# Mouth Cancer and Ulcers in Cats: Causes and Signs

Mouth cancer in cats usually starts as squamous cell carcinoma, a tumor of the cells that line the gums, tongue, and throat. What causes cat mouth cancer is not fully settled, but genetics, viruses, and long-term mouth inflammation all appear to play a role. Ulcers and sores have many other causes too, and most of them are not cancer.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

## Quick Answer

- The most common oral cancer in cats is squamous cell carcinoma, and it often shows up first as a non-healing sore, bad breath, drooling, or trouble eating [1].
- Mouth ulcers in cats are more often caused by inflammation, infection, injury, or immune disease than by cancer [2].
- Any sore that has not healed in 1 to 2 weeks needs a veterinary exam, because early oral disease is much easier to treat than advanced disease [2].
- Cats hide mouth pain well, so weight loss, dropping food, and pawing at the face are meaningful clues [1].
- Diagnosis usually requires an exam under sedation plus a biopsy, since the vet cannot tell cancer from inflammation by looking alone.

## What a Cat Mouth Sore Looks Like and What Is Normal

A healthy cat mouth is pink, moist, and smooth. The gums meet the teeth in a clean line. There is no odor beyond mild "cat breath," no drooling, and no swelling along the jaw.

A problem may look like a red patch, a white or yellow crater, a raised lump, a bleeding spot, or a raw area where the gum pulls away from a tooth. Sores can sit on the gums, the tongue, the inside of the lips, the roof of the mouth, or far back near the throat. Some are easy to see. Others hide under the tongue or behind the last molars.

Signs that often travel with a sore include bad breath, drooling (sometimes blood tinged), dropping food, chewing on one side, and flinching when the face is touched [2]. Cats may paw at the mouth or resist having it examined [2]. Lymph nodes under the jaw can feel enlarged [2].

Bad breath alone is a common early clue. If your cat's breath has changed and stayed that way, [Cat Bad Breath: When Is It a Sign of Illness?](/knowledge/veterinary-medicine/vet-visit-decisions/cat-bad-breath-when-to-worry) walks through what different odors can mean.

## Main Causes of Mouth Sores and Cancer in Cats

Causes fall into a few broad groups. Some are common and treatable. Some are serious. A few are cancer.

### Inflammatory and Immune Causes

Gum disease is the most common oral problem in cats [2]. When plaque sits on the teeth, the gums become inflamed, and severe inflammation can progress to ulcers and loose teeth. This is why [Dental Disease In Dogs And Cats](/knowledge/veterinary-medicine/dental-care/dental-disease-in-dogs-and-cats) matters even when the mouth looks fine from the outside.

Some cats develop immune-mediated disease, where the body's own defenses attack the mouth lining [2]. This can cause painful, stubborn ulcers that come and go. Chronic gingivostomatitis, a severe widespread inflammation of the gums and back of the mouth, falls in this group.

### Infectious Causes

Several viruses can inflame the mouth in cats, including feline herpesvirus, feline calicivirus, feline leukemia virus, and feline immunodeficiency virus [2]. Calicivirus in particular is known for causing tongue and mouth ulcers. These infections are common in cats from shelters or multi-cat homes, and they often flare during stress or illness.

### Injuries, Chemicals, and Burns

Cats can burn or cut their mouths on electrical cords, hot food, caustic household products, or sharp objects [2]. Chewing on a splintered bone or a sharp toy can leave a wound. These injuries usually have a clear trigger and heal with supportive care, but deep or infected wounds need treatment.

### Metabolic and Treatment-Related Causes

Kidney disease, diabetes, and other metabolic problems can lead to mouth ulcers. Radiation therapy for tumors in the head or neck can also cause painful mouth inflammation [2]. If your cat is being treated for another condition and develops mouth sores, tell your vet right away.

### Cancer

Squamous cell carcinoma is the most common oral cancer in cats and accounts for up to 80% of oral cancers [3]. It usually affects older, non-pedigree cats, with no clear sex or breed pattern, and it most often starts in the gums, under the tongue, or on the tongue itself [1]. Other oral tumors exist, including a rare bone-origin variant called primary intraosseous squamous cell carcinoma, which can appear as a swelling of the jaw [4]. Squamous cell carcinoma has also been reported, very rarely, in the windpipe of a cat [5].

### What Causes Cat Mouth Cancer?

The honest answer is that no single cause has been proven. Research points to a mix of factors [1]:

- **Genetics.** Mutations in genes such as TP53, a gene involved in controlling cell growth, have been found in feline oral squamous cell carcinoma [3]. These mutations overlap with those seen in human head and neck cancer [6].
- **Viruses.** Papillomavirus has been studied as a possible contributor, though a direct cause-and-effect link is not confirmed [7][1].
- **Environment.** Exposure to tobacco smoke and certain chemicals has been examined as a risk factor, again without proof of direct causation [7][1].
- **Chronic inflammation.** Long-standing mouth inflammation may raise the risk over time [1].
- **Oral bacteria.** Cats with oral squamous cell carcinoma have different mouth bacteria than healthy cats, with less diversity and shifts in which species dominate [8]. Whether this is a cause or a result of the tumor is not yet known.

In short, what causes cat cancer in the mouth is likely a combination of inherited susceptibility, viral exposure, environment, and ongoing inflammation, not one single trigger [1].

### Cause Comparison

| Cause | Typical clues | How urgent |
|---|---|---|
| Gum disease | Red gum line, tartar, bad breath, drooling | Routine visit, sooner if eating changes |
| Viral infection (calicivirus, herpesvirus) | Tongue or mouth ulcers, sneezing, eye discharge, fever | Same-day to 24 hours if not eating |
| Immune-mediated disease | Recurring painful ulcers, red swollen gums, weight loss | Within a few days |
| Injury, burn, or chemical | Known exposure, sudden onset, visible wound | Same day, emergency if bleeding or swelling |
| Metabolic disease | Ulcers plus drinking, urinating, or weight changes | Within a few days |
| Squamous cell carcinoma | Firm non-healing sore, jaw swelling, foul breath, dropping food | Within days, do not wait weeks |
| Other rare tumors | Jaw swelling, loose teeth, facial asymmetry | Within days |

## Red Flags That Mean Emergency Care

Some signs cannot wait. Go to an emergency clinic now if your cat:

- Cannot swallow or is gagging continuously
- Has heavy bleeding from the mouth
- Has swelling under the jaw or around the eye that is growing fast
- Is breathing with an open mouth or making noisy breathing sounds
- Collapses, seems disoriented, or has a swollen, painful face

Call your vet the same day if your cat:

- Has stopped eating or drinking for more than 24 hours
- Drops food, cries while eating, or chews only on one side
- Has a sore that has not healed in 1 to 2 weeks
- Has foul breath that appeared suddenly
- Is drooling constantly or pawing at the face

A cat that stops eating can become dangerously ill within a day or two, especially if it is older or has another health condition.

## What You Can Safely Do at Home While Waiting

You cannot diagnose or treat a mouth sore at home. What you can do is keep your cat comfortable and gather information for the vet.

- **Offer soft, room-temperature food.** Warm food smells stronger and may encourage eating, but heat can sting an open sore. Try pate-style canned food or moistened kibble.
- **Do not touch the sore.** Poking or pressing can cause pain, bleeding, and infection.
- **Do not give human pain relievers.** Common over-the-counter drugs like ibuprofen, acetaminophen, and aspirin are toxic to cats. Your vet will calculate a safe dose based on your cat's weight and health.
- **Do not use human mouthwash, gels, or antibiotic ointments** in or near the mouth.
- **Keep a simple log.** Note when the sore appeared, what it looks like, whether your cat is eating, drinking, and using the litter box, and any bad breath or drooling. Photos taken in good light help the vet see change over time.
- **Remove hazards.** Put away electrical cords, caustic cleaners, and sharp objects your cat might chew.
- **Keep the mouth clean gently.** If your cat tolerates it, wipe the outside of the lips with a soft damp cloth. Do not force the mouth open.

If your cat is coughing or gagging along with mouth signs, [Cat Coughing and Gagging: Causes and Urgency](/knowledge/veterinary-medicine/vet-visit-decisions/cat-coughing-and-gagging) explains when those signs point to something beyond the mouth.

## What Your Veterinarian Will Check and Test

Your vet will start with a full physical exam, including the mouth, jaw, and lymph nodes under the chin [2]. A complete oral exam should be part of every routine physical, because oral disease is easiest to treat when caught early [2].

Because cats rarely hold still for a thorough look at the back of the mouth, many vets recommend an exam under sedation or anesthesia. This allows a proper look at the tongue base, the back of the throat, and under the tongue, where tumors often hide [1].

Tests your vet may recommend:

- **Dental radiographs (X-rays)** to see the tooth roots and jawbone. Bone invasion is common with oral squamous cell carcinoma [1].
- **Blood work and urinalysis** to check for kidney disease, diabetes, and other metabolic causes.
- **Fine needle aspiration or biopsy.** A biopsy is the only way to confirm cancer. A small sample of the sore is sent to a lab.
- **Viral testing** for feline leukemia virus and feline immunodeficiency virus if infection is suspected [2].
- **Imaging of the chest** to check whether a tumor has spread, since oral squamous cell carcinoma can spread to other sites [1].
- **Advanced imaging** such as CT in some cases, to plan treatment.

Ask your vet these questions directly:

1. Does this look like inflammation, infection, or a tumor?
2. Do we need a biopsy, and when?
3. Is sedation or anesthesia needed for a full exam?
4. If it is cancer, what stage is it, and what are the treatment options?
5. What signs should make me call you right away?

Treatment depends on the cause. Gum disease and inflammation are managed with dental cleaning, antibiotics, pain control, and sometimes immune-suppressing medication. Viral ulcers are treated supportively. Cancer treatment may involve surgery, radiation, or chemotherapy, and the outlook for oral squamous cell carcinoma is often poor because most cats are diagnosed late [1][6].

## Prevention and Monitoring

You cannot prevent every mouth problem, but you can catch many early.

- **Brush your cat's teeth** with pet-safe toothpaste, or use dental wipes if brushing is not tolerated. Start slowly and reward calm behavior.
- **Schedule dental cleanings** as your vet recommends. [Prevent Dental Problems In Cats](/knowledge/veterinary-medicine/dental-care/prevent-dental-problems-in-cats) covers home care in more detail.
- **Check the mouth monthly.** Lift the lips, look at the gums, and sniff the breath. Most cats accept this if you go slowly.
- **Know your cat's normal.** A cat that always has mild breath odor is different from one whose breath changed last week.
- **Keep viral risks low.** Keep vaccinations current and limit contact with unknown cats if your cat is at risk.
- **Reduce smoke exposure.** Do not smoke indoors around your cat, since tobacco smoke is one of the environmental factors studied in oral cancer [7].
- **Book twice-yearly exams for senior cats.** Older cats are the group most affected by oral squamous cell carcinoma [1].

If you have a cat with a known rodent ulcer (a specific type of lip sore), that is a different condition with its own treatment. [How To Treat Rodent Ulcers In Cats](/knowledge/veterinary-medicine/clinical-methods/how-to-treat-rodent-ulcers-in-cats) explains the difference.

## Limitations and When to Contact a Veterinarian

No article can tell you whether a specific sore is cancer. Only a veterinarian who examines your cat and reviews test results can do that. Individual cases need a veterinarian.

Use these timing rules:

- **Emergency now:** trouble breathing, heavy bleeding, inability to swallow, fast-growing facial swelling, collapse.
- **Same day:** not eating for more than 24 hours, constant drooling, severe pain, sudden foul breath.
- **Within a few days:** any sore that has not healed in 1 to 2 weeks, a new lump, weight loss, or a change in chewing.
- **Routine visit:** mild tartar, stable bad breath, or a cat that needs a dental cleaning.

When in doubt, call your vet's office and describe what you see. A phone call costs nothing and can save weeks of waiting.

## Frequently Asked Questions

### Can a mouth ulcer in a cat turn into cancer?

Chronic irritation and inflammation may raise the risk of oral cancer over time, but most ulcers do not become cancer [1]. The bigger concern is that a cancer can look exactly like an ulcer at first. That is why any sore that fails to heal within 1 to 2 weeks needs a veterinary exam and possibly a biopsy.

### Is cat mouth cancer painful?

Yes, oral tumors are often painful, especially once they invade bone or press on nerves [1]. Cats hide pain well, so you may only see subtle signs like dropping food, chewing on one side, or eating less. Pain control is an important part of care even when the tumor itself cannot be cured.

### How fast does oral cancer grow in cats?

Oral squamous cell carcinoma is locally invasive and aggressive, and many cats die of the disease within a few months of diagnosis [6]. Growth speed varies by tumor and by cat, so the only way to know your cat's situation is through a veterinary exam and staging tests.

### Are certain cats more likely to get mouth cancer?

Oral squamous cell carcinoma most often affects older, non-pedigree cats, and there is no clear sex or breed predisposition [1]. Age is the strongest pattern. That makes regular mouth checks especially important for senior cats.

### Can I catch mouth cancer from my cat?

No, you cannot catch cancer from your cat. Some mouth infections, such as calicivirus, can spread between cats, so keep a cat with active mouth ulcers away from other cats until your vet says it is safe [2]. Wash your hands after handling your cat's food bowls and toys.

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## Related Articles

- [Cat Bad Breath: When Is It a Sign of Illness?](/knowledge/veterinary-medicine/vet-visit-decisions/cat-bad-breath-when-to-worry)
- [Dental Disease In Dogs And Cats](/knowledge/veterinary-medicine/dental-care/dental-disease-in-dogs-and-cats)
- [How To Treat Rodent Ulcers In Cats](/knowledge/veterinary-medicine/clinical-methods/how-to-treat-rodent-ulcers-in-cats)
- [Prevent Dental Problems In Cats](/knowledge/veterinary-medicine/dental-care/prevent-dental-problems-in-cats)
- [Cat Coughing and Gagging: Causes and Urgency](/knowledge/veterinary-medicine/vet-visit-decisions/cat-coughing-and-gagging)
- [Cat Choking Causes](/knowledge/veterinary-medicine/clinical-methods/cat-choking-causes)
- [Mouth Cancer in Cats: Prognosis and When to Euthanize](/knowledge/veterinary-medicine/senior-and-chronic-care/mouth-cancer-cats-prognosis-euthanasia)
- [Cat Bump on the Lip or Mouth: Causes and Next Steps](/knowledge/veterinary-medicine/symptom-guides/cat-bump-on-lip-mouth)
- [Tumors on a Cat's Mouth, Jaw, or Tongue: What to Do](/knowledge/veterinary-medicine/dental-care/cat-mouth-jaw-tumor)

## References

1. [Feline oral squamous cell carcinoma: recent advances and future perspectives](https://pubmed.ncbi.nlm.nih.gov/41158948/). Frontiers in veterinary science, 2025.
2. [Disorders of the Mouth in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/disorders-of-the-mouth-in-cats). Merck Veterinary Manual.
3. [Genomic landscape and gene expression profiles of feline oral squamous cell carcinoma](https://pubmed.ncbi.nlm.nih.gov/37266381/). Frontiers in veterinary science, 2023.
4. [Solid type primary intraosseous squamous cell carcinoma in a long hair cat](https://pubmed.ncbi.nlm.nih.gov/41630734/). Open veterinary journal, 2025.
5. [Tracheal Squamous Cell Carcinoma in an Adult Cat](https://pubmed.ncbi.nlm.nih.gov/42433005/). Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association, 2026.
6. [Whole Exome Sequencing of Feline Oral Squamous Cell Carcinoma Reveals Genomic Parallels With Human Head and Neck Squamous Cell Carcinoma](https://pubmed.ncbi.nlm.nih.gov/41725028/). Veterinary and comparative oncology, 2026.
7. [Feline Oral Squamous Cell Carcinoma: A Critical Review of Etiologic Factors](https://pubmed.ncbi.nlm.nih.gov/36288171/). Veterinary sciences, 2022.
8. [First Description of Oral Microbiota in Domestic Cats Affected by Oral Squamous Cell Carcinoma](https://pubmed.ncbi.nlm.nih.gov/41754458/). Pathogens (Basel, Switzerland), 2026.

## Further Reading

- [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners)
- [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information)
- [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)