Also known as "indolent ulcer", rodent ulcers are ulcerations and swelling of the lip which develop in response to an underlying allergy. Rodent ulcer is part of a "syndrome" known as eosinophilic granuloma complex, which comes in three forms.
Eosinohiliic plaque, linear granuloma and rodent ulcer. This article will focus on rodent ulcers only.
White cells known as eosinophils have many roles, one of which is help to fight infections (viral infected cells, bacteria, fungi, parasites) by going to the site and releasing cytotoxic granules (this is known as degranulation), destroying the target. Rodent ulcers occur when eosinophils release their granules into local tissues, causing lesions. The exact cause of this isn't entirely known, but it is believed that common allergens such as flea bites, food and inhaled allergies trigger this.
Other suggested causes include dental infection and exposure to the feline leukemia virus, although not all cats who have rodent ulcers will have had exposure to the virus.
Cats of any age can develop rodent ulcers, they may appear once only or can recur. Despite the name, they have no connection to rodents.