What Is Eosinophilic Granuloma Complex?
Eosinophilic granuloma complex (EGC) is a group of inflammatory lesions that show up on a cat’s skin, lips, or mouth. The name comes from eosinophils, a type of white blood cell that floods the tissue and creates raised sores or plaques. EGC is not a single disease. It is a reaction pattern, most often driven by flea allergy, other insect bites, food allergy, or environmental allergy, and sometimes by an underlying genetic tendency.
Vets usually describe three classic forms: indolent (rodent) ulcers on the upper lip, eosinophilic plaques on the belly or inner thighs, and linear or nodular eosinophilic granulomas on the back legs, chin, or in the mouth. A cat may have one form or several at once. EGC is different from ordinary atopic dermatitis, which is mainly itchy skin without these signature eosinophil-rich lesions, though the two can overlap when allergy is the root cause.
Why it matters
Lip ulcers and belly plaques are often blamed on fighting or simple infection. Treating only the sore without finding the allergy or flea trigger is why many cases keep coming back.
Signs Owners Notice
- A shiny, raw, or yellow-pink sore on the upper lip that may look like a rodent bite (indolent ulcer)
- Raised, moist, intensely itchy patches on the belly, groin, or inner thighs (eosinophilic plaques)
- Firm linear ridges or lumps on the back of the thighs, chin, or paw pads
- Drooling, pawing at the mouth, or difficulty eating if lesions are in the mouth
- Excessive grooming, hair loss, and secondary skin infection
Diagnosis
Your vet will examine the lesions and often take a cytology sample or biopsy to confirm eosinophils and rule out cancer, infection, or autoimmune disease. Allergy workup is the next step: strict year-round flea control, a veterinary prescription food trial for suspected food allergy, and sometimes allergy testing for environmental triggers. Bloodwork may show a high eosinophil count but is not required for diagnosis.
EGC should not be confused with a simple wound, a rodent bite, or ringworm. Mouth lesions also need to be distinguished from stomatitis and dental disease. Related allergy pages such as cat allergy medicine and dog food allergies cover overlapping triggers that also affect cats.
Treatment and Outlook
- Trigger control: year-round flea prevention for every pet in the home is the single most important step for many cats.
- Anti-inflammatory medicines: corticosteroids are commonly used short term to shrink lesions; some cats need longer or repeated courses.
- Allergy management: prescription diets, antihistamines in selected cases, cyclosporine, or allergen immunotherapy when environmental allergy is confirmed.
- Secondary infection: antibiotics or antifungals if bacteria or yeast are present on the skin.
- Surgery or laser: rarely needed and usually only for stubborn single lesions after medical control.
Most cats improve once the trigger is controlled and inflammation is reduced. Relapse is common if fleas return or the food trial is abandoned. Long-term outlook is good with consistent allergy and parasite control, though some cats need intermittent medicine for life.
Practical Tips for US Pet Owners
- Treat every cat and dog in the household for fleas year-round; see flea treatment for cats.
- Do not stop a prescription diet early — food trials usually need 8 to 12 weeks.
- Photograph lesions weekly so your vet can track response.
- Find a nearby practice through veterinary clinic listings.
When to see a vet
Book a visit for any lip ulcer, belly plaque, or mouth sore that lasts more than a few days, or if your cat stops eating because of oral pain.
Key Takeaways
- EGC is an allergy-linked reaction pattern in cats, not a contagious infection.
- The three forms are indolent ulcers, eosinophilic plaques, and eosinophilic granulomas.
- Flea control and finding the allergy trigger matter as much as steroids.
FAQ
Is eosinophilic granuloma complex contagious to people or other pets?
No. The lesions are not contagious. Fleas that help trigger them can move between pets, so treat the whole household.
Will the lip ulcer heal on its own?
Mild ulcers sometimes improve with flea control alone, but many need veterinary anti-inflammatory treatment and a trigger workup.
Is EGC the same as a rodent ulcer?
Rodent ulcer is the old name for the indolent lip form of EGC. It is not caused by rodents.