Eosinophilic Granulomas (Rodent Ulcers) in Cats

Eosinophilic Granulomas (Rodent Ulcers) in Cats

Animals Affected



Eosinophilic granulomas are ulcers or sores that develop on the lips and in the mouth of cats.  They occur when the cat’s immune system misdirects its activities and attacks the cat’s mouth.

The syndrome is painful.   Severe eosinophilic granulomas can become infected or can be disfiguring.

With treatment, most eosinophilic granulomas can be managed.  However, cats often develop many ulcers over their lives, and the syndrome can be a chronic problem.

The sores that develop in the syndrome were originally called rodent ulcers because veterinarians believed that they developed as a result of prey animals traumatizing the lips.  However, rodents have nothing to do with the syndrome.   Despite this, many people still refer to eosinophilic granulomas as rodent ulcers.

Eosinophilic granulomas are also known as eosinophilic granuloma complex.   Although the mouth is the most common site for the development of eosinophilic granulomas, they sometimes occur in other locations.


  • Eosinophilic granulomas usually occur as ulcers, sores, or blisters on the lips of the mouth.  The central or rear portions of the upper lip are most frequently affected. The sores may be covered with scabs, or they bleed or emit an unpleasant odor.
  • Rarely, sores may develop elsewhere on the body.
  • Signs of pain may occur in cats that suffer from eosinophilic granulomas.  Hiding, aggression, and other behavior changes may occur.
  • Cats with eosinophilic granulomas may exhibit decreased appetite due to pain associated with eating.

Risk Factors and Prevention

  • Individual susceptibility to eosinophilic granulomas appears to be hereditary or genetic.
  • Young and middle-aged cats (less than seven years old) suffer higher rates of eosinophilic granulomas than older cats.
  • Flea saliva and other compounds that stimulate the immune system may play a role in the development of eosinophilic granulomas.


  • Chronic pain is the most common complication.
  • Facial disfigurement may occur in cats that suffer from severe eosinophilic granulomas.
  • Behavior changes may lead to a weakened bond between the cat and its owner.
  • Weight loss and deterioration of body condition may occur if the syndrome interferes with food consumption.
  • Because eosinophilic granulomas often recur, owner frustration is common.


Diagnosis usually is made by visual assessment of the affected area.  Veterinarians occasionally biopsy or sample the affected site to confirm the diagnosis.


Eosinophilic granulomas often resolve when treated with prednisone or related medications.  These medications attenuate the function of the immune system.  Many cats require long-term therapy.

In rare instances, surgery may be used to clean and treat eosinophilic granulomas.

Appropriate flea control should be implemented.  Omega-3 oils (fish oil) may help prevent and heal eosinophilic granulomas.

Antibiotics such as clindamycin or Clavamox® may be prescribed for infected eosinophilic granulomas.


Many cats develop multiple eosinophilic granulomas over their lives. These cats may require chronic or repeated courses of treatment.

Although eosinophilic granulomas can occur repeatedly, some cats outgrow the syndrome as they mature.


Some experts believe that eosinophilic granulomas are related to inflammatory bowel disease, or IBD.   Eosinophilic granulomas occur when the immune system attacks the lips and mouth.  IBD occurs when the immune system attacks the stomach and intestines.

Rodent ulcer is a type of tumor in human beings.  Rodent ulcers in humans are not related to eosinophilic granulomas or rodent ulcers in cats.

Copyright © Eric Barchas, DVM. All rights reserved.
The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.