Most canker sores heal on their own within about two weeks, but the right treatments can cut pain significantly and may speed up that timeline. The key is starting early: the sooner you treat a canker sore, the less miserable those days will be.
Canker sores are small, round ulcers that form inside the mouth, on the tongue, inner cheeks, or soft palate. They’re white or yellow with a red border, and they’re not the same thing as cold sores, which appear outside the mouth as clusters of fluid-filled blisters. Canker sores aren’t contagious. They’re driven by your own immune system overreacting to some trigger, whether that’s stress, a mouth injury, a food sensitivity, or a nutritional gap.
Salt Water and Baking Soda Rinses
The simplest and cheapest remedy is a salt water rinse. Mix one teaspoon of salt into a cup of warm water, swish it around your mouth for 30 seconds or so, focusing on the sore, then spit it out. Repeat a few times a day. The salt draws fluid from the inflamed tissue, which reduces swelling, and creates a less hospitable environment for bacteria. It will sting for a moment, but pain typically eases afterward.
Baking soda works similarly. Dissolve half to one teaspoon in four ounces of water and use it as a rinse, or mix a small amount with water to form a paste and dab it directly on the sore. Baking soda neutralizes acids in the mouth that can irritate the ulcer and helps clean the wound surface.
Over-the-Counter Gels and Rinses
Pharmacy shelves offer several categories of canker sore products, and understanding what each one does helps you pick the right one for your situation.
- Numbing gels (anesthetics): Products containing benzocaine (typically 5 to 20% concentration) temporarily deaden the nerve endings around the sore. These are your best option when eating or drinking is painful. Apply directly to the sore before meals.
- Protective pastes (occlusives): These form a physical coating over the ulcer, shielding it from food, temperature changes, and friction. They don’t contain active medication but can make a big difference in comfort, especially if the sore is in a spot that rubs against your teeth.
- Antiseptic rinses: Hydrogen peroxide (diluted to half strength with water) or other oxygen-releasing rinses help clean the ulcer surface. The foaming action loosens debris from the wound.
- Chemical cautery products: OTC products like Debacterol chemically cauterize the sore, destroying the damaged tissue on the surface. This approach may reduce healing time to about a week. Silver nitrate, another cautery option, hasn’t been shown to speed healing but can relieve pain.
For most people, combining a numbing gel with regular salt water rinses covers both pain relief and wound care.
Avoid Irritating the Sore Further
What you stop doing matters as much as what you start doing. Acidic foods like citrus, tomatoes, and vinegar-based dressings will aggravate the ulcer. So will salty chips, spicy food, and very hot drinks. Stick to soft, bland, cool foods while the sore is at its worst, usually the first three to five days.
Your toothpaste may also be part of the problem. Many toothpastes contain sodium lauryl sulfate (SLS), a foaming agent that can irritate the lining of the mouth. In a clinical trial, 90 participants who switched to SLS-free toothpaste reported that their canker sores didn’t last as long and caused less pain compared to periods when they used SLS-containing toothpaste. If you get canker sores regularly, switching to an SLS-free formula is one of the simplest preventive steps you can take. Brands like Sensodyne, Biotene, and some versions of Tom’s of Maine skip SLS.
Nutritional Deficiencies That Fuel Recurrent Sores
A single canker sore now and then is normal. But if you keep getting them, a nutritional gap could be the underlying cause. The deficiencies most closely linked to recurrent canker sores are vitamin B12, folate (vitamin B9), iron, and zinc. All four play roles in immune function, cell repair, or wound healing.
You don’t necessarily need supplements. B12 is found in meat, fish, eggs, and dairy. Folate is abundant in leafy greens, beans, and fortified grains. Iron comes from red meat, lentils, and spinach. Zinc is in shellfish, seeds, and nuts. If you suspect a deficiency, especially if you follow a restrictive diet, a simple blood test can confirm it and guide whether supplementation makes sense.
When a Canker Sore Needs Professional Treatment
Minor canker sores, the most common type, are smaller than a centimeter across (roughly pea-sized) and heal within two weeks without scarring. These rarely need anything beyond home care and OTC products.
Major canker sores are larger than one centimeter, intensely painful, and can take months to heal. They often leave scars. Herpetiform canker sores are a rarer type that appear as clusters of tiny pinpoint ulcers, sometimes fusing together into larger, irregular sores that make eating and speaking very difficult. These can persist anywhere from 10 days to over three months.
For severe or persistent sores, a dentist or doctor can prescribe a steroid mouth rinse. These are typically swished in the mouth for about five minutes and then spit out, used three times a day, to reduce the immune-driven inflammation that keeps the ulcer from closing. In-office options include laser therapy or electrocauterization, which can reduce pain and accelerate healing in a single visit.
What Actually Causes Canker Sores
The exact cause isn’t fully understood, and canker sores likely represent several different conditions rather than one single disorder. What’s clear is that the immune system plays a central role. People with active canker sores show elevated levels of inflammatory signaling molecules in their blood and an increase in certain immune cells that attack the mouth’s own tissue. There appears to be a genetic component: if your parents got frequent canker sores, you’re more likely to as well.
Common triggers include physical trauma (biting your cheek, a sharp edge on a tooth, aggressive brushing), emotional stress, hormonal shifts during menstruation, food sensitivities, and, interestingly, quitting smoking. None of these cause canker sores on their own. They act as triggers in people whose immune systems are already primed to overreact.
Realistic Healing Timeline
Pain from a minor canker sore typically peaks in the first two to three days, then gradually improves. By day four or five, eating and talking should feel noticeably easier. The ulcer itself closes over the next week or so, with full healing usually complete within 10 to 14 days. Treatment won’t make a canker sore vanish overnight, but numbing agents, protective pastes, and avoiding irritants can compress the worst of the discomfort into a shorter window. Chemical cautery products offer the fastest results, potentially cutting total healing time roughly in half.