CONDITION
Eosinophilic Granuloma Complex in Cats
Eosinophilic granuloma complex is a group of skin and mouth conditions in cats that share a common underlying pattern: clusters of immune cells called eosinophils gather in affected tissue, creating characteristic lesions. The name describes what is seen under the microscope rather than a single disease, and the exact trigger often remains unclear even after investigation. Owners typically notice one of several distinct patterns: ulcers on the upper lip, raised plaques on the belly or inner thighs, or thickened areas in the mouth. Some cats show little discomfort, while others may lick or scratch persistently. The appearance can be striking, and it is common to wonder whether the lesion is infectious, cancerous, or self-inflicted. This page explores what these patterns can look like when they first appear, what is understood about the immune processes underneath, how the condition is investigated and distinguished from other causes, and the range of approaches used to manage it. The course varies widely between individuals, and response to treatment can help clarify what is driving the reaction in a particular cat.
Why this matters now
Eosinophilic granuloma complex can appear at any age, but lesions often develop in young to middle-aged cats, typically between two and six years old. No single breed is uniquely affected, though some lines may show a slightly higher tendency. Environmental allergens, food proteins, and insect bites have all been associated with the condition in different individuals, but in many cases no clear trigger is identified even after careful investigation.
Lesions may appear suddenly or develop gradually over weeks. Some cats present with a single lesion that remains stable for months, while others develop new lesions in different locations or see existing ones expand and merge. Periods of apparent improvement can be followed by recurrence, and the pattern in one cat does not reliably predict the course in another. The extent and speed of change can vary widely, even within the same household.
Signals & patterns
Early signals
Swelling or ulcer on the upper lip
A thickened, often asymmetrical swelling develops on one or both sides of the upper lip, sometimes progressing to a raw, crater-like ulcer. The area may appear shiny or have a raised edge, and some cats show no sign of discomfort despite the prominent appearance.
Raised, pink plaques on the skin
Flat-topped, slightly raised patches appear on the belly, inner thighs, or neck, often hairless and with a moist, glistening surface. These plaques may be single or multiple, and some cats lick at them persistently whilst others seem unbothered.
Increased grooming of a specific area
The cat repeatedly licks or nibbles at the same patch of skin, sometimes creating a bald area before any visible lesion appears. The behaviour may be subtle at first, noticed only when the coat begins to thin or the skin looks slightly irritated.
Linear swelling on the back of the thigh
A firm, cord-like ridge develops along the back of one or both hind legs, running from the thigh towards the hock. The swelling is often symmetrical and may feel warm to the touch, though the overlying skin can appear normal or slightly pink.
Later signals
Thickened or ulcerated areas in the mouth
The roof of the mouth, tongue, or back of the throat develops raised, sometimes raw-looking patches that may interfere with eating or grooming. Drooling or a change in the way the cat picks up food can accompany these lesions.
Spreading or merging lesions
What began as a single plaque or ulcer expands in size or new lesions appear in different locations, sometimes joining together to form larger affected areas. The skin may become more visibly inflamed, and self-trauma from licking can complicate the picture.
Persistent hair loss and skin darkening
Repeated cycles of inflammation and healing can leave the skin thickened, darkly pigmented, and resistant to hair regrowth. The texture may feel leathery, and the underlying pattern of the original lesion can become harder to distinguish.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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