Most canker sores heal on their own within one to two weeks, but the right treatments can cut pain significantly and speed up that timeline. These small, shallow ulcers on the inside of your mouth aren’t contagious and aren’t related to cold sores or cancer. They’re just painful, and the goal is to manage that pain while helping the tissue close faster.
The spelling “cancer sore” is a common mix-up. The correct term is “canker sore,” known medically as an aphthous ulcer. Here’s what actually works to get rid of them.
How Long Canker Sores Last
There are two main types. Minor canker sores, the kind most people get, are usually 2 to 5 mm across and heal spontaneously in 4 to 14 days. Major canker sores are 1 to 3 cm in diameter, sit deeper in the tissue, and can last anywhere from 10 days to 6 weeks. Major sores sometimes leave scars; minor ones almost never do.
Both types follow the same basic pattern: a tingling or burning sensation for a day or two, then a visible round or oval sore with a white or yellowish center and a red border. Pain peaks in the first few days, then gradually fades as the sore shrinks.
Home Remedies That Help
A saltwater rinse is the simplest and most widely recommended home treatment. Mix 1 teaspoon of salt into 1 cup of warm water, swish for about 30 seconds, and spit. You can do this several times a day. The salt draws fluid out of the swollen tissue, which reduces inflammation and helps keep the area clean. It will sting briefly, but the discomfort passes quickly.
Hydrogen peroxide diluted to half strength (equal parts 3% hydrogen peroxide and water) can also be dabbed directly onto the sore with a cotton swab. This helps disinfect the surface and may promote healing. Baking soda paste, made by mixing a small amount of baking soda with a few drops of water, works similarly by neutralizing acids in the mouth that irritate the sore. Apply it directly, let it sit for a few minutes, then rinse.
Ice chips or cold water held against the sore can temporarily numb the pain. Honey applied directly to the ulcer has mild antibacterial properties and creates a protective coating over the exposed tissue. These remedies won’t dramatically shorten healing time, but they make the days more tolerable.
Over-the-Counter Pain Relief
Benzocaine gels (sold under brand names like Orajel and Anbesol) are the most effective OTC option for immediate pain relief. Apply the gel directly to the sore up to four times a day. The numbing effect kicks in within minutes and lasts long enough to eat or drink comfortably. Don’t use benzocaine products for more than two consecutive days without checking with a dentist or doctor, and keep them away from children under two.
OTC protective pastes create a barrier over the sore, shielding it from food, drinks, and your teeth. These are especially useful if the canker sore is in a spot that gets constantly irritated, like the inside of your lip or along your gum line. Some products combine a numbing agent with a protective coating, which handles both pain and mechanical irritation at once.
When You Need a Prescription
If you get canker sores frequently or they’re unusually large, a doctor or dentist can prescribe a steroid paste to apply directly to the ulcer. These work by suppressing the inflammatory response that causes the pain and swelling, which speeds healing noticeably. Prescription-strength options are typically applied four times daily, held directly against the sore.
For sores that keep recurring with no breaks between outbreaks, steroid injections directly into the lesion are sometimes used. This sounds more dramatic than it is. The injection delivers a concentrated dose of anti-inflammatory medication right where it’s needed, and relief is usually rapid.
Preventing Canker Sores From Coming Back
One of the most evidence-backed prevention strategies is surprisingly simple: switch to a toothpaste without sodium lauryl sulfate (SLS). SLS is the foaming agent in most toothpastes, and a systematic review of clinical trials found that people who switched to SLS-free toothpaste had significantly fewer ulcers, shorter outbreaks, fewer episodes overall, and less pain. Brands like Sensodyne, Biotene, and some versions of Tom’s of Maine are SLS-free. Check the ingredient list on the back.
Common triggers to watch for include acidic foods (citrus, tomatoes, pineapple), spicy foods, rough-textured snacks like chips or crusty bread, and accidental cheek bites. Stress is another well-documented trigger. If you notice a pattern between stressful periods and outbreaks, that connection is real, not imagined.
Nutritional Gaps That Fuel Recurrence
Deficiencies in iron, zinc, folate, and vitamin B12 are all linked to recurrent canker sores. Of these, B12 has the strongest clinical evidence for prevention. A review of multiple trials found that taking 1,000 micrograms of B12 daily (as a sublingual tablet that dissolves under the tongue) significantly reduced the number of outbreaks, the number of sores per outbreak, and how long each sore lasted. The benefits became most pronounced after about six months of consistent daily use. B12 supplements are inexpensive and widely available at any pharmacy.
If you get canker sores more than a few times a year, it’s worth asking your doctor to check your B12 and iron levels with a simple blood test. Correcting a deficiency can sometimes stop the cycle entirely.
Signs a Sore Needs Professional Evaluation
A mouth sore that lasts longer than two weeks is considered chronic and warrants a professional look. Most canker sores resolve well before that mark, so persistence is an important signal. Other reasons to get it checked: the sore is unusually large (bigger than a centimeter across), you’re getting new sores before old ones heal, you have a fever alongside the sore, or the pain is severe enough that you can’t eat or drink adequately.
Canker sores are not oral cancer, but oral cancer can sometimes look like a sore that won’t heal. Any single ulcer that persists beyond three weeks, especially if it’s painless and firm, should be evaluated by a dentist or oral surgeon to rule out something more serious.