. Moisture Damage
Not every red, raw area on the skin is a bed sore. Moisture-associated skin damage, often caused by prolonged contact with urine, stool, or sweat, can look similar but has distinct differences. Moisture damage tends to appear as diffuse, scattered redness rather than a single defined spot. The edges are irregular and blurry rather than distinct. It’s typically superficial and never develops black, dead tissue. You’ll also often see the surrounding skin looking white or waterlogged (macerated) from prolonged wetness.
A pressure injury, by contrast, sits over a bony prominence, has distinct edges, and tends to form a single, well-defined wound. It can develop dead tissue (black or dark brown patches) and progress to deep, full-thickness damage. Redness from a pressure injury is concentrated in one spot, while redness from moisture is spread across a broader, uneven area. Linear redness confined to the crease between the buttocks, for example, is more likely moisture damage than a pressure sore.
Signs of Infection
An existing bed sore can become infected, and the visual changes are usually noticeable. Watch for increasing redness that spreads outward from the wound edges into the surrounding skin, green or yellow discharge with a foul smell, and new warmth or swelling around the sore. The wound bed itself may change color or develop a greenish tint. Fever, increasing pain, or a wound that was improving but suddenly worsens are also warning signs that infection has set in.
How Quickly They Develop
Bed sores can begin forming in a matter of hours under sustained, unrelieved pressure, particularly in people with limited mobility, poor circulation, or thin skin. The progression from Stage 1 to a more serious wound varies widely. Some early sores reverse within days once pressure is removed. Others, especially in people with poor nutrition or reduced sensation (such as those with spinal cord injuries), can deteriorate rapidly if the pressure continues. The key factor is whether the cause, sustained pressure on vulnerable skin, is identified and relieved before deeper tissue damage takes hold.