A skin ulcer on a dog is an open wound where the full thickness of the outer skin layer has been lost, exposing the tissue underneath. Unlike a simple scrape or scratch, ulcers penetrate deeper than the surface and can signal anything from a bacterial infection to an autoimmune disease, a tumor, or even a metabolic disorder. Because the list of possible causes is long and the treatments vary dramatically depending on the diagnosis, a skin ulcer that does not heal within a week or two of basic wound care almost always warrants a veterinary workup.
What a Skin Ulcer Actually Looks Like
People sometimes use “ulcer” loosely to describe any raw-looking spot on their dog’s skin, but in veterinary dermatology the term has a specific meaning. An erosion is a shallow defect that removes only part of the outermost skin layer; an ulcer goes deeper, breaking through the full epidermis and sometimes reaching the tissue below it. The practical problem is that telling the two apart by eye can be genuinely difficult. Deeper erosions and shallow ulcers look almost identical on a living, moving dog, and a definitive distinction often requires a biopsy examined under a microscope.1BSAVA Library. An approach to erosions and ulcerations
What you will typically notice at home is a patch of missing fur with a moist, red, or raw-looking center. Some ulcers ooze clear fluid or pus. Others develop dark crusts or bloody scabs that keep reforming after you clean them. The surrounding skin may be swollen, warm, or discolored. Location matters too: ulcers on the footpads cause obvious limping, while those around the mouth or nose can interfere with eating and breathing. Any wound that repeatedly opens, refuses to scab over, or gradually gets larger is behaving like an ulcer rather than a normal healing cut.
Bacterial Infections and Deep Pyoderma
The single most common reason a dog develops skin ulcers is a bacterial skin infection, or pyoderma. Dogs with allergic skin disease are especially prone because chronic itching and scratching damage the skin barrier, giving bacteria an easy entry point. The usual culprit is a bacterium called Staphylococcus pseudintermedius, which lives harmlessly on healthy dog skin but can cause serious trouble once the barrier is compromised.2PubMed Central. Antimicrobial use guidelines for canine pyoderma by the International Society for Companion Animal Infectious Diseases (ISCAID)
When infection stays near the surface, you see pimple-like bumps, flaking, and redness. When it pushes deeper into the skin layers, that is deep pyoderma, and it gets uglier: bloody crusts, draining tracts, swelling, nodules, and ulcers. Deep pyoderma can also involve streptococci, gram-negative bacteria, and anaerobes in roughly four out of ten cases, which is why veterinarians often culture the wound before choosing an antibiotic.3PubMed Central. Antimicrobial use guidelines for canine pyoderma by the International Society for Companion Animal Infectious Diseases (ISCAID) Left untreated, bacteria can penetrate even deeper, reaching the fat layer and connective tissue beneath the skin. In severe cases, necrotizing infections (sometimes called flesh-eating bacteria) can develop and become life-threatening.4PubMed Central. Common superficial and deep cutaneous bacterial infections in domestic animals: A review
Parasitic Causes Worth Knowing About
In parts of the world where sandflies are common, including southern Europe, Central and South America, and parts of Asia and Africa, a parasite called Leishmania can cause skin ulcers in dogs. Canine cutaneous leishmaniasis produces a range of skin changes: scaly, flaky patches; raised nodules; and ulcers, particularly around the nose and limbs.5PubMed. Cutaneous involvement in canine leishmaniosis due to Leishmania infantum (syn. L. chagasi) Dogs can sometimes show only skin lesions without the systemic illness that leishmaniasis typically causes, which can make it trickier to diagnose if the vet is not looking for it.6PubMed. Canine cutaneous leishmaniasis caused by neotropical Leishmania infantum despite of systemic disease: A case report
This matters beyond your dog’s health: infected dogs also serve as a reservoir for the parasite and can contribute to human transmission of cutaneous leishmaniasis.7PubMed Central. Canine cutaneous leishmaniasis If you live in or have traveled with your dog through an endemic region and your dog develops chronic, non-healing skin sores, mention the travel history to your vet. It can change the diagnostic approach entirely.
When the Immune System Attacks the Skin
Some of the most dramatic ulcers in dogs come not from outside invaders but from the dog’s own immune system. Pemphigus vulgaris is a rare autoimmune disease in which the body produces antibodies that attack the proteins holding skin cells together. The cells separate, fluid-filled blisters form, and those blisters quickly rupture into deep erosions and shallow ulcers. In a review of 54 cases, 93% of dogs with pemphigus vulgaris had lesions affecting the mouth, lips, or the junction between mucous membranes and skin.8PubMed Central. Deep pemphigus (pemphigus vulgaris, pemphigus vegetans and paraneoplastic pemphigus) in dogs, cats and horses: a comprehensive review If your dog’s ulcers are concentrated around the gums, lips, eyelids, or nostrils, autoimmune disease belongs on the list of suspects.
A related condition, pemphigus foliaceus, is more common but tends to produce crusting and superficial erosions rather than deep ulcers. Veterinary studies have also documented ear-tip vasculitis and other autoimmune skin disorders in dogs, though these remain relatively uncommon, affecting well under one percent of dermatology cases in at least one large clinical review.9Indian Journal of Veterinary Pathology. Clinicopathological evaluation of Autoimmune skin diseases in dogs Autoimmune skin ulcers do not respond to antibiotics, and treating them requires immunosuppressive drugs, which is why getting the diagnosis right matters so much.
Tumors That Break Through the Skin
Not every skin ulcer is an infection or an immune problem. Some are cancer. Squamous cell carcinoma is one of the most frequently diagnosed skin tumors in dogs, and it can present as a non-healing ulcer, particularly on areas with little pigment and sparse hair. Dogs that spend a lot of time in direct sunlight are at higher risk, especially on the belly, inner thighs, and nose where the skin is lightest.10PubMed. Sunlight-skin cancer association in the dog: a report of three cases Mast cell tumors, melanomas, and other skin cancers can also ulcerate as they grow through the overlying skin.
The key warning sign is a wound that simply will not close despite appropriate care, especially in an older dog. If a lesion has been present for weeks, slowly expanding, and not responding to antibiotics or topical treatment, a biopsy is the only way to rule out or confirm a tumor. Early detection changes outcomes significantly, because some skin cancers in dogs are curable with surgery when caught before they spread.
Metabolic and Nutritional Links
A less well-known cause of skin ulcers in dogs is hepatocutaneous syndrome, also called superficial necrolytic dermatitis. This condition is linked to severe liver disease or, less often, a glucagon-producing pancreatic tumor. The skin lesions are distinctive: crusting, redness, and painful ulceration concentrated on the footpads, face, and areas where the skin meets mucous membranes. Footpad ulceration can be severe enough to cause outright lameness.11Journal of Veterinary Internal Medicine. Long-Term Management with Adipose Tissue-Derived Mesenchymal Stem Cells and Conventional Treatment in a Dog with Hepatocutaneous Syndrome
What makes this condition especially tricky is that the skin lesions may appear before anyone realizes the dog has liver problems. A vet seeing footpad ulcers and facial crusting together in a middle-aged or older dog will often check liver enzymes and run an abdominal ultrasound to look for the characteristic “honeycomb” pattern in the liver. The prognosis depends heavily on the underlying cause, but recognizing the skin signs early can lead to quicker intervention.
Burns, Pressure Sores, and Physical Damage
Dogs can develop ulcers from purely physical causes too. Thermal burns are an underappreciated problem, particularly in the southwestern United States and other hot climates. Dogs that lie on sun-heated pavement or metal surfaces can develop dorsal thermal necrosis: the skin on the back and sides develops redness, hair loss, ulceration, and in severe cases, full-thickness dead tissue requiring surgical removal.12PubMed Central. Dorsal thermal necrosis in dogs: a retrospective analysis of 16 cases in the southwestern USA (2009-2016)
Pressure sores, or decubital ulcers, are another physical cause, particularly in dogs that are immobile after surgery, paralyzed, or simply very large and heavy. The skin over bony prominences like the shoulder joint, hip, and ribs is most vulnerable because body weight compresses the blood supply. Thin dogs face the highest contact pressures over those areas, which is why padding matters so much for post-surgical or immobile patients. Pressure-relieving mats can significantly lower the forces on those at-risk zones compared to standard bedding.13PubMed. Comparison of the different supports used in veterinary medicine for pressure sore prevention
Vaccine-site reactions, though uncommon, represent another physical cause worth mentioning. A small subset of dogs develops ischemic dermatopathy at injection sites, where blood flow to the skin is reduced and the tissue gradually breaks down. This can cause hair loss, crusting, and ulceration on the ear tips, around the eyes, over bony prominences, and at the paw pads, sometimes appearing weeks to months after vaccination.14PubMed. Vaccine-induced ischemic dermatopathy in the dog These reactions are rare and should not discourage vaccination, but they are worth recognizing because they look very different from a typical infection and require different treatment.
Breeds With Inherited Vulnerabilities
Certain breeds are genetically predisposed to conditions that cause skin ulcers. Collies and Shetland Sheepdogs can develop familial dermatomyositis, a hereditary disease that resembles juvenile dermatomyositis in humans. Affected puppies develop skin lesions as early as seven to eleven weeks of age, concentrated on the face, lips, ears, and skin overlying bony prominences on the limbs, feet, sternum, and tail tip. Biopsy of these lesions shows vesicles, pustules, and ulcers.15PubMed Central. Familial canine dermatomyositis. Initial characterization of the cutaneous and muscular lesions The disease also affects the muscles, leading to difficulty eating or swallowing in severe cases.
Short-coated, light-skinned breeds like Dalmatians, Bull Terriers, and white Boxers are more vulnerable to sun-induced skin damage and squamous cell carcinoma. Deep-chested, large breeds are more prone to pressure sores when recuperating from orthopedic surgery. And breeds with heavy skin folds, such as Bulldogs and Shar-Peis, tend toward chronic skin fold infections that can progress to ulceration. Knowing your breed’s vulnerabilities does not prevent problems, but it can help you and your vet reach a diagnosis faster.
How Vets Figure Out the Cause
Because skin ulcers in dogs have so many possible origins, diagnosis is rarely straightforward. Your vet will typically start with a thorough history: when the lesion appeared, whether it is spreading, whether your dog has been itching, and whether the dog is on any medications or has traveled recently. The location and pattern of the ulcers give important clues. Ulcers concentrated around the mouth and nose point toward autoimmune disease. Ulcers on the footpads and face together raise the possibility of a metabolic condition. Ulcers in areas of thin fur and light skin suggest sun damage.
From there, the workup usually involves some combination of skin cytology (pressing a slide against the wound to look at cells under a microscope), bacterial culture and sensitivity testing, skin biopsy for histopathology, and sometimes blood work or imaging. Biopsy is the single most informative test for ulcers that are not clearly infectious, because it can distinguish between autoimmune blistering diseases, tumors, vascular problems, and other causes that look similar on the surface. If infection is present, culture and sensitivity testing identifies which bacteria are involved and which antibiotics will work, an increasingly important step given the rise of resistant bacteria.
The Antibiotic Resistance Problem
If your dog has a skin ulcer caused by a bacterial infection, the choice of antibiotic is no longer as simple as it once was. Methicillin-resistant Staphylococcus pseudintermedius (MRSP) has emerged as a serious challenge in veterinary medicine and continues to spread globally.16PubMed. Meticillin-resistant Staphylococcus pseudintermedius: clinical challenge and treatment options In one study of dogs treated for pyoderma, about 40% initially had MRSP on skin cultures, and roughly 45% of dogs whose pyoderma was caused by MRSP still carried the resistant bacteria on their skin even after the infection had clinically resolved.17PubMed. Prevalence of meticillin-resistant Staphylococcus pseudintermedius (MRSP) from skin and carriage sites of dogs after treatment of their meticillin-resistant or meticillin-sensitive staphylococcal pyoderma
Methicillin resistance often comes bundled with resistance to additional classes of antibiotics, which limits treatment options and makes deep infections harder to clear.18PubMed Central. Methicillin-resistant Staphylococcus pseudintermedius: epidemiological changes, antibiotic resistance, and alternative therapeutic strategies This is a major reason veterinary dermatologists now emphasize topical therapy, such as antiseptic shampoos and sprays, for surface infections whenever possible, reserving systemic antibiotics for deep infections where they are genuinely needed. Researchers are also investigating novel approaches including antimicrobial peptides, nanoparticles, and bacteriophages as potential alternatives to conventional antibiotics, though these are not yet widely available in clinical practice.19PubMed Central. Methicillin-resistant Staphylococcus pseudintermedius: epidemiological changes, antibiotic resistance, and alternative therapeutic strategies
Wound Care and Topical Options
Regardless of the underlying cause, managing the ulcer itself matters. Open wounds on dogs heal through a combination of new tissue filling in from below and new skin creeping inward from the edges. In experimental wound models, the tongue of new epithelium advancing from the wound margin measured about 0.2 mm at day four, 0.4 mm by day eight, and 0.7 mm by day fourteen.20Veterinary Dermatology. An evaluation of methods for the assessment of healing of open wounds in the dog That is slow progress, which is why even properly treated ulcers can take weeks to fully close.
Keeping the wound clean and moist is the foundation. Gentle flushing with saline or dilute chlorhexidine removes debris and bacteria without damaging the fragile new tissue. Your vet may apply wound dressings that maintain moisture while absorbing excess fluid. A controlled trial comparing wound products for first-intention healing in dogs found that a hyaluronic acid and collagen-based product achieved significantly better cosmetic scores and smaller wound areas compared to untreated controls, while manuka honey did not show a significant cosmetic benefit over the control group.21MDPI (Veterinary Sciences). First-Intention Incisional Wound Healing in Dogs and Cats: A Controlled Trial of Dermapliq and Manuka Honey That is worth knowing because manuka honey has a strong reputation in wound care, and its underwhelming performance in this particular trial is a reminder that popular does not always mean proven.
For ulcers that are slow to close, veterinarians sometimes use negative pressure wound therapy, which applies controlled suction through a sealed dressing to pull the wound edges together and promote blood flow. Low-level laser therapy is another option that has shown some promise. In a case-control study of dogs with sterile inflammatory paw lesions, laser-treated sites showed significantly better clinical scores by day four and day twenty compared to untreated control sites, with no adverse effects reported and more than half of treated lesions remaining clear at a two-month follow-up.22PubMed Central. Low-level laser therapy: Case-control study in dogs with sterile pyogranulomatous pododermatitis
Practical Steps Before and After the Vet Visit
If you spot what looks like an ulcer on your dog, a few immediate steps can help. First, prevent your dog from licking or chewing the area. Saliva introduces bacteria and constant licking slows healing. An Elizabethan collar (the cone of shame) is unfashionable but effective, and inflatable alternatives are more comfortable for some dogs. Second, gently clean the wound with saline or plain warm water. Avoid hydrogen peroxide, rubbing alcohol, or other household antiseptics at full strength, as these can damage healthy tissue. Third, do not apply over-the-counter antibiotic ointments designed for humans without checking with your vet first, because some ingredients that are safe for people are toxic to dogs if licked off.
At the vet visit, the most useful thing you can bring is a timeline. When did you first notice the lesion? Has it grown? Has your dog been scratching more than usual? Any recent changes in food, environment, or medications? Has the dog traveled or spent time outdoors in unusual settings? These details narrow the differential diagnosis faster than any single test. Take a photo of the lesion when you first notice it so you and your vet can track changes over time, especially if the visit ends up being scheduled a few days out.
After diagnosis, follow-through is where many cases stall. Antibiotic courses for deep pyoderma can run four to eight weeks or longer, and stopping early because the skin looks better is one of the most reliable ways to breed resistant bacteria and set up a relapse. Autoimmune conditions require long-term immunosuppressive therapy with regular blood monitoring. And if the cause turns out to be something environmental, like sun damage or pressure sores, prevention becomes the treatment: provide shade, limit midday sun exposure, invest in orthopedic bedding for large or immobile dogs, and keep skin folds clean and dry in susceptible breeds.