Stomatitis in Horses: Mouth Inflammation, Drooling, and Oral Pain

Stomatitis is inflammation of the tissues inside the mouth. In horses, that may involve the lips, gums, cheeks, tongue, palate, or other oral surfaces. The inflamed tissue can look red, swollen, ulcerated, or raw, and it often becomes painful enough to interfere with normal eating and drinking.

This is not one single disease. Instead, stomatitis is a clinical problem with many possible causes. A horse may develop it after mouth trauma from sharp plant material, after contact with irritating chemicals, or as part of an infectious disease process. Because the mouth is essential for chewing, swallowing, and bit acceptance, even mild inflammation can affect comfort and performance.

Many pet parents first notice frothy drool, quidding hay, bad breath, or resistance when the mouth is handled. Some horses also lose weight or drink less because swallowing hurts. While some cases are short-lived and improve once the irritant is removed, others need a more complete workup to rule out dental disease, foreign material, or reportable infections.

Your vet will focus on identifying the underlying cause, not only calming the inflammation. That matters because treatment options and biosecurity steps can look very different depending on whether the problem is trauma, toxin exposure, dental disease, or an infectious condition.

Stomatitis in horses has many possible causes. One of the most common is direct irritation or trauma inside the mouth. Sharp awns from barley, foxtail, spear grass, porcupine grass, or similar plants can lodge in oral tissues and create severe inflammation. Horses may also develop short-term stomatitis after contact with chemical irritants, including topical blistering products if they lick treated areas.

Feed and pasture exposures matter. Rough, stemmy forage, embedded foreign material, or plants associated with oral irritation can all contribute. In some horses, the mouth inflammation is secondary to another oral problem, such as dental abnormalities, sharp enamel points, wounds, or trapped debris that keeps rubbing the tissues.

Infectious disease is another important category. Vesicular stomatitis can cause painful oral lesions and drooling, and it is especially important because it is a reportable disease in the United States. During outbreaks, insect exposure plays a role in transmission risk, and affected horses may need movement restrictions and biosecurity precautions.

Less often, your vet may consider other differentials that can mimic or accompany stomatitis, including actinobacillosis, papillomas around the lips and mouth, toxin exposure, or systemic illness. That is why a careful oral exam and history are so important before deciding on treatment.

Diagnosis starts with a full history and physical exam. Your vet will ask about recent pasture changes, hay type, travel, insect exposure, new topical products, dental history, and whether any other horses are showing similar signs. Because horses with oral pain may resist handling, a complete mouth exam often requires sedation so the tissues can be inspected safely and thoroughly.

During the oral exam, your vet looks for ulcers, embedded plant material, wounds, dental abnormalities, foul odor, swelling, and areas of tissue damage. Sedation may allow removal of foreign material such as grass awns at the same visit. If the findings suggest a straightforward traumatic or irritant cause, treatment may focus on removing the trigger and supporting healing.

If lesions are more severe, blister-like, widespread, or suspicious for infection, your vet may recommend additional testing. That can include swabs, bloodwork, or samples submitted through approved laboratories if vesicular stomatitis is a concern. Because vesicular stomatitis can resemble other serious foreign animal diseases, your vet may advise isolation and limited movement until results are clear.

Some horses also need a dental evaluation, especially if they are dropping feed, resisting the bit, losing weight, or have chronic bad breath. The goal is to identify the cause driving the inflammation so care can be matched to the horse's needs and the farm's biosecurity situation.

Prevention starts with reducing oral irritation. Check hay and pasture quality, especially if your area has foxtail, barley awns, spear grass, or other sharp plant material that can lodge in the mouth. If a horse develops drooling or oral pain after a feed change, stop that forage and ask your vet whether the batch should be avoided.

Routine oral care also matters. Regular dental examinations help catch sharp points, abnormal wear, trapped feed, and other problems that can irritate the mouth or make chewing painful. The AAEP recommends at least annual dental exams for mature horses, and horses 2 to 5 years old often benefit from exams twice yearly because their mouths are changing quickly.

Use topical products carefully and follow label directions so horses cannot lick irritating substances from their legs or skin. If your horse is being treated with a product that could irritate the mouth, ask your vet about safe application and monitoring.

During vesicular stomatitis outbreaks, prevention also includes biosecurity and insect control. Your vet may recommend housing horses indoors or under cover during peak insect activity, using fans in stables, applying insect repellents, and limiting horse movement if suspicious oral lesions appear. Early isolation and prompt veterinary evaluation can help protect both your horse and the rest of the barn.