What Is That on Your Lip?

April 2, 2026

Rodent Ulcers

Nancy Kerr

 

Have you ever noticed lesions around the upper lip on your cat? If so, they may have something called Feline indolent ulcers, also referred to as rodent ulcers or eosinophilic ulcers. These lesions are “sometimes referred to as ‘rodent ulcers’ because people once thought they were caused by rodent bites, although they are not”¹, or from the cat eating a rodent. “The term ‘indolent ulcer’ originates from the Latin term indolens, which means ‘without pain.’”²

Rodent ulcers are part of eosinophilic granuloma complex (EGC), which also includes the skin lesions eosinophilic plaques and eosinophilic granulomas. “The disease presents itself as a hard lesion that appears on the inside of a cat’s lip. While it looks painful, the ulcer seems to pose no discomfort to an infected cat. Feline eosinophilic granuloma complex affects a higher percentage of female cats than male cats. It is not breed-specific, with confirmed cases including mixed breeds and purebreds. Additionally, age doesn’t seem to make a difference.”³

Causes

There appears to be no clear answer as to why some cats get the ulcers and some don’t. However, there seems to be a link between the ulcers and allergens. “In 2005 the DVM Veterinary magazine released a report that cases of feline eosinophilic granuloma complex cases are linked to one of three causes: flea allergies, food allergies, and inhaled allergens.”³ Some research studies suggest that, in most cases, a form of allergic response (hypersensitivity reaction) may be involved, especially in cases that recur. Other studies suggest that the condition may at least be partially genetic or inherited.¹ What is known is that many cats heal when they’re removed from their usual environment. For an indoor/outdoor cat, moving the cat to being strictly indoors will solve the problem. For others, a dosage of antibiotics helps. Because antibiotics do work in some cases, there is also a belief that some rodent ulcers involve a bacterial infection.³

Symptoms

“The most common site for these lesions to appear is the lips, particularly the upper lip, where they appear as ulcers. The lesions vary in size from small and barely noticeable ulcers to large and extensive ulcers that disfigure the lips with bleeding occurring from some lesions.”¹ A swollen, puffy chin may be seen on some cats. They may also “develop in the mouth, especially along the gums and palate, or on other areas of the body. When lesions form in other locations, they usually appear as bald patches with raised areas of reddened skin rather than an ulcer. These lesions are often called eosinophilic plaques. Common sites are the hind legs and the stomach. The lesions can be large and may be itchy, as cats frequently lick and bite the affected areas.”¹

Diagnosing

A veterinarian will look at your cat’s medical history and physical examination findings and will generally make a preliminary diagnosis based on appearance of the lesion. In younger cats other possibilities should always be considered. Part of an initial allergy diagnosis will include flea control for all household pets as well as elimination of certain ingredients in a cat’s diet.

To obtain a definitive diagnosis, the veterinarian may perform a fine needle aspiration (FNA). “This involves taking a small needle with a syringe and suctioning a sample of cells directly from the lesion and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope. A similar test is also sometimes performed by pressing a microscope slide against a suspected eosinophilic plaque. By examining the imprint under the microscope, numerous eosinophils (a type of white blood cell) may be visible. In some cases, results from FNA may not be clear, and a biopsy may be necessary. A biopsy is the surgical removal of a piece of the lesion. The characteristic lip ulcers are highly suggestive of EGC, and a biopsy may not be required; however, if lesions are located elsewhere on the skin or in the mouth, a biopsy will rule out other diseases and conditions.”¹

It should be noted that the Bartonella infections can also form lesions on the lips and in the mouth. Your veterinarian should check to make sure the ulcers are not caused by this infection. If tests are positive, medications such as azithromycin are effective at killing the organism.³

Treatment

If an underlying cause has been identified treatment will focus on removing it. “Many cats with rodent ulcers are given anti-inflammatory medications, corticosteroids, and an antibiotic like penicillin or amoxicillin to help resolve lesions while the underlying disease is investigated. Often, these medications cure the ulcers and keep them from reoccurring for upwards of a year. Some veterinarians have had success treating rodent ulcers with essential fatty acid supplements.”³ If the secondary infection has not been dealt with lesions will tend to recur when the method of treatment is reduced or stopped.

Since insect bites can cause or worsen clinical signs or immune responses in affected cats, flea or pest control treatment is very important. “Some cats respond to elimination diet trials or hypoallergenic diets, suggesting an underlying food allergy is the cause. Most cats diagnosed with feline EGC benefit from a hypoallergenic food trial.”¹

The most common treatment is corticosteroids where “treatment may last for weeks or months because eosinophilic granulomas frequently recur and prolonged treatment minimizes the chance of recurrence.”¹ While side effects are usually minimal, prolonged use can cause increased weight and predisposition to diabetes mellitus. “Cyclosporine (Atopica) is another drug often used in cats to manage allergic skin disease. It acts as an immunosuppressant and is a good alternative for cats that cannot take steroids.”¹

“If the ulcers and additional allergic signs persist or recur despite an appropriate diagnosis, this suggests possible presence of environmental allergy (feline atopy). In atopic cats, intra-dermal allergy testing or serum allergy IgE testing should be conducted to identify offending allergens so that allergen-specific desensitization therapy may be pursued.”² “Long-term immuno-suppressive drug therapy is best avoided and replaced with thorough workup of underlying primary disease. Other methods of treatment reported to be occasionally successful include radiotherapy, cryosurgery, laser therapy, surgical excision, mixed bacterial vaccines, gold salt aurothioglucose, immunomodulating drugs such as oral or sub-cutaneous low dose interferon alfa, and oral essential fatty acid supplementation.”²

Prognosis

The prognosis for resolving a rodent ulcer is excellent if the underlying disease is identified and managed successfully. However, if the underlying disease is not controlled, recurrence of the lesion is likely. “Cats with recurring lesions for which no underlying cause can be found usually require long-term drug therapy to keep lesions in remission. These cats have a poorer prognosis as they may become refractory to or may develop unacceptable adverse effects as the result of medical therapy.”² Cats that are severely affected will require more aggressive treatment and referral to veterinary dermatologist may be required.

As the ulcers cause the cat no pain, both you and your veterinarian can work on pinpointing the allergen and removing them from the cat’s diet or surroundings. Unfortunately, cats may excessively lick the ulcer, which will cause more inflammation than the ulcer itself. Removal of any fleas from inside and outside the home and treatment of the cat with a topical flea repellent on a regular basis are also helpful. An air filtration system/purifier placed in rooms where your cat tends to spend the most time will help with any dust or pollen allergens in your home. Consider switching foods in order to make sure common allergens of corn, soy, and wheat products are avoided, and choose pure protein sources over byproducts.

Sources:

1. Courtney Barnes, BSc, DVM; Malcolm Weir, DVM, MSc, MPH; Tammy Hunter, DVM; Ernest Ward, DVM, Eosinophilic Granuloma Complex in Cats, 2025, Accessed 02/10/2026, https://vcahospitals.com/know-your-pet/feline-eosinophilic-granuloma-complex-in-cats

 

2. Jangi Bajwa, Feline indolent ulcers and their significance, Accessed 02/10/2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC6697023/

 

3. Feline Eosinophilic Granuloma Complex: Rodent Ulcer in Cats, Accessed 02/10/2026, https://www.vetinfo.com/feline-eosinophilic-granuloma-complex-rodent-ulcer-cats.html