What Are Causes of Blisters in the Mouth?

Mouth blisters are sores on the lips, cheeks, tongue, or areas inside or around the mouth. They can be caused by dental work, an accidental bite from eating, irritation or injury, viral infections, or cancer of the mouth.

A mouth blister is a sore on the lips, cheeks, tongue, or other soft areas inside or around the mouth. Everything from dental work to an accidental bite while eating can cause these uncomfortable blisters.

Many types of mouth sores will go away on their own, but some may require medical attention.

Mouth blisters can look different depending on their cause and where they appear. Generally, they appear as white- or yellow-capped sores or rashes anywhere on the surface of your lips, the insides of your cheeks, the tongue, or the gums. It can be painful to eat, drink, speak, or swallow while you have a mouth blister. 

The following are different types of mouth blisters: 

Canker sores 

Canker sores, also known as mouth ulcers, usually appear inside the lips, but they can also appear on the tongue, cheeks, and gums. They are usually under a half-inch long, are white or yellowish, and are oval-shaped, often with a red ring around them and slightly raised. Left alone, minor canker sores usually heal within a week. 
 

Cold sores

Cold sores, also known as oral herpes, appear outside of the mouth on the surface of the lips or the skin surrounding them. Caused by a virus, they are usually small with a white or yellowish surface and can form in patches of several at once. They begin with a tingling, burning, or itching sensation for a day or two, then grow into blisters.

Symptoms such as muscle aches, fatigue, headache, and fever can accompany a cold sore’s first appearance. Once the blisters pop, they scab over and heal without scarring in two to three weeks, but they can reappear later. Cold sores are highly contagious.

Transient lingual papillitis 

Also known as tongue or “lie” bumps, these are small, inflamed sores on the top or sides of the tongue. Usually very small, these blisters can have a red or white surface and occur when taste buds (papillae) become irritated. They can be painful, but they heal on their own within a few days after appearing.

Oral candidiasis

Sometimes referred to as thrush, this type of mouth blister is a white or light-colored rash that appears in patches on the tongue or other areas inside the mouth. This infection can cause burning sensations or soreness in the mouth or throat, along with bad breath. Thrush can sometimes heal on its own but may need medical treatment.

Blisters in the mouth can have a variety of causes:

Irritation/injury 

External irritation or injuries commonly cause canker sores and other mouth blisters. Accidentally biting your lips, as well as allergies, dental work, and certain toothpastes and mouthwashes, can lead to canker sores.

Viruses and infections 

A common cause of cold sores and other blisters outside and inside of the mouth is the herpes simplex virus. This infection can spread through kissing, oral sex, or sharing eating utensils and other objects that touch the mouth. Herpes usually isn’t serious, but it can cause complications for people with weakened immune systems from medication or pre-existing illnesses. 

Infections and viruses can also lead to thrush. The fungus that causes thrush, Candida, naturally lives in our mouths in small amounts. Our immune system is meant to keep this fungus under control. However, in older adults, very young children, and others with reduced immunity, the fungus can overrun the mouth and create a thrush rash.

Mouth cancer 

Early symptoms of mouth cancer include sores and other unusual marks or rashes inside the mouth. A sign of mouth cancer is bright red, white, or grey patches on the cheeks, under the tongue, and behind the back teeth. Generally, cancerous sores last beyond two weeks, unlike most canker sores and other mouth blisters.

If your mouth blisters do not resolve on their own within a few weeks or recur even with over-the-counter treatments, contact your doctor. The blisters could be a symptom of an underlying condition that needs attention.

Canker sores and other mild blisters in the mouth don’t require a medical test or diagnosis for over-the-counter treatment. If you’re concerned that they may stem from a larger issue, a doctor can perform tests to diagnose any underlying cause of the blisters, including a blood test or a biopsy.

Leave the mouth blister alone. Don’t bite, pick, or otherwise irritate it — this can lead to infections and/or permanent scarring. Holding ice to a canker sore can reduce swelling. 

Over-the-counter treatments can also speed healing and reduce pain. Home care can include careful teeth cleaning and/or baking soda washes. 

At the drugstore, look for products containing the active ingredient benzocaine, which is a topical anesthetic. If you’re unsure of what products to use, or if what you’re using has not been effective, contact your doctor.