SYMPTOM
Red, swollen gums or oral tissues
Visibly inflamed, reddened, or swollen gums, or areas of redness and tissue proliferation deeper in the mouth, sometimes noticed when the animal yawns, eats, or during oral inspection.
Periodontal disease
Inflammation and infection of the gum tissues surrounding the teeth is one of the most common causes of red, swollen gums. Plaque accumulation along the gumline triggers an inflammatory response that produces gingivitis — redness and swelling of the gum margins. As periodontal disease advances, the inflammation extends deeper, potentially involving the tooth root attachments and surrounding bone. The severity can range from mild marginal redness to severely inflamed, bleeding, and receding gums.
Stomatitis
In cats particularly, an exaggerated immune response to oral antigens can produce severe, widespread inflammation of the oral mucosa that extends well beyond the gumline to affect the tissues at the back of the mouth, the tongue, palate, and lips. Feline chronic gingivostomatitis produces intensely red, swollen, and often ulcerated tissues that cause significant pain and difficulty eating. The inflammation in stomatitis is characteristically more severe and widespread than typical periodontal disease.
Tooth resorption
Feline odontoclastic resorptive lesions — a common dental condition in cats where the tooth structure is progressively destroyed by the body's own cells — can produce localised gum inflammation and tissue proliferation over the affected tooth. The gum tissue may appear to grow over or around the resorbing tooth, creating red, raised areas that can be tender to touch. This condition is extremely common in cats, with prevalence increasing with age.
Oral masses or growths
Benign and malignant growths within the oral cavity can appear as areas of tissue proliferation, redness, or swelling in the gums or oral mucosa. Epulides (benign gum masses) in dogs, squamous cell carcinoma, fibrosarcoma, and melanoma can all present as visible changes in the oral tissues. Masses may be smooth or irregular, firm or friable, and may ulcerate as they enlarge.
Eosinophilic granuloma complex
This group of inflammatory conditions, most common in cats, can affect the oral mucosa and lips, producing raised, red, and sometimes ulcerated lesions. Eosinophilic granulomas in the mouth may appear as firm, raised, yellowish-pink masses, while indolent ulcers typically affect the upper lip. These conditions are thought to have an immune-mediated or allergic basis and may wax and wane over time.
Infectious
Viral, bacterial, and fungal infections can produce oral inflammation. Feline calicivirus and herpesvirus can cause oral ulceration and gingivitis. Bacterial infections secondary to wounds, foreign bodies, or immune compromise can produce localised or generalised oral inflammation. In some geographic regions, fungal infections may involve the oral cavity, producing granulomatous lesions.
Why timing matters
Early observation
Early gum inflammation may present as a thin red line along the gum margins, mild puffiness of the gum tissue, or a slightly darker colour than normal. These subtle changes may be noticed during a veterinary dental examination or by observant owners who regularly check their pet's mouth. At this early stage, the inflammation may be limited to the gum margins adjacent to the teeth (marginal gingivitis) and may respond to professional dental cleaning and improved oral hygiene. Early gingivitis is generally reversible if the underlying cause is addressed.
Later presentation
As oral inflammation progresses, the redness and swelling become more obvious and may extend beyond the gumline to involve broader areas of the oral mucosa. The tissues may become friable (easily bleeding), ulcerated, or show proliferative changes where the tissue appears to grow excessively. In cats with stomatitis, the back of the mouth may become intensely inflamed, with the caudal oral mucosa appearing angry red and swollen. At this stage, the animal typically shows obvious signs of oral pain — difficulty eating, drooling, pawing at the mouth, and changed behaviour.
The trajectory of oral inflammation depends on its cause. Simple gingivitis from plaque accumulation may stabilise or slowly worsen depending on the level of oral hygiene. Stomatitis in cats tends to progress over time, with periods of relative stability punctuated by inflammatory flare-ups. Tooth resorption-related inflammation may slowly worsen as the resorptive process advances. Oral masses typically enlarge over time, producing progressively more tissue disruption. The rate of change provides important context — rapid onset or sudden worsening may suggest different processes than slow, gradual progression.
Conditions commonly associated
Stomatitis in Cats
Stomatitis is characterised by severe, widespread inflammation of the oral mucosa, producing intensely red, swollen gums and caudal oral tissues that extend well beyond the typical gingivitis pattern.
Dental Disease in Cats
Dental disease in cats frequently involves gingival inflammation, with gingivitis presenting as red, swollen gum tissue along the tooth margins.
Dental Disease in Dogs
Gingivitis and periodontal disease in dogs commonly present with red, inflamed gum tissue, particularly visible along the gum line adjacent to affected teeth.
Periodontal Disease
Gingivitis and periodontitis cause visible inflammation of the gum tissue, particularly along the tooth margins.
Feline Stomatitis
Feline stomatitis characteristically involves intensely inflamed, proliferative tissue of the gums and particularly the caudal oral tissues behind the teeth.
When to explore further
Gum redness or swelling that persists beyond two weeks, particularly if it involves areas beyond the gum margins adjacent to teeth, suggests an ongoing inflammatory process that may benefit from oral examination.
Oral inflammation accompanied by changes in eating behaviour — reluctance to eat hard food, dropping food, eating on one side, or reduced appetite — suggests that the condition is causing sufficient discomfort to affect the animal's ability to eat comfortably.
Bleeding from the gums, particularly spontaneous bleeding or bleeding triggered by minimal contact during eating, indicates tissue fragility from significant inflammation or pathology.
The appearance of raised, irregular, or proliferative tissue in the mouth — as opposed to simple redness and swelling — warrants closer examination to determine whether the changes represent inflammatory proliferation, tooth resorption coverage, or a mass.
Progressive worsening of oral inflammation despite home dental care measures, or gum changes accompanied by worsening breath odour, drooling, or weight loss, suggests a condition that may require professional assessment.
Regularly checking the oral cavity during calm moments — gently lifting the lips to observe the colour and condition of the gums, and noting any changes in breath odour — provides a baseline understanding of what is normal for each individual animal. Observing eating behaviour, noting any changes in food preferences or eating speed, and monitoring body weight all contribute to a broader picture of oral comfort and health.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS