Most canker sores heal within 3 to 10 days, depending on their severity. Mild ones that cause minimal pain often resolve in 2 to 3 days on their own, while more painful sores can linger for up to 10 days. Before the visible sore even appears, you’ll typically feel a burning or prickling sensation for 1 to 3 days, which means the full experience from first tingle to complete healing can stretch closer to two weeks.
The Stages of a Canker Sore
Canker sores follow a predictable pattern. The first phase is called the prodromal stage, where you feel a burning or prickling sensation and notice a raised, reddened area on the inside of your mouth. No visible ulcer exists yet, but you can tell something is coming. This lasts 1 to 3 days.
After that, the sore breaks open into a shallow, round or oval ulcer, usually white or yellowish with a red border. This is the most painful phase, and it typically peaks within the first few days. Eating, drinking, and talking can all aggravate it. Over the next several days, a thin layer of tissue gradually covers the ulcer and pain fades. By day 7 to 10 for most sores, the surface is fully healed with no scar.
Mild vs. Severe Canker Sores
Not all canker sores follow the same timeline. The mild type, which accounts for the majority of cases, tends to be small (under a centimeter), minimally painful, and clears up in 2 to 3 days without any treatment. Most people who get canker sores experience this type a few times per year.
The more painful version can last up to 10 days and tends to interfere more with eating and speaking. These sores are often larger, deeper, and slower to close. In rare cases, people develop major aphthous ulcers, which are significantly bigger, can take weeks or even months to heal, and sometimes leave scars. These are uncommon enough that if you’ve had one, you likely already know you’re dealing with something beyond a typical canker sore.
What Triggers Them
Canker sores usually start with a minor injury to the soft tissue inside your mouth. Biting your cheek, scraping your gums with a chip, or irritation from braces can all create the tiny wound that turns into an ulcer. Under normal circumstances, these small injuries heal quickly. But when your body is under stress, or you’re low on certain nutrients like folate, iron, zinc, or vitamin B12, those tiny injuries are more likely to develop into full canker sores.
Certain foods also play a role. Citrus fruits, spicy dishes, and acidic vegetables can irritate the mouth lining and either trigger new sores or make existing ones worse. One less obvious culprit is sodium lauryl sulfate (SLS), a foaming agent found in many toothpastes. Switching to an SLS-free toothpaste is one of the simplest changes you can make if you get canker sores frequently.
How to Speed Up Healing
You can’t make a canker sore disappear overnight, but several approaches can shorten its lifespan and reduce pain in the meantime.
Saltwater rinses are the simplest option. Dissolving salt in warm water and swishing it around your mouth reduces acidity and inflammation, which helps the sore heal faster. Baking soda rinses work through a similar mechanism. Neither will sting as much as you might expect, and both are worth doing several times a day.
Honey, particularly manuka honey, has stronger evidence behind it. Applying it directly to the sore several times daily can reduce pain, shrink the ulcer, and promote faster tissue repair. Its natural antibacterial and anti-inflammatory properties make it one of the more effective home remedies available. Coconut oil, swished in the mouth for about 10 minutes daily, may also help thanks to its antibacterial effects.
For sores that are especially painful or slow to heal, prescription topical treatments can help. Steroid-based pastes applied directly to the ulcer reduce inflammation and can shorten healing time. They won’t prevent future sores from forming, but they make the current one less miserable and quicker to resolve.
When a Canker Sore Lasts Too Long
The American Academy of Oral Medicine recommends that any mouth ulcer lasting more than 10 to 14 days be evaluated by a dentist. A sore that hasn’t begun healing in two weeks may not be a simple canker sore at all. Other conditions, including infections and oral cancers, can look similar in the early stages. A dentist can examine the sore and, if needed, take a small tissue sample to rule out anything more serious. This is especially important if the sore is unusually large, spreading, or accompanied by fever or difficulty swallowing.