Most canker sores heal on their own in one to two weeks, but a bad one, the kind that makes eating and talking miserable, needs active management to reduce pain and speed recovery. Major canker sores can be deeper, larger than a centimeter, and take up to six weeks to heal if left untreated. The good news: a combination of rinses, topical treatments, and a few smart changes can make a real difference in how fast you recover and how much you suffer in the meantime.
Salt Water and Baking Soda Rinses
The simplest and cheapest thing you can do right now is rinse. Dissolve 1 teaspoon of baking soda in half a cup of warm water and swish it around the sore for 30 to 60 seconds, then spit. You can also use a basic salt water rinse at a similar ratio. Do this several times a day, especially after meals, to keep the area clean and reduce the acidic environment that irritates the ulcer. These rinses won’t dramatically shorten healing time, but they lower pain and help prevent a secondary bacterial infection from making things worse.
Over-the-Counter Topical Treatments
For a canker sore that’s actively painful, look for an OTC product containing benzocaine (a numbing agent) or a protective paste that forms a barrier over the sore. Numbing gels work within minutes and can make eating tolerable again, though the relief is temporary and you’ll need to reapply. Protective pastes, sometimes sold as oral wound rinses or patches, coat the ulcer and shield it from food and saliva, which reduces irritation throughout the day.
Hydrogen peroxide diluted to half strength (equal parts 3% peroxide and water) applied directly with a cotton swab is another option. It cleans the sore and may reduce bacteria around it. Avoid swallowing the solution.
When a Bad Sore Needs Prescription Help
If your canker sore is larger than a pea, extremely deep, or not improving after a week of home care, a prescription steroid rinse can make a significant difference. Dentists and doctors commonly prescribe a steroid mouthwash that you swish for one minute and spit out four times daily: after each meal and before bed. You avoid eating or drinking for 30 minutes afterward so the medication stays in contact with the tissue. These rinses reduce inflammation at the site, which both eases pain and can shorten healing time for severe ulcers.
Another clinical option is chemical cauterization with silver nitrate. In a controlled trial, 70% of patients treated with a single application of silver nitrate had a meaningful reduction in pain severity within one day, compared to just 11% in the placebo group. The pain relief lasted for the duration of the sore. It didn’t significantly shorten healing time, but for a canker sore so painful you can barely function, fast pain relief is the priority.
Avoid Irritating the Sore Further
What you put in your mouth matters. Acidic foods like citrus, tomatoes, and vinegar-based dressings directly irritate the open tissue and can make a bad sore feel dramatically worse. Spicy food, crunchy chips, and hard bread edges do the same thing mechanically. While the sore is active, stick to softer, blander foods and drink through a straw if the sore is in a spot where liquids wash over it.
Your toothpaste could also be making things worse. A systematic review found that switching from toothpaste containing sodium lauryl sulfate (SLS), a common foaming agent, to an SLS-free version significantly reduced the number of ulcers, their duration, the pain they caused, and how often they came back. Check the ingredients list on your tube. Sensodyne and a few other brands make SLS-free versions that are widely available.
Nutritional Gaps That Fuel Recurrence
If you’re dealing with canker sores that keep coming back or are unusually severe, your diet may be part of the problem. People with recurrent canker sores consistently show lower intake of vitamin B12 and folate compared to people who rarely get them. Iron deficiency is also linked to recurrence, though less commonly. Studies show that correcting these deficiencies through supplementation or dietary changes leads to measurable improvement in symptoms.
You don’t necessarily need blood work to act on this. Foods rich in B12 (meat, fish, eggs, dairy), folate (leafy greens, legumes, fortified grains), and iron (red meat, spinach, lentils) are worth emphasizing if canker sores are a recurring pattern for you. If you eat a restricted diet or suspect a deficiency, a simple blood panel from your doctor can confirm it.
How to Tell It’s Actually a Canker Sore
Canker sores are sometimes confused with cold sores, but they’re different conditions. Canker sores appear inside the mouth and look like a single round white or yellow sore with a red border. Cold sores (fever blisters) appear on the outside of the mouth, usually around the lip border, and look like clusters of small fluid-filled blisters. Cold sores are caused by the herpes simplex virus and are contagious. Canker sores are not contagious and have no viral cause.
A sore inside your mouth that lasts longer than two weeks, is larger than a centimeter, comes with fever or flu-like symptoms, interferes with eating and drinking, or recurs two to three times a year warrants a call to your doctor or dentist. Major canker sores can leave scarring and may need more aggressive treatment. Persistent mouth ulcers that don’t follow normal healing patterns can also occasionally signal other conditions that need to be ruled out.