Ulcers in Dogs' Mouth: What They Look Like and Why

Yes, dogs get mouth ulcers, and any open sore you can see inside your dog's mouth should be examined by a veterinarian, because the ulcer itself is a sign rather than a diagnosis. If the sores came on suddenly and your dog may have chewed a cleaning product, a battery, an electrical cord or an irritating houseplant, call your vet or an animal poison control service such as the ASPCA Animal Poison Control Center or the Pet Poison Helpline straight away.

A mouth ulcer is a break in the lining of the mouth where the protective surface layer has been lost, leaving raw tissue exposed. They hurt. The mouth is dense with nerve endings, and dogs with oral ulceration often stop crunching hard kibble, paw at the face, or turn away when you reach for their muzzle. The reason the cause matters so much is that the list behind these sores runs from plaque on the teeth all the way to kidney disease and oral cancer, and those paths lead to completely different care. Mouth ulcers are a symptom, not a diagnosis, and the fastest route to relief is a veterinary oral exam that identifies what is driving them.

What the sores actually look like

In the earliest stage, an ulcer looks like a bright red, moist, slightly sunken patch where the normal pink, lightly pebbled surface of the gum or cheek has been rubbed away. Within a day or two many ulcers develop a yellow-grey or dull white film across the middle, which is fibrin, surrounded by an angry red rim. Some are pinpoint. Others spread into broad sheets of raw tissue along the gum line. Most bleed easily when touched, when your dog chews, or when you lift the lip to look.

Where they sit is often the most useful clue of all:

• Inner cheeks and lips, in patches that mirror the tooth they rest against. These are often called contact ulcers or kissing ulcers because the tissue kisses the plaque-covered tooth surface.
• Gum margins, right where gum meets tooth, usually alongside heavy tartar.
• Tongue tip and edges, which is a classic location for sores linked to systemic illness.
• Hard palate, under the tongue, and the corners of the mouth, common sites for burns, foreign material and trauma.

If you have been searching for photos, use them for orientation only. Appearances overlap heavily between causes, and no image can tell you whether you are looking at a simple erosion, an ulcerated mass or the oral sign of an internal disease. A photo cannot separate those. An exam can.

Symptoms owners usually notice first

Plenty of dogs are found to have oral ulcers only when someone finally looks. Before that, the signs are indirect:

• Breath that has turned strongly foul, or in some dogs faintly ammonia-like
• Drooling, sometimes thick and ropey, sometimes tinged pink or brown
• Dropping food, chewing on one side, or approaching the bowl and then backing off
• Pawing at the mouth, rubbing the face along carpet or furniture
• Becoming head shy, or flinching when touched near the muzzle
• Yelping when yawning, or holding the mouth slightly open
• Weight loss, or a sudden preference for soft food over anything crunchy
• Visible swelling, bleeding gums, or a bad taste that makes the dog lick constantly

Look for signs beyond the mouth too. Increased thirst and urination, vomiting and lethargy point toward internal disease. Crusting on the nose, eyelids or footpads points toward immune-mediated skin conditions that involve the mouth as well. Coughing or laboured breathing after chewing an electrical cord is an emergency in its own right.

What can cause ulcers in a dog's mouth

There is no single answer to why your dog has ulcers in her mouth, which is exactly why guessing at home goes badly. Below are the causes vets work through most often.

Cause	What the sores tend to look like	Other signs	How urgent
Periodontal disease and contact ulcers	Red, raw patches on the cheek or lip exactly where tissue rests against a tooth	Heavy tartar, foul breath, bleeding gums	Book a vet visit soon
Chronic ulcerative stomatitis	Widespread, deep, intensely painful ulceration along the gum line and cheeks	Severe pain, heavy drool, refusing food	Book a vet visit soon
Kidney disease and uraemia	Grey, sloughing sores on the tongue tip and edges	Ammonia-like breath, increased thirst, vomiting, weight loss	Same-day veterinary care
Caustic or chemical burns	Raw, peeling tissue on tongue, palate and lips, appearing suddenly	Sudden drooling, retching, access to a product	Emergency, call poison control
Electrical cord injury	Linear burns at the lip corners or across the tongue	Often a young dog, possible coughing or breathing trouble	Emergency
Irritant plants or insect stings	Blistered, swollen, reddened tissue after chewing	Sudden drooling, face rubbing, swelling	Same-day care or poison control
Foreign material such as grass awns, bone shards or stick splinters	One sore, often with local swelling or a draining tract	One-sided chewing, gagging, pawing	Same-day veterinary care
Immune-mediated disease	Ulcers clustered where skin meets mucosa: lips, nose, eyelids	Skin crusting, footpad lesions, lethargy	Book a vet visit soon
Oral tumours	A single ulcerated mass with a firm base that bleeds	Loose teeth, facial swelling, bloody saliva	Prompt veterinary assessment

A few of these deserve more detail.

Dental disease is the most common driver by a wide margin. Plaque is a living bacterial film, and the soft tissue pressed against it reacts. Research suggests that canine chronic ulcerative stomatitis reflects an exaggerated immune response to that plaque rather than a simple infection, which is why meticulous plaque control, and in severely affected dogs the extraction of teeth the tissue contacts, sits at the centre of how vets manage it.

Systemic illness shows up in the mouth because the oral lining turns over quickly and is unforgiving of anything that disrupts healing. Advanced kidney disease is the classic example, where waste products the kidneys can no longer clear damage the tongue surface. Ulcers in that setting are not a mouth problem with a mouth solution.

Anything that burns or cuts. Puppies chew cords. Dogs lick spilled cleaning products, gnaw sticks that splinter, and mouth plants whose sap is loaded with irritant crystals. Those injuries appear suddenly in an otherwise well dog, and sudden onset after chewing something is always worth a phone call rather than a wait-and-see night.

Masses. Any new lump in the mouth, ulcerated or not, needs a veterinary exam, and only a needle sample or biopsy can tell you what it is. No supplement, rinse or home remedy belongs in that decision.

When mouth sores need urgent attention

Some presentations should not wait for a routine appointment. Go to a veterinarian or emergency clinic if your dog has stopped eating or drinking entirely, is bleeding from the mouth, has sudden facial or tongue swelling, is retching or struggling to swallow, is showing any difficulty breathing, has visible burns, or has collapsed or become unusually dull. The same applies if you know or suspect your dog swallowed a caustic or unknown substance.

Oral ulceration also overlaps with a long list of other canine conditions, and it helps to see where it fits among them rather than treating the mouth in isolation. Pain that stops a dog eating becomes a nutritional and hydration problem quickly, especially in small, young or already unwell dogs.

How vets find the cause and what care involves

A conscious exam only goes so far, because painful mouths do not open willingly and the back of the mouth is hard to see. Expect your vet to recommend a sedated or anaesthetised oral exam with full-mouth dental radiographs if dental disease is on the table. Bloodwork and a urinalysis screen for kidney and liver disease and for inflammatory patterns. A biopsy or needle sample is the only way to characterise a mass or to confirm an immune-mediated disease, and swabs or cultures are used selectively when infection is suspected.

Treatment follows the diagnosis. That may mean a professional dental cleaning with extractions, removal of a foreign body, prescription pain control, antibiotics where they are genuinely indicated, immune-modulating medication for immune-driven disease, or management of the underlying systemic illness. Vets commonly add a prescribed oral rinse or gel and a soft-food plan while tissue recovers. Follow the medication plan you are given, and talk to your vet before changing or stopping anything, including if your dog seems much better after a few days.

Two home-care mistakes cause real harm. Never put human mouthwash, hydrogen peroxide or undiluted antiseptics in a dog's mouth. And never give human pain relievers such as ibuprofen, naproxen or aspirin, which are a frequent cause of serious poisoning in dogs.

Healing time and comfort at home

How long these sores take to settle depends entirely on what caused them. A superficial erosion from a one-off irritant often improves once the irritant is gone and the tissue is left alone. Ulcers driven by ongoing dental disease, immune disease or kidney disease persist until that underlying problem is addressed, which is why repeat courses of antibiotics without a diagnosis rarely hold. Results vary from dog to dog, so ask your veterinarian what recovery should look like for your specific case and what would count as a setback worth a call.

In the meantime, offer softened or wet food, keep fresh water constantly available, pause hard chews, bones and tug games, and skip toothbrushing over raw tissue until your vet says the mouth is ready. Keep a simple log of what your dog eats each day. Appetite is the most honest comfort score you have.

Key Takeaways

• Dogs absolutely get mouth ulcers, and the ulcer is a sign of something else rather than a condition in its own right.
• They look like raw red patches that often develop a grey-white centre and a red rim, most often on the inner cheeks, gum margins and tongue edges.
• Dental and periodontal disease is the most common cause, but kidney disease, caustic burns, foreign material, immune-mediated disease and oral tumours all appear on the list.
• Sudden sores after chewing a product, plant or cord warrant an immediate call to a vet or an animal poison control service.
• Human painkillers, mouthwash and peroxide are unsafe choices for a dog's mouth.
• Diagnosis usually needs a sedated oral exam, dental radiographs, bloodwork, and sometimes a biopsy.

Your veterinarian owns the diagnosis and the treatment plan here. An oral exam, imaging and lab work are what turn a visible sore into an answer, and everything you do at home works best when it supports that plan rather than substituting for it. If your dog has sores in her mouth today, book the exam, bring a list of what she has been chewing and how her appetite and thirst have changed, and let the findings guide what comes next.

Related reading: Dog Emergency Signs, and a broader library of canine conditions.