SYMPTOM
Mouth ulcers
Mouth ulcers are raw, red sores on the tongue, gums, palate or lips, and in a cat they are often hard to see. Owners more often notice drooling, pawing at the mouth, bad breath, difficulty eating, eating less, or a scruffier coat from reduced grooming. Cats can show few signs even with painful mouth disease.
Immune-mediated
Conditions in which the immune system targets the tissues of the mouth can produce ulceration, often affecting the gums, tongue, or palate. These patterns may appear as part of a broader immune response or remain confined to the oral cavity.
Infectious
Viral, bacterial, or fungal infections can damage the oral mucosa, leading to ulcers that may be single or multiple. The pattern often depends on the organism involved and the animal's immune response.
Metabolic
Kidney disease and certain other metabolic disturbances can lead to ulceration of the mouth, typically through the accumulation of waste products that irritate the oral tissues. These ulcers often appear alongside other systemic signs.
Traumatic or chemical
Chewing electrical cables, seen mostly in kittens, burns the tongue, lips, gums and palate, and the full extent of the damage can take several days to show. Caustic chemicals typically affect the tongue and palate, and cats are often exposed by grooming a product such as a disinfectant off their fur or paws. Chewing hard objects can also cause a single ulcer.
Neoplastic
Tumours arising in the mouth may ulcerate as they grow, creating lesions that can bleed or appear irregular. Many are invasive from the start: in cats, squamous cell carcinoma commonly involves the bone beneath the gums, and only a biopsy separates a tumour from a simple ulcer.
Dental
Severe dental disease, including advanced periodontal disease or tooth root abscesses, can lead to ulceration of adjacent soft tissues. The ulcers often sit near the affected tooth or along the gum line.
Why timing matters
Early observation
When mouth ulcers are first noticed, they may represent a recent injury, an acute infection, or the early stage of a systemic process. The animal's behaviour around food and water, the location of the ulcer, and whether there are other signs can all contribute to the picture at this stage. In some cases, early ulcers resolve as the underlying trigger is removed or as healing progresses.
Later presentation
Ulcers that persist beyond two to three weeks, recur after apparent healing, or increase in size may reflect an ongoing process rather than a self-limiting event. Chronic ulceration can accompany systemic illness, immune-mediated disease, or progressive conditions such as neoplasia. Whether the surrounding tissue is inflamed, thickened or bleeding often adds further context to the evolving picture.
Some ulcers remain stable in size and appearance, whilst others change over days to weeks. Simple traumatic ulcers tend to heal once the cause is removed, whereas those linked to systemic or immune-mediated causes may wax and wane or fail to heal without addressing the underlying process. Individual variation in healing capacity, concurrent disease, and the nature of the cause all influence the trajectory.
Conditions commonly associated
Feline Calicivirus
Calicivirus characteristically causes mouth ulcers, located mainly on the tongue, and ulcers can also appear on the lips and nose.
Feline Herpesvirus (FHV-1)
Mouth ulcers are an uncommon sign of feline herpesvirus. The usual signs are drooling, sneezing, fever, dullness, poor appetite, red eyes, and discharge from the eyes and nose.
Chronic Kidney Disease in Cats
In cats with chronic kidney disease, mouth ulcers can develop when waste products accumulate in the bloodstream and irritate the oral mucosa, a phenomenon sometimes referred to as uraemic stomatitis. These ulcers tend to appear in more advanced stages of the disease.
Acute Kidney Injury
Acute kidney injury can cause mouth ulcers through the same build-up of waste products seen in chronic disease. It develops suddenly, and the ulcers come with not eating, dullness, dehydration and often vomiting.
Dental Disease in Cats
Dental disease in cats can produce ulceration where inflamed or infected oral tissues come into contact with tooth surfaces, or where the immune response to bacterial plaque causes breakdown of the gingival margin. In some cases, tooth resorption or stomatitis may contribute to ulcer formation in the mouth.
Eosinophilic Granuloma Complex in Cats
Besides indolent ulcers on the upper lip, this complex includes eosinophilic granulomas, which can affect the lips and the inside of the mouth.
Erythema Multiforme
In more severe cases, erythema multiforme erodes the lining of the mouth, leaving painful ulcers.
Indolent Ulcer in Cats
This condition typically produces a raised, ulcerated lesion on the upper lip that can look and behave like a persistent mouth ulcer.
Toxic Epidermal Necrolysis
The same reaction that damages the skin often affects the lining of the mouth, producing painful ulcers on the gums, tongue or lips.
Stomatitis in Cats
Chronic gingivostomatitis causes severely inflamed, ulcerated and sometimes proliferative tissue, typically at the back of the mouth beside the folds at the base of the tongue, with marked pain on opening the mouth.
The page on this condition is being checked again and is offline for now.
Oral Squamous Cell Carcinoma in Cats
Squamous cell carcinoma is the most common malignant mouth tumour in cats and often affects the gums, tongue or the area under the tongue.
When to explore further
Ulcers that have been present for more than two to three weeks without signs of healing may warrant closer attention, particularly if they are changing in size or appearance, because the look of an ulcer alone does not separate a tumour from other causes.
Reduced appetite, difficulty eating, drooling or weight loss alongside ulcers show that mouth pain is affecting eating or that the illness is wider. A cat that eats little or nothing for a few days (published cases follow 2 to 7 days without food) can develop fatty liver disease (hepatic lipidosis), so the two to three week window does not apply to a cat that has stopped eating.
Multiple ulcers appearing simultaneously, or ulcers recurring after apparent resolution, can suggest an underlying condition rather than a single isolated event.
If there is bleeding from the ulcer, swelling of the surrounding tissue, or an unpleasant odour, these features may reflect infection, advanced dental disease, or tissue breakdown.
Mouth ulcers together with vomiting, dullness, not eating or a change in thirst can be a sign of kidney failure, which cannot be judged at home and is confirmed only with blood and urine tests. Acute kidney injury develops suddenly, and severe cases that need treatment have a survival rate of about 50%.
A cat seen chewing an electrical cable, or with mouth soreness after contact with a household chemical, can be more ill than its mouth shows. Electrical burns can cause life-threatening fluid on the lungs, and signs of chemical injury can take several hours to appear.
Mouth ulcers gain meaning when considered alongside the animal's broader health picture, including appetite, behaviour, and any other changes that have emerged over the same period. Documenting the appearance, location, and duration of the ulcers can be a useful reference point in conversations about the animal's wellbeing. The trajectory over the following days to weeks (whether the ulcers are healing, stable or changing) often informs how the picture is understood and what may be explored further.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS