A stomach ulcer typically looks like a small, round crater in the lining of the stomach, with a whitish or grayish base surrounded by red, swollen tissue. Most are less than 3 cm across, and many are closer to 1 cm. During an endoscopy (where a tiny camera is passed down your throat), the ulcer appears as a clearly defined break in the otherwise smooth, pink stomach lining, often with radiating folds of tissue converging toward the crater like spokes on a wheel.
The Crater and Its Base
The defining visual feature of a stomach ulcer is the crater itself. Unlike a superficial scratch or erosion, a true ulcer digs deeper than the stomach’s innermost lining and penetrates into the muscular layers beneath. By definition, a gastric ulcer extends more than 5 mm in diameter and breaks through the deeper tissue layers that an erosion leaves intact. That depth is what gives it the characteristic “punched out” crater look.
The base of most ulcers is covered in a whitish or grayish coating, which is a layer of dead tissue, protein, and inflammatory material the body produces in response to the wound. Less commonly, the base can appear yellowish-green. In some cases, small dark spots are visible at the base where blood vessels have been exposed or where old blood has dried. The base of a typical benign ulcer is smooth and even, sitting at a uniform depth across the crater floor.
Edges and Surrounding Tissue
The margins of a benign stomach ulcer are usually smooth, regular, and clearly defined, almost as if someone used a hole punch. The mucosa around the ulcer is red, swollen, and congested. One of the most recognizable features is the pattern of mucosal folds: they radiate symmetrically toward the ulcer base, tapering as they approach the edge. This smooth, symmetrical pattern is actually a reassuring sign, because it suggests the ulcer is not cancerous.
The surrounding tissue often looks thickened and inflamed for a zone around the crater. This ring of swelling can make the ulcer appear slightly raised at its edges, even though the center is depressed. Some ulcers also develop small bumps of granulation tissue (the body’s early repair material) at or near the crater floor, which look like tiny, reddish protuberances.
How Size Varies
Most stomach ulcers fall in the range of 0.5 to 2 cm across. An ulcer reaching 3 cm or larger is classified as a “giant” gastric ulcer, which is uncommon and carries a higher risk of complications like perforation and bleeding. Giant ulcers sometimes look quite different from smaller ones: the base may be irregular rather than smooth, and the edges can appear distorted or indented rather than neatly defined.
What a Bleeding Ulcer Looks Like
Not all ulcers bleed, but when they do, the appearance changes significantly. Doctors classify bleeding ulcers by what they see during endoscopy, and the visual categories range from dramatic to subtle:
- Active spurting or oozing: Bright red blood is visibly flowing from the ulcer base, either as a jet from an artery or as a slow ooze across the crater floor.
- Visible vessel: The bleeding has stopped, but a small, raised nub is visible at the ulcer base. This is an exposed blood vessel, and it carries a high risk of rebleeding.
- Adherent clot: A dark red or maroon blood clot sits firmly attached to the ulcer base and cannot be washed away easily.
- Flat pigmented spot: A dark or discolored spot on the ulcer floor marks where bleeding occurred. The spot can be brown, black, or dark red.
- Clean base: The ulcer floor is covered in its typical whitish-gray coating with no signs of recent or active bleeding. This is the lowest-risk appearance.
Benign vs. Cancerous Ulcers
One of the most important reasons doctors examine a stomach ulcer closely is to distinguish a benign ulcer from a cancerous one. The visual differences can be striking. A cancerous ulcer tends to have an irregular or angular shape rather than a smooth, round one. Its edges are uneven, raised asymmetrically, and may look heaped up or nodular. The base is often bumpy and uneven rather than flat. The surrounding mucosal folds, instead of tapering neatly toward the crater, appear disrupted, clubbed, fused together, or have a “moth-eaten” look.
A benign ulcer, by contrast, has a clean geometry: round or oval shape, smooth edges, an even base, and folds that radiate symmetrically. That said, visual appearance alone is not always enough to make the call. Current guidelines recommend taking tissue samples from ulcers that show any suspicious features, especially in patients at higher risk for stomach cancer. Even some cancerous ulcers can initially look benign, which is why follow-up endoscopy is standard after treatment to confirm healing.
What a Healing Ulcer Looks Like
As a stomach ulcer heals, its appearance goes through distinct stages. In the initial healing phase, the crater begins to shrink as new tissue grows inward from the edges. The angry redness of the surrounding mucosa starts to fade, though the area still looks inflamed. During the next phase, new cells proliferate rapidly across the ulcer floor, and the crater becomes shallower and smaller.
Eventually, the ulcer transitions into a scar stage. Early scars appear reddish and slightly raised, with a characteristic pattern of parallel ridges across the former crater, sometimes described as a “palisade” pattern. Over time, the scar matures into a paler, cobblestone-textured surface with tiny pits that resemble the normal stomach lining. Healing is not considered truly complete until this final cobblestone stage is reached, which can take several weeks to months depending on the ulcer’s size and cause.
What a Perforated Ulcer Looks Like
A perforated ulcer is the most dangerous visual scenario: the crater has eroded completely through the stomach wall. On imaging, this appears as a defect or cleft extending through the full thickness of the wall, sometimes with tiny gas bubbles tracking from inside the stomach out into the surrounding abdominal space. Fluid collections form around the perforation site and near the liver, often containing visible strands of inflammatory material and trapped air bubbles rather than clear fluid.
When an ulcer penetrates into an adjacent organ rather than opening into the abdominal cavity, imaging shows the gas track extending directly into that neighboring structure, surrounded by signs of inflammation. The stomach wall around the perforation site appears markedly thickened compared to normal, and the ulcer crater itself may contain a sharply defined pocket of trapped gas visible as a bright spot within the swollen wall. Perforation is a surgical emergency, and the visual evidence on imaging is often what confirms the diagnosis within minutes.