Lip Sores & Mouth Ulcers In Cats

For a variety of reasons, lip and mouth problems are common in both kittens and cats. Most are easy to fix, but beware: they are hard to tell apart and some are extremely serious. Here are the essential facts for cat owners.

Causes Of Lip & Mouth Sores

In order of frequency, oral lesions of cats are most often caused by:

  • Eosinophilic granuloma complex
  • Viral infection
  • Renal failure
  • Gingivitis & stomatitis
  • Squamous cell carcinoma
  • Chemical or physical injury
  • Herpesvirus

Now let’s look at each of these in detail.

Eosinophilic Granuloma Complex

EGC is the name for a variety of diseases all caused by an accumulation of a particular white blood cell called eosinophil (“Ee-Oh-Sin-Oh-Fil”). These are the cells normally associated with allergies and parasites, but in EGC they cause ulcers, erosions, swellings or plaques of the skin and mouth.

The picture at the start shows a typical lip margin ulcer caused by EGC. If this early lesion is untreated it will spread to both sides and cause permanent erosion of the lips. I’ve deliberately chosen a mild case so you can identify it in time.

cat swollen chin
swollen chin caused by EGC

The picture here is another version of EGC where the chin of a cat gets puffy and swollen. If you look closely you can see the swollen area of gum has a yellowish tinge from the eosinophils.

Treatment with corticosteroids is usually simple, cheap and effective. There’s a link in some cats with flea bite so you should also add a good cat flea preventative whether you’ve seen fleas or not.

If there isn’t a quick response, I always double check the diagnosis with a biopsy or blood test to rule out the other conditions below.

Viral Infection

cat flu look
Mouth ulcers, conjunctivitis and nasal discharge in a poor kitty with cat flu

Both cat flu viruses commonly cause tongue ulcers especially in kittens. Sometimes they also cause gum ulcers, and are even linked with stomatitis (see later). Nasty!

You can read all about cat flu here.

Renal Failure

Uraemic ulcers cat

These odd white ulcers on the gums are associated with the uraemic syndrome of advanced kidney disease. Look closely and you’ll see another ulcer on the edge of the tongue. These have occurred due to high blood levels of toxins that are normally excreted by the kidneys.

Sadly, uraemia is a late and very bad sign usually associated with a poor response to treatment. Where possible, making a diagnosis earlier using routine wellness testing gives much better outcomes.

Gingivitis & Stomatitis

Without good dental care, all cats eventually develop gingivitis. However, in some unlucky ones, mouth inflammation and infection appears more rapidly. Causes include viral infections such as cat flu and FIV, genetic faults, and poor early nutrition.

cat stomatitis extractions
Improvement after tooth removal

Gingivitis in affected cats often progresses to stomatitis, as the inflammation and ulceration spreads away from the tooth-gum margin. These cats may continue to eat, but are usually in severe pain. Signs of gingivitis-stomatitis include bad breath, reluctance to eat hard food, drooling, and pain on opening the mouth.

If you get to look inside, you’ll see a horror show of bleeding and ulcerated gums. While they improve with good dental hygiene, severe cases of stomatitis respond best to complete tooth removal. It’s a radical step but it’s all-too-often necessary to treat the ongoing pain.

Squamous Cell Carcinoma

Although cancers are thankfully less common, they have a bad habit of masquerading as other conditions. This is especially true for squamous cell carcinoma (SCC), which can look either like a lump or like a slowly spreading ulcer or sore.

SCC is well known for affecting the noses and ears of cats that sunbathe. However, it can also be found inside the mouth, sometimes hidden by dental disease. This is why a biopsy is necessary whenever a supposedly simple condition doesn’t respond like it should.

Early diagnosis can lead to curative surgery, as well as a lot less unnecessary treatment.

Chemical or Physical Injury

Animals that groom are uniquely sensitive to their environment. When a cat gets toxic chemicals on the coat or feet, their first response is to lick them off. The most severe cases of oral ulceration I have seen have been a result of exposure to household cleaning fluids.

To prevent this, never allow cats near areas being bleached or disinfected, and remove any chemical exposure straight away using dilute dishwashing liquid.

Physical injury, such as foreign material becoming lodged in the mouth, is rare enough that I can’t recall a case. However, I’m sure there are some cats who’ll give anything a red hot go, so it’s always worth getting your vet to take a close look.


Lastly, I’m indebted to the comment below for the reminder about herpesvirus ulcerative dermatitis. It’s usually more severe and widespread (read one case here), but it can just affect the lip margins like described below.

In conclusion, if your cat has a mouth or lip sore, it’s probably one of the causes above. However, as much as I’ve tried to explain them, their appearances overlap too much to ever replace the opinion of an experienced vet. And with a diagnosis there’s a lot that can be done to help.

Have something to add? Comments are welcome below and will appear within 24 hours of lodging.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These help topics are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story! The information provided here is not intended to be used as a substitute for going to the vet. If your pet is unwell, please seek veterinary attention.


21 Replies to “Lip Sores & Mouth Ulcers In Cats”

  1. How long does it takevfor an idolent ulcer to clear. My cat was on pred 5mg for for 5 days then half a tablet for 5 days then half a tablet every other day until finished. It did not clear up so back to the vet for a further course of steroids and an antibiotic jab. We will look to a biopsy if that doesn’t clear it. Just wondered what is normal time frames. She is 11.5 and has just been diagnosed with hypothyroidism.

    1. Hi Katie. My impression is they should take about two or three weeks to clear up. It sounds like you’ve started out as best you can – good luck.

  2. Everything has been fine…appetite, activity…and then last night, while eating his wet food, Tommy growled and hissed at his food, and then he ran away. He later ate. Then this evening, while at the hard food bowl, he yelped, growled, hissed at his food, and then he ran away. I tried to look in his mouth, and he was obviously uncomfortable, and I think I saw a gray area on the outside of his mouth. Now, he is lying next to his wet food, ignoring in. I will call the vet tomorrow, but I am unsure when they will be able to see him. Any advice to tide me over?

    1. Hi Kristy. You will certainly still be able to find a vet. The most common cause for this is the gingivitis – stomatitis complex of cats.

    2. Hi , I am no vet & have no valid reason to be offering advice only simply that I’ve had cats my whole life , nurse fed runts of litters , stray cats etc …
      Your poor kitty !! My only thought was to perhaps try baby food , like turkey or chicken , it’s high quality & maybe easier to eat than cat food , while your cats mouth is healing .
      It may also help with nourishment , & if your cat can not eat enough to maintain health consider a liquid kitten formula for extra nutrition & to combat weight loss .
      I have no advice for the actual sore so sorry .
      Good luck !

  3. Hi:
    My cat was ok yesterday and today I noticed like an allergic reaction in her lips and surrounding area.
    I mixed a drop of liquid Benadryl with a drop of human oral benzocaine for tooth pain. I put a little on the area…. it seems to relieve her .
    We live on a tropical island (it’s like the movie “It’s a Bug’s Life ‘some seasons)and my theory is that maybe she was bitten by a small bug .
    Because of the pandemia,is difficult to find a veterinarian to take her.I have bactroban ointment,neosporin oint. But I don’t know what can I use because she licks the area.
    Please help me anyway you can.

    1. Hi Nora. I have seen allergic reactions on the lips and face of cats – they are usually very red and swollen all over. If that’s what’s happening, nothing really works well except an injection of a corticosteroid from the vet. Otherwise, you’re just hoping that it settles down by itself but the problem is often the cats will rub or scratch at it and make it worse very quickly. Most vets are still working through the pandemic so there should be one in most areas. Good luck.

  4. Hi, our 6 month old kitty has had two steroid shots now for indolent (rodent) ulcers which cause her upper front lips to swell forward. Now I see an ulcer between her teeth and cheek. Might this be a bacterial component that needs antibiotics? Should we be getting labwork done?

    1. Hi Anita. Although the diagnosis is probably correct, it is an unusually early age of onset. If it keeps coming back, I would be recommending a biopsy. I also often do find that antibiotics help the healing of the larger ulcers regardless of cause.

  5. My cat has a sore looks like an ulcer with a whitish spot in the middle and a reddish outline on her side upper lip. She had it for the past 2 weeks. She drools at times but she likes to drink plenty of water. Her appetite is fantastic and she often grooms and plays a lot too.
    Is there any home remedy that I can use to help to get rid of the ulcer or blister on her lip? Thank u.

    1. Hi Yan. The only thing that might possibly work is good flea control but the danger of waiting is that eosinophilic ulcers generally enlarge and can cause permanent disfigurement to the lips. To see a vet to have it cleared up shouldn’t be too expensive.

  6. I was really hoping you were close by so I could get a third opinion on the ulcer on my cats tongue. The vet said it’s cancer but I don’t think so. My cat has struggled with bad breath, drooling blood and now this huge ulcer. He acts completely normal and eats every meal. His xrays were negative for cancer in the lungs and his bloodwork was good. The ulcer opens and drains. So much blood comes out then it fills back up. I have him on lysine, prednisone, cosequin and amoxicillin. This has been going on for 2 months and he’s not a dying cat like the vet said. I took him for a second opinion and that vet said keep doing what you’re doing but the ulcer needs to go away. Someone told me her vet treats with stomach ulcer meds. Any suggestions. I’m at a loss 🙁

    1. Hi Brenda. All I can add is the value of getting a biopsy if not already done. Although this can be expensive, it’s the only way to get a definitive diagnosis. It may be the only option left.

  7. It is rare by sores on the chin or lips can also be caused by dermatological herpes. My cat continually got them and now I keepit under control with lysine fed daily.

    1. Hi Leslie. That is certainly true. In my experience, herpesviral dermatitis is usually a lot more severe than the sores pictured but obviously not in your case. Thank you.

  8. Thanks for the information on your site it has helped it looks like my cat might have an ulcer on the top side of her gum it looks very similar to the pictures. I will find out for sure today she is going to the vet for her mouth to be looked at.

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