Ulcers on dogs can appear in several places, and each type looks different. A skin ulcer is an open, crater-like sore where the surface tissue has broken down, exposing raw, reddened or pink tissue underneath. But dogs also develop ulcers on their eyes, inside their mouths, and in their stomachs, each with its own set of visual clues. Here’s how to identify each type.
Skin Ulcers
A skin ulcer on a dog is deeper than a typical scrape or scratch. Rather than just removing the top layer of skin, an ulcer extends down through the full thickness of the skin and sometimes into the tissue beneath it. You’ll see an open wound with defined edges, often surrounded by reddened or discolored skin. The center may appear raw and pink, or it can look yellow or grey if dead tissue is present. Some ulcers weep fluid or produce a discharge that forms crusts around the wound edges.
Where the ulcer appears on your dog’s body often hints at the cause. Ulcers on the nose can take very specific shapes: a deep, V-shaped or wedge-shaped sore on the center groove of the nose points to a blood vessel disorder, while a linear crack along the side of the nostril suggests a different vascular condition. Immune-related diseases like lupus often produce ulcers on the nose that start with loss of pigment, then progress to open sores covered with thick crusts, eventually leaving scarring and permanent color changes. Cancerous growths like squamous cell carcinoma can appear as a firm nodule on the nose that breaks open, ulcerates, and bleeds.
Some skin ulcers start as fragile, fluid-filled blisters that rupture almost immediately, leaving behind raw erosions covered with bloody crusts. Others begin as areas of inflammation that worsen over time, developing fissures, draining tracts, or loss of the skin’s normal texture and architecture.
Pressure Sores
Dogs that are immobile, elderly, or recovering from surgery can develop pressure ulcers (also called decubital ulcers) over bony areas like elbows, hips, and hocks. These are graded on a four-stage scale:
- Grade I: A dark reddened area that doesn’t lighten when you press on it. The top layer of skin may start to peel away.
- Grade II: Full-thickness skin loss, exposing the fatty tissue underneath.
- Grade III: The sore extends through the fat layer down to the deeper connective tissue. The wound edges may be undermined, meaning the damage extends beneath apparently intact skin.
- Grade IV: The ulcer reaches all the way down to the bone, with possible bone infection.
Skin Ulcers vs. Hot Spots
Hot spots are a common source of confusion. These are weepy, wet, red patches that can appear bloody when fresh and dry and scabby as they heal. They look alarming but are self-inflicted: a dog can chew or scratch one into existence in as little as 10 minutes. Hot spots have very clear, sharp margins separating them from normal surrounding skin. A true ulcer, by contrast, tends to develop more gradually, has deeper tissue loss, and isn’t caused by the dog’s own scratching. That said, about 30% of wounds that initially look like hot spots turn out to be something else entirely, including deeper infections, bite wounds, or immune-related ulceration.
Eye (Corneal) Ulcers
Corneal ulcers are harder to see at home because the damage is on the clear surface of the eye. The most reliable sign is squinting. Some dogs barely open the affected eye, while others show only mild squinting or excessive blinking. You may also notice heavy tearing or watery discharge streaming from the eye.
A healthy cornea is perfectly clear. When an ulcer develops, the eye’s surface can turn hazy or cloudy, sometimes with visible redness. Your vet confirms the diagnosis using a special fluorescent dye dropped onto the eye. The dye sticks to any area where the outer layer of the cornea is damaged, making the ulcer glow bright green under a blue light. Without this test, many corneal ulcers are invisible to the naked eye.
Indolent “Boxer” Ulcers
A specific type of corneal ulcer, sometimes called a “Boxer ulcer,” deserves its own mention because it looks and behaves differently. Despite the name, it occurs in nearly every breed, though Boxers may be especially prone. These ulcers are always superficial, never extending into the deeper layers of the cornea, but they refuse to heal on their own. They can persist for weeks or months.
The hallmark feature is loose, peeling edges of tissue around the ulcer. When the fluorescent dye is applied, it seeps underneath these loose edges and creates a distinctive “halo” pattern, with a ring of green stain surrounding the main ulcer. Over time, you may also see tiny blood vessels growing into the cornea from the edges and a foggy, swollen appearance to the tissue around the sore. These ulcers are never infected, which distinguishes them from other non-healing eye wounds.
Mouth Ulcers
Oral ulcers are easy to miss because most owners don’t regularly look inside their dog’s mouth. What you’re more likely to notice first are the indirect signs: bad breath, drooling, reluctance to eat, or bleeding from the mouth.
If you can get a look inside, mouth ulcers appear as red, raw, open sores on the gums, inner lips, or tongue. One characteristic pattern in dogs is the “kissing ulcer,” which forms where the inside of the upper lip rests against the large canine or premolar teeth. The constant contact between lip and tooth creates matching sores on the lip surface. Dogs with stomatitis (widespread mouth inflammation) develop severely inflamed gums that may recede, along with large sores near the surfaces of the bigger teeth.
Fungal infections produce open, bleeding sores on the tongue or the lining of the mouth. A more severe condition called necrotizing ulcerative gingivitis causes tissue death along the gumline, with ulceration that can spread across the inner mouth and, in bad cases, expose the underlying bone.
Signs of Stomach Ulcers
You can’t see a stomach ulcer from the outside, but the signs it produces are visible. In a study of 82 dogs with gastrointestinal ulcers, 88% had vomiting, 32% vomited blood, and 31% had dark, tarry black stools. That dark stool color, called melena, happens when blood from the ulcer is digested as it passes through the intestines. It looks distinctly different from normal stool: black, sticky, and tar-like rather than brown. Vomit containing blood may look bright red if the bleeding is fresh, or it can resemble dark coffee grounds if the blood has been partially digested in the stomach.
What Healing Looks Like
If your dog is being treated for a skin ulcer, knowing what healthy healing looks like can save you unnecessary worry. Within a couple of days, the wound should start producing granulation tissue, which is moist, bright pink or red tissue that gradually fills in the wound from the bottom up. It bleeds easily when touched and can look startling if you’re not expecting it. Many owners mistake it for exposed muscle, but it’s actually a sign that healing is progressing normally.
The wound will also shrink over time as the edges pull inward, a process called contraction, allowing new skin to eventually cover the surface. Full maturation of a healing wound starts around two to three weeks in but can take months to complete. Granulation tissue is generally not painful, since nerves grow into it late in the healing process. A healing wound should stay moist. If it becomes dry, develops a foul smell, or the surrounding skin turns increasingly red or swollen, those are signs of complications rather than normal healing.