What causes a blister on the tongue?

A true blister is a raised bubble filled with clear fluid, sometimes tinged with blood. On the tongue, blisters break quickly because the surface is thin and constantly moving, so by the time you look in the mirror you may see a raw sore instead.

A lot of things people call a tongue blister are actually something else: a canker sore (a flat ulcer with a white or yellow base), or a lie bump (a solid, swollen papilla). Neither contains fluid. Knowing which one you have changes what helps.

• A burn. Cleveland Clinic classifies tongue burns like skin burns. A partial-thickness (second-degree) burn damages the layer under the surface and can blister. It typically takes one to two weeks to heal. Microwaved food, which heats unevenly, is a common culprit.
• A mucus cyst (mucocele). A soft, clear or bluish bubble that forms when a tiny saliva gland is damaged, often by a bite. Cleveland Clinic calls these harmless blisters; the underside of the tongue is a common spot. They are usually painless and often burst and heal, though they can return.
• Herpes simplex. A first herpes infection, most often in young children, can cause many small blisters across the gums, tongue and mouth with fever, sore throat and swollen glands. MedlinePlus notes symptoms can last up to 3 weeks. Later outbreaks usually appear on the lips as cold sores rather than on the tongue.
• Hand, foot and mouth disease. The NHS describes painful mouth ulcers following a sore throat and fever, with spots and blisters on the hands and feet. It is common in children but adults can get it too, and it usually clears in 7 to 10 days.
• Friction or a bite. Biting your tongue hard, or a sharp tooth, can raise a small fluid or blood blister that heals within days.

• Allergic or chemical reactions. Strong flavorings such as cinnamon, and some toothpastes or mouthwashes, can irritate the lining of the mouth and tongue. Cleveland Clinic cites a case of a tongue reaction after a cinnamon and chili hard candy. A reaction that keeps recurring with the same product is worth raising with a dentist.
• Autoimmune blistering diseases. Conditions such as pemphigus vulgaris and mucous membrane pemphigoid cause repeated blisters and raw areas in the mouth. The AAFP lists them among the causes of tongue inflammation. They need a specialist and a biopsy.
• Erythema multiforme or Stevens-Johnson syndrome. Severe reactions, often to a medicine or infection, that cause widespread mouth blisters along with skin lesions or sore eyes. Stevens-Johnson syndrome is a medical emergency.

• Do not pop it. Cleveland Clinic and MedlinePlus both advise against opening a mucus cyst yourself because of the risk of infection and tissue damage. The same goes for burn blisters: the roof protects the raw layer underneath.
• Cool it. Sip cold water, suck ice chips or a popsicle. Cleveland Clinic also suggests milk or a little honey to soothe a burn.
• Rinse gently with salt water to keep the area clean.
• Avoid hot drinks, spicy, salty and acidic food, and crunchy snacks until it heals.
• If it might be herpes, the NHS advises against kissing and oral sex until sores fully heal, and washing your hands after touching them. Do not share cups or utensils.
• Leave the scraper off the blister. Scraping would tear it open. Clean the rest of your tongue gently or take a few days off.
• Keep fluids up, especially in children with painful mouths, who may refuse to drink.

Most tongue blisters need no treatment beyond time. A doctor may prescribe antiviral medicine for herpes, which MedlinePlus notes works best when started early. Mucus cysts that keep returning can be removed by a dentist or oral surgeon. Severe burns, especially from very hot or caustic liquids that may also have been swallowed, need urgent care. Repeated or unexplained blisters are usually investigated with a biopsy.