What you see. The starting point for addressing any equine health related issue is your observation.


Sores or Blisters on Mouth, Lips, Tongue, or Gums


Sores inside the mouth develop when the lining membrane is damaged, exposing the underlying tissue. This can result from traumatic injury. Wounds or sores in the corners of the mouth or on the tongue can be caused by a poorly fitting or functioning bit or from trauma from excessive force applied to the bit.

Sores can also be caused by a variety of disease processes, including ingestion of toxins (from plants and other sources) that damage the lining cells. Some viral diseases, including EHV-1 and Vesicular Stomatitis (VS), can also cause oral ulcers. NSAID (bute) toxicity will sometimes cause oral ulcers.

A common cause of sores within the mouth is ulceration around seed heads from hay, which become embedded in the gums and cause ulcers to develop.

Summer Sores can occur around the corners of the mouth. More rarely, different skin conditions like Equine Sarcoid and Squamous Cell Carcinoma occur here, at the junction of the oral mucous membranes and the skin of the lips.

  • Code Red

    Call Your Vet Immediately, Even Outside Business Hours
    • If the results of the Whole Horse Exam (WHE) in the resting horse indicate fever (Temp >101F/38.3C) or heart rate greater than 48 BPM.
    • If the horse seems to be having difficulty eating, in addition to showing this sign.
  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.

your role


What To Do

Assess your horse's general health using the Whole Horse Exam (WHE), paying particular attention to attitude and appetite. Seek veterinary assistance immediately if this sign is accompanied by depression or inappetence. You may assess your horse's mouth (wear gloves), but keep in mind that this observation is classically associated with Vesicular Stomatitis, a contagious disease.

In geographic locations where Vesicular Stomatitis exists, isolate your horse from others until your vet rules out this condition as a diagnosis.

What Not To Do

Do not assume that this problem is not associated with infectious disease. if you have any doubt, isolate the horse and contact your vet.

your vet's role


Your vet will examine your horse's general health and mouth and, depending on their findings, recommend additional diagnostics or treatments.
Questions Your Vet Might Ask:
  • Does the horse's attitude and appetite seem normal?
  • Do you notice any other signs of a problem?
  • Has the horse received any oral medications in the past week?
  • What is the horse's age, sex, breed and history?
  • Has the feed or management changed recently?
  • What are the results of the Whole Horse Exam (WHE)?

Diagnoses Your Vet May Consider

The cause of the problem. These are conditions or ailments that are the cause of the observations you make.

Very Common
Less Common
more diagnoses

Author: Doug Thal DVM Dipl. ABVP