No single treatment instantly eliminates a canker sore, but several options can cut healing time in half and dramatically reduce pain while the ulcer closes. Most canker sores heal on their own within two weeks. The right combination of topical treatments, rinses, and nutritional support can speed that timeline and keep sores from coming back.
Salt Water and Baking Soda Rinses
The simplest and cheapest option is a salt water rinse. Salt draws fluid out of the inflamed tissue, which reduces swelling and creates a less hospitable environment for bacteria. Mix 1 teaspoon of salt into 4 cups (one quart) of water, swish for 15 to 30 seconds, then spit. You can do this every 4 to 6 hours.
Baking soda works similarly by neutralizing acids in the mouth that irritate the open sore. Use the same ratio: 1 teaspoon of baking soda per quart of water. You can also combine both, using 1 teaspoon of salt and 1 teaspoon of baking soda in one quart of water. Use lukewarm water, not hot or cold, and avoid swallowing the rinse.
Over-the-Counter Pain Relief
Benzocaine is the most widely available topical numbing agent for canker sores. It’s found in gels and pastes you apply directly to the ulcer, and it works by temporarily blocking nerve signals in the area. The relief is fast but short-lived, usually lasting 15 to 30 minutes. Reapply as directed on the packaging, typically before meals so you can eat without pain.
Hydrogen peroxide rinses act as oral wound cleansers. Products marketed for mouth sores typically contain 1.4% hydrogen peroxide. You swish about 10 ml (one capful) over the affected area for at least one minute, then spit. This helps remove dead tissue and debris from the ulcer surface, keeping it clean so it can heal faster. Use up to four times daily after meals and at bedtime.
Chemical Cautery: The Fastest Option
If you want something that comes closest to “killing” a canker sore in one shot, chemical cautery is it. A prescription product called Debacterol chemically burns the surface of the ulcer, sealing it and reducing healing time to about a week. Your dentist or doctor applies it directly to the sore in a single visit. It stings intensely for a few seconds, then pain drops significantly.
Silver nitrate is another cautery option. It hasn’t been shown to speed healing the way Debacterol does, but it can provide meaningful pain relief by destroying the exposed nerve endings on the ulcer’s surface.
Prescription Steroid Treatments
For larger or more painful sores, prescription topical steroids reduce the inflammatory response that makes canker sores hurt. These come as gels you apply directly to the sore or as a steroid mouth rinse for people dealing with multiple sores at once. The steroids suppress the immune overreaction happening at the ulcer site, which both eases pain and helps tissue repair itself faster.
Laser Treatment for Severe Sores
Dental lasers are increasingly used for canker sores that are large, unusually painful, or keep recurring. A meta-analysis of clinical trials found that laser therapy reduced pain significantly compared to placebo and shortened healing time by nearly 6 days on average. The procedure takes just a few minutes, and many patients report immediate pain relief. It works by sterilizing the wound surface and stimulating tissue repair. Ask your dentist if they offer low-level laser therapy for oral ulcers.
Alum Powder as a Home Remedy
Alum powder (potassium aluminum sulfate) is a common home remedy that works as an astringent, causing the tissue to contract and tighten. This helps dry out the sore and can reduce its size. To use it, dab a small amount directly onto the canker sore, let it sit for about a minute, then rinse your mouth thoroughly.
Be aware that alum can cause tingling, tightness, and dryness, especially on broken skin like an open ulcer. Don’t swallow it, as it can cause nausea and stomach upset. People with sensitive skin or aluminum allergies should skip this one.
Nutrient Deficiencies That Cause Recurring Sores
If you’re getting canker sores repeatedly, the cause may be nutritional rather than local. There is strong evidence linking recurrent canker sores to deficiencies in vitamin B12, folate, and vitamin C. Correcting these deficiencies often reduces or stops the cycle entirely.
For B12, effective supplementation ranges from 500 to 1,000 mcg daily by mouth. Folate deficiency responds to 400 to 800 mcg daily for mild cases, with higher doses for more severe depletion. Vitamin C deficiency calls for 100 to 500 mg daily in mild cases. If you get canker sores more than a few times a year, a blood test checking these levels is a practical first step. Older adults are especially prone to B12 deficiency because absorption decreases with age.
What to Avoid While Healing
Acidic foods like citrus, tomatoes, and vinegar-based dressings directly irritate the open ulcer and can slow healing. Spicy foods, crunchy chips, and hard bread edges cause mechanical damage to the sore. Switching to softer, blander foods for a few days makes a noticeable difference in pain levels and recovery speed.
Toothpastes containing sodium lauryl sulfate (SLS), a foaming agent, have been associated with canker sore flare-ups in some people. Switching to an SLS-free toothpaste is a low-effort change worth trying if you get sores frequently.
Canker Sores vs. Cold Sores
These are completely different conditions that require different treatments. Canker sores appear inside the mouth as single, round white or yellow ulcers with a red border. They are not contagious. Cold sores (fever blisters) appear outside the mouth, usually around the lip border, as clusters of small fluid-filled blisters. Cold sores are caused by herpes simplex virus and are highly contagious. If your sore is on the outside of your lip and looks like a blister, the treatments in this article won’t help. You need an antiviral medication instead.