A raw-looking sore on your cat’s lip, a red, raised itchy patch on the belly, or a firm swelling on the chin can all belong to the same group of skin conditions: the eosinophilic granuloma complex (EGC). The name comes from eosinophils, a type of white blood cell that dominates the inflammation in these lesions. [3]
A clinical review in the Journal of Feline Medicine and Surgery calls EGC a common group of skin diseases in cats that vets recognize easily but still do not fully understand. [1] This guide explains the main forms, the usual triggers, and how vets approach treatment.
The three main forms
Veterinary reviews group three kinds of lesion in this complex: the indolent (eosinophilic) ulcer, the eosinophilic plaque and the eosinophilic granuloma. [3][5]
1. Eosinophilic ulcer (“rodent ulcer” or indolent ulcer)
- An ulcer at the lip or inside the mouth [3][4]
- One review suggests these mouth lesions may come from allergens that stay in contact with the lips and mouth, since cats groom so much [4]
2. Eosinophilic plaque
- A red, raised patch, usually on the belly and thighs [3]
- Plaques on the lower belly can join up into larger areas, and they are part of the itchy skin picture seen in allergic cats [2][5]
3. Eosinophilic granuloma
- Firm nodules or swellings, typically on the legs and chin [3]
- Granulomas can also form inside the mouth, including on the roof of the mouth [4][6]
A cat can have more than one form. The clinical review adds that lesions are often severe, can itch or hurt (sometimes a lot), and may keep coming back. [1]
What causes it?
In many cats EGC is an allergic (hypersensitivity) reaction; in others no cause is found. [3] The University of Minnesota dermatology handbook names these as the main allergies to rule out when a cat has EGC lesions: [2]
- Flea bite allergy
- Food allergy
- Environmental allergy (feline atopic skin syndrome), in which EGC lesions are one of four typical skin patterns [2][5]
The look of the lesion does not tell the vet which allergy is behind it, so each trigger has to be ruled in or out. [4] Because allergies are so often involved, see our guide to itchy cats and overgrooming, which covers flea, food and environmental allergy in more detail.
Which cats get it?
According to the clinical review, age and breed do not seem to matter. A few studies point to female cats being affected more often, but other studies have not confirmed this. [1]
How vets diagnose it
Recognizing the lesions is usually the easy part; working out what is driving them is harder. [1] Vets normally base the diagnosis on how the lesions look plus cytology (a sample from the surface) that shows many eosinophils. [6]
To find the trigger, the handbook describes: [2]
- Ruling out parasites with skin scrapings, tape samples and a trial of parasite control
- A strict food elimination trial with a home-cooked or prescription diet
- Allergy testing, used mainly to choose allergens for allergy shots rather than to make the diagnosis
A biopsy can help confirm the diagnosis, especially for mouth sores, because other problems such as oral tumors can look similar. [6] Bumps on the chin can also be chin acne; see cat chin acne.
How it is treated
Treatment depends on the cause your vet finds. For a cat with environmental allergy that can mean year-round flea and parasite control plus allergy shots or medicines that calm the immune response. [2] Your vet will choose the medicines, if any, for your cat.
What to expect over time: the review notes that some cats have one episode that clears with treatment, while others relapse and a few respond poorly to treatment. Many cats need management for life. [1]
When to see your vet
Book a visit if your cat has:
- A sore, ulcer or swelling on the lip, chin or mouth
- A red, raised or weeping patch anywhere on the skin
- Itching, overgrooming or hair loss
- Lumps on the paw pads, chin or thighs
- A sore that keeps coming back or is getting bigger
See your vet promptly if your cat has trouble eating, drools, or a lip sore is growing.
FAQ
What is a rodent ulcer in cats?
It is another name for an eosinophilic (indolent) ulcer, an ulcer that forms on the lip or in the mouth as part of this complex. [3][4]
Is eosinophilic granuloma complex cancer?
No. It is an inflammatory skin condition, often linked to allergy. [3] Some mouth tumors can look like it, though, so your vet may suggest a biopsy to be sure of the diagnosis. [6]
Will my cat need lifelong treatment?
Some cats have one episode that clears with treatment; others have flare-ups that come back. [1] Your vet will look for and treat any trigger, such as fleas or a food or environmental allergy. [2]
Is it contagious?
Reviews describe EGC as an allergic-type reaction or one with no known cause, not as an infection. [3] Ask your vet whether your cat’s case needs any precautions around other pets.
The bottom line
Eosinophilic granuloma complex covers lip ulcers, itchy raised plaques and firm nodules in cats. It is often linked to flea, food or environmental allergy, so your vet will look for the cause as well as treat the sores.
This article is for general information and is not a substitute for veterinary advice. If your cat has a sore, ulcer or lump, please see your veterinarian.
Sources
- Buckley L, Nuttall T. Feline eosinophilic granuloma complex(ities): some clinical clarification. J Feline Med Surg. 2012;14(7):471-81. PMID 22736681. https://pubmed.ncbi.nlm.nih.gov/22736681/
- Torres SMF. 2.2 Atopic Skin Syndrome, Feline. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/atopic-skin-syndrome-feline/
- Pițuru MT, Apetroaei-Leucă MM, Ștefan G, et al. Topical Anti-Inflammatory Therapies in Veterinary Medicine: Advancing Animal Health Through a One Health Approach. Animals. 2026;16(8):1252 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC13113859/
- Marsella R. Atopic Dermatitis in Domestic Animals: What Our Current Understanding Is and How This Applies to Clinical Practice. Vet Sci. 2021;8(7):124 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC8310319/
- Gedon NKY, Mueller RS. Atopic dermatitis in cats and dogs: a difficult disease for animals and owners. Clin Transl Allergy. 2018;8:41 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC6172809/
- Whybrow K, Hernon T, Pilot M. Menrath ulcers in cats: four cases (2014-2023). J Small Anim Pract. 2025;66(5):346-352 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12079305/