Most mouth blisters heal on their own within one to two weeks, but the right care can speed recovery and cut down on pain in the meantime. The best approach depends on what type of blister you’re dealing with, because canker sores (inside the mouth) and cold sores (on or around the lips) have completely different causes and treatments.
Canker Sores vs. Cold Sores
Before you treat a mouth blister, figure out which kind you have. Canker sores are painful white or yellow ulcers with a red border that appear inside the mouth, on the inner cheeks, lips, or tongue. They’re not contagious and don’t have a single known cause, though stress, minor injuries (like biting your cheek), smoking, and deficiencies in iron, folate, or vitamin B12 can trigger them.
Cold sores look different. They’re clusters of small, fluid-filled blisters that form on the outside of the mouth, typically along the border of the lips. They’re caused by the herpes simplex virus (usually type 1) and are contagious, especially when the blisters are open and weeping. The tingling or burning sensation that shows up before the blisters appear is your signal that an outbreak is starting.
How to Treat Canker Sores
Minor canker sores, the most common type, usually heal within one to two weeks without any treatment. Larger ulcers can take several weeks. Your goal is to reduce pain, avoid irritating the sore, and give your mouth the best conditions to heal.
A saltwater or alkaline rinse is one of the simplest and most effective home treatments. St. Jude Children’s Research Hospital recommends mixing 1 teaspoon of table salt and 1 teaspoon of baking soda into 4 cups of warm water. Swish gently for 30 seconds and spit. This helps keep the area clean, reduces bacteria, and creates an environment that supports healing. You can repeat this several times a day, especially after meals.
Over-the-counter oral gels or patches that contain a numbing agent can take the edge off pain, particularly before eating. Look for products designed specifically for mouth sores at any pharmacy. For stubborn or especially painful ulcers, a dentist or doctor can prescribe a stronger topical treatment or a medicated mouth rinse.
How to Treat Cold Sores
Because cold sores are caused by a virus, they respond to antiviral medication. Prescription antiviral tablets work best when taken at the very first sign of an outbreak, during that initial tingling or itching stage. A typical course is just one day of treatment, with two doses taken about 12 hours apart. Starting early can shorten the outbreak and reduce its severity. If you get cold sores frequently, talk to your doctor about keeping a prescription on hand so you can start treatment immediately.
Over-the-counter antiviral creams are also available and can modestly reduce healing time, though they’re less effective than oral medication. Cold sores typically clear up in 7 to 10 days regardless of treatment, but antivirals can shave a day or two off that timeline and reduce pain.
Foods That Slow Healing
What you eat matters more than most people realize. Acidic foods and drinks lower the pH in your mouth, disrupting the protective layer over your oral tissue and leaving sores more exposed. The obvious offenders are citrus fruits, fizzy drinks, and alcohol. Less obvious triggers include strawberries and tomatoes, both of which are acidic enough to irritate existing ulcers or provoke new ones.
Spicy and very salty foods also irritate the delicate lining of the mouth. And if you already have a sore, pay attention to texture. Hard, crunchy, or sharp-edged foods like crusty bread, chips, or raw vegetables can physically scrape the ulcer and delay healing. Soft, cool, bland foods are your best bet until the sore closes up.
Preventing Repeat Outbreaks
If you get canker sores regularly, one of the easiest changes you can make is switching to a toothpaste free of sodium lauryl sulfate (SLS). SLS is the foaming agent in most toothpastes. It’s effective at cleaning, but it can irritate the mouth’s soft tissue. Some reports show that people who switched to SLS-free toothpaste experienced up to a 70% reduction in ulcer frequency. SLS-free options are widely available at most drugstores.
Nutritional deficiencies are another common driver of recurrent canker sores. Low levels of vitamin B12, folate, and iron are all linked to repeat outbreaks. If you’re getting canker sores frequently, especially more than a few times a year, it’s worth having your levels checked with a simple blood test. Correcting a deficiency through diet or supplements can dramatically reduce how often sores come back. Foods rich in B12 (meat, fish, dairy, fortified cereals), folate (leafy greens, legumes, fortified grains), and iron (red meat, beans, spinach) are worth prioritizing.
For cold sore prevention, common triggers include sun exposure, stress, illness, and fatigue. Using a lip balm with SPF, managing stress, and getting adequate sleep can all reduce the frequency of outbreaks. People with frequent cold sores (six or more per year) may benefit from daily suppressive antiviral therapy prescribed by a doctor.
When a Mouth Sore Needs Attention
Most mouth blisters are harmless, but some warrant a closer look. The key threshold is two weeks. Any mouth sore that hasn’t healed after two weeks, or that keeps coming back in the same spot, should be evaluated by a dentist or doctor. Lesions that are red and white, feel hard or fixed to deeper tissue, bleed easily, or grow rapidly raise concern for something more serious, including oral cancer. New or changing pigmented (dark-colored) spots in the mouth also deserve professional evaluation. These situations are uncommon, but catching them early makes a significant difference in outcomes.