Ulcers are open sores that can form on your skin, inside your mouth, in your stomach, or on your feet and legs. What they look like depends entirely on where they are and what caused them. Some are tiny white spots you can feel with your tongue; others are deep wounds exposing tissue beneath the skin. Here’s how to identify each type by its appearance.
Mouth Ulcers
The most common mouth ulcers, called aphthous ulcers or canker sores, start as a small round yellowish bump surrounded by a red halo. Within a day or two, the bump breaks open into a shallow, “punched-out” sore covered by a loose white, yellow, or grayish membrane. Most are less than 5 mm across, roughly the size of a pencil eraser. They typically show up on the inner cheeks, lips, tongue, or soft palate.
Larger aphthous ulcers do exist and can reach a centimeter or more, but these are far less common. Regardless of size, the hallmark look is the same: a pale or yellowish center ringed by inflamed red tissue.
Stomach Ulcers
You can’t see a stomach ulcer from the outside. These are only visible during an endoscopy, where a camera on a thin tube is guided into your stomach. On screen, a peptic ulcer typically appears as a round or oval crater in the pinkish stomach lining, though some are linear or irregularly shaped. The base of the crater is often covered by a whitish or yellowish layer of tissue, and the surrounding mucosa may look red and inflamed or, in some cases, unusually pale.
The borders of a stomach ulcer can be flat and level with the surrounding tissue, or they can be raised and slightly mounded. Doctors pay close attention to irregular, raised, or undermined edges because these features can signal something more serious than a straightforward ulcer.
Signs of a Bleeding Stomach Ulcer
Since you can’t see a stomach ulcer directly, the main visual clue that one is bleeding is your stool. A bleeding ulcer in the stomach or upper small intestine produces dark, black, tarry-looking stool, sometimes described as resembling tar or coffee grounds. This color comes from blood that has been partially digested as it travels through the intestines. Bright red blood in the stool, by contrast, usually points to bleeding lower in the digestive tract.
Pressure Ulcers (Bedsores)
Pressure ulcers develop where bone presses skin against a surface for too long, such as the tailbone, heels, hips, or shoulder blades. They progress through four stages, each with a distinct look.
- Stage 1: The skin is still intact, but a localized area stays red even when you press on it and release. On darker skin tones, this may appear as a persistent blue or purple patch rather than red. The area may also feel warmer, firmer, or softer than the surrounding skin.
- Stage 2: The top layer of skin has broken open, creating a shallow pink or red wound bed. It may also look like an intact or ruptured blister. There’s no dead tissue visible at this stage.
- Stage 3: The sore has eaten through the full thickness of the skin. You may see subcutaneous fat in the wound, but no bone, tendon, or muscle. The wound may have tunneling beneath the surface.
- Stage 4: The deepest and most serious. Bone, tendon, or muscle is exposed. The wound bed may be partly covered by dark, leathery dead tissue (eschar) or wet, yellowish dead tissue (slough).
Leg Ulcers: Venous vs. Arterial
Chronic leg ulcers fall into two main categories, and they look quite different from each other.
Venous ulcers form when blood pools in the lower legs due to poor vein function. They’re characteristically located on the inner ankle or the lower calf, in the area sometimes called the “gaiter region” (where a sock or gaiter would sit). These ulcers are typically shallow with irregular, sloping borders. The skin around them often looks darkened or brownish, and the leg may be swollen.
Arterial ulcers result from poor blood flow to the extremities. They tend to appear on the toes, heel, or other pressure points of the foot. Unlike venous ulcers, arterial ulcers have well-defined, sharply “punched out” borders, as if cut with a hole punch. The wound bed is often pale or grayish because limited blood supply means less of the healthy pink or red tissue you’d expect. The surrounding skin may look shiny and hairless, and the foot may feel cool to the touch.
Diabetic Foot Ulcers
Diabetic foot ulcers often begin as a thick callus on a pressure point of the foot, such as the ball of the foot or the bottom of the big toe. Over time, the callus builds up, breaks down underneath, and opens into a sore. Because diabetes can reduce sensation in the feet, you might not notice the ulcer until the skin has visibly broken open. The wound may be surrounded by a ring of hard, thickened callus tissue, and the base can range from pink and healthy-looking to gray or black if tissue has died. Infection can develop quickly, sometimes with redness and swelling radiating outward from the wound.
Genital Ulcers
Two of the most common causes of genital ulcers look quite different. A syphilis sore (called a chancre) is typically a single, firm, round, painless ulcer with clean edges. It often goes unnoticed because it doesn’t hurt. Herpes, on the other hand, produces clusters of small, painful blisters that break open into shallow, irregular sores. Herpes lesions tend to be multiple and grouped together, while a syphilis chancre is usually solitary. Both can appear on the genitals, anus, or mouth.
What Dead Tissue Looks Like in an Ulcer
In deeper or chronic ulcers, you may see dead tissue covering part or all of the wound bed. This tissue comes in two forms. Eschar is dry and leathery, ranging in color from tan to brown to black. It can feel hard or crusty. Slough is the wet version: soft, stringy, or gel-like tissue that’s typically yellow, tan, gray, green, or brown. When either type covers the wound completely, it’s impossible to tell how deep the ulcer actually goes without removing the dead tissue first.
What a Healing Ulcer Looks Like
A healthy healing ulcer develops granulation tissue, which appears as small, bumpy, pink or red tissue filling in the wound bed. It looks moist and slightly shiny, almost like tiny beads of tissue. This is a good sign. The wound is rebuilding itself from the bottom up. Over time, the edges of the ulcer will gradually pull inward as new skin grows to close the gap.
In the mouth, healing tissue around an extraction site or oral wound may look white or pinkish. As long as there’s no increasing pain, swelling, or foul smell, this is normal granulation tissue doing its job.
Signs an Ulcer May Be Infected
Regardless of location, an infected ulcer shares certain visual warning signs. The skin around the wound becomes increasingly red, swollen, and warm. Pus may appear in the wound bed or drain from it, and that pus can range from white to yellow, green, pink, or brown. It usually has a foul smell. The wound itself may seem to be getting larger rather than smaller, and the pain typically worsens rather than improves. Streaks of redness extending outward from the wound are a particularly urgent sign that infection is spreading beyond the ulcer itself.