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Why does my cat have a lip sore? Is it a rodent ulcer or allergy?

Updated on September 23rd, 2025

Pet's info: Cat | Domestic Mediumhair | Male | neutered | 11 years and 7 months old

My cat has what looks like some kind of sore on his upper lip. I am concerned about what it could be. Would you be able to tell from the attached pictures?

5 Answers

Most Helpful Answer

Answered By Lauren Kennedy, DVM

Veterinarian

Published on August 24th, 2017

This appears to be what is commonly referred to as a 'rodent ulcer'. The most common cause for these to pop up in cats is an allergy, typically to something in the food.
Sometimes these will resolve in their own, however sometimes they can become infected, long lasting, and problematic. If they become very large and painful it can discourage the cat from wanting to eat.

If this ulcer has been present for more than 2 weeks it is probably not going to go away on its own. At that time I would recommend taking you cat to the vet for treatment. Nathaniel may need antibiotics and an immunsuppresive drug like steroids or Atopica.

If the lesions keep coming back he may need to be on an immunosuppressive long term and/or a hypoallergenic diet.

I hope this helps. Thanks for using Petco Pet Education Center, formerly Petcoach. Best of luck.

3Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By David Elbeze, DVM, MRCVS
Veterinarian
Published on October 1st, 2018
It looks like a condition also known as "rodent ulcer", it's an autoimmune condition that is also linked to allergies, you will need to take him to the vet in order to get treated for that with steroids.
1Pet Parents found this answer helpful
Answered By David Elbeze, DVM, MRCVS
Veterinarian
Published on June 14th, 2018
IT looks like a condition also known as "Rodent Ulcer", it's an autoimmune condition, at the moment it looks very mild and it is probably not causing your cat any discomfort but it might get worse in the future and might require treatment if it does.
1Pet Parents found this answer helpful
Answered By Jeffrey Milner
Veterinarian
Published on August 2nd, 2017
That looks like something called a rodent ulcer to me. These generally require treatment with antibiotics and steroids to get rid of the problem. You should seek out some veterinary care to obtain these drugs. Hope this helps.
2Pet Parents found this answer helpful
Answered By Emily Luisana DVM
Veterinarian
Published on August 9th, 2017
This could be a few different things, but eosinophilic plaques/rodent ulcers, injuries, or infections would be high on my list. I think it is a good idea that you are going to the vet as some medications and a diet change could bring him relief! The good thing is most of these differentials are very treatable! I hope this helps!
1Pet Parents found this answer helpful

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