Eosinophilic granuloma complex (EGC) is a group of three skin reactions in cats — indolent ulcers, eosinophilic plaques, and linear granulomas — each driven by an overactive immune response, most often to allergens. The condition is not contagious, and most cats improve significantly with proper allergy management and short-term immunosuppression.
Last reviewed: June 2026
What Is Eosinophilic Granuloma Complex?
Eosinophilic granuloma complex refers to three distinct but related skin lesion types that share a common underlying mechanism: excessive eosinophil and mast cell activity triggered by an allergic reaction — most commonly to flea bites, environmental allergens such as dust mites or pollens, or food proteins. The three presentations are:
- Indolent (rodent) ulcer — a well-demarcated, raised, ulcerated lesion on the upper lip, usually painless despite its dramatic appearance
- Eosinophilic plaque — a raised, moist, intensely itchy lesion typically on the abdomen or inner thighs, often leading to self-trauma and hair loss
- Eosinophilic (linear) granuloma — a linear streak or firm plaque on the back of a hind leg or in the mouth, sometimes causing difficulty eating
As described in Côté's Clinical Veterinary Advisor, any of these lesions can appear alone or in combination, and individual cats may shift between lesion types over time.
What Signs Should You Look For?
Moriello, 2017, Vet Clinics of North America Small Animal Practice confirmed that EGC lesions are among the most common allergy-associated dermatological findings in cats presenting to primary care practices.
Key signs include:
- Upper lip swelling or ulcer — often mistaken for a bite wound or tumor
- Intense scratching or licking at the belly or inner thighs with resulting hair loss and raised, moist, red skin patches
- Firm, yellowish-pink linear streaks on the back of the hind leg — often found incidentally during grooming or vet exam
- Nodules in the mouth — cats may drool, paw at their face, or eat reluctantly if oral lesions are present
- General overgrooming and bilateral symmetrical hair loss on the abdomen or flanks
How Vets Diagnose and Treat EGC
Diagnosis is primarily clinical based on characteristic appearance and location. Cytology (impression smear showing eosinophils) confirms the diagnosis; skin biopsy is reserved for atypical or treatment-resistant cases. Identifying the underlying allergen requires assessment for flea infestation, a strict 8–12 week diet elimination trial, and environmental allergen testing.
Treatment has two goals: resolve the current lesion and eliminate the underlying trigger.
- Corticosteroids (prednisolone orally or methylprednisolone acetate injection) achieve rapid lesion resolution in 2–4 weeks
- Cyclosporine is an effective steroid-sparing alternative for cats requiring long-term immunosuppression, as described in Plumb's Veterinary Drug Handbook; Guaguere et al., 2004, JFMS documented cyclosporine efficacy in feline allergic and immune-mediated dermatoses
- Year-round flea prevention on all household pets is non-negotiable for flea-allergic cats — even one flea bite per week can perpetuate lesions
When to See a Vet
Call your vet today if:
- You notice a raised, red, or ulcerated lesion on your cat's upper lip
- Your cat is scratching or licking intensely at the belly or inner thighs with visible skin changes
- Your cat is drooling, pawing at its face, or reluctant to eat
- Lesions that previously resolved are returning more frequently
Go to the ER immediately if:
- Your cat cannot eat or drink due to painful oral lesions and has not eaten in more than 24 hours
- A lesion is bleeding heavily or expanding rapidly
- Your cat is in severe distress from self-trauma — open wounds carry significant infection risk
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Frequently Asked Questions
What does an eosinophilic granuloma look like on a cat? The three lesion types look quite different. The indolent ulcer is a well-defined, reddish-brown ulcer on the upper lip. Eosinophilic plaques are raised, moist, intensely red patches on the belly or inner thighs with surrounding hair loss and irritation. Linear granulomas are firm, yellowish-pink streaks on the back of the hind leg. Your vet can distinguish the types on exam and may take a cytology sample to confirm.
Is eosinophilic granuloma complex contagious? No — EGC is an allergic and immune-mediated condition, not an infectious disease. It cannot spread between cats or from cats to people. However, if the underlying trigger is flea infestation, the fleas can bite other pets and humans, so household-wide flea control benefits everyone.
What causes eosinophilic granuloma complex in cats? The most common cause is flea allergy dermatitis — even a single weekly flea bite can perpetuate lesions in hypersensitive cats. Food allergy (most commonly to chicken, beef, or fish) and environmental allergies account for most remaining cases. A small proportion are idiopathic, meaning no clear trigger is identified despite thorough evaluation.
How much does EGC treatment cost? An initial exam and cytology typically runs $100–200. A biopsy adds $200–350 if needed. A course of prednisolone costs $20–50. Allergy workup including diet trial supplies and allergen testing can add $300–600 total. Cyclosporine for cats needing long-term immunosuppression runs approximately $60–120 per month depending on dose.
Will it come back after treatment? Often yes, unless the underlying trigger is found and eliminated. Cats treated with steroids alone without addressing root-cause allergies typically relapse within weeks to months. Cats whose specific allergen trigger is controlled through flea prevention, diet change, or immunotherapy often achieve long-term remission with minimal or no ongoing medication.
Still Not Sure if Your Cat Needs a Vet?
When you're not sure if this is wait-and-see or call-tonight, Voyage AI Vet triages in under 2 minutes. Describe what you're seeing in chat, share photos of your cat's lip, belly, or leg lesions, or hop on a live video call if you want a second pair of eyes. Every answer comes with citations to the actual veterinary literature it's pulling from — so you see exactly where the guidance comes from, not just a chatbot's word.