Most canker sores heal on their own within 5 to 14 days. About 80% of people who get canker sores develop the minor type, which is smaller than 1 cm and disappears without leaving a scar. The timeline can stretch significantly longer, though, depending on which type you’re dealing with.
The Typical Healing Timeline
A canker sore goes through a predictable sequence. Before anything is visible, you’ll feel a tingling or burning sensation for a few hours. The spot turns red, swells slightly, and becomes painful. Within one to three days, the swelling develops into the characteristic whitish spot with a red border. Pain peaks during this stage and then gradually fades over the next few days. By about one week, most minor canker sores are completely gone.
Some minor sores take the full 14 days, especially if they’re irritated by food, braces, or repeated contact with your teeth. The pain typically resolves before the sore itself disappears, so you may stop noticing it a few days before it’s fully healed.
Major and Herpetiform Canker Sores Take Longer
Not all canker sores follow that one-to-two-week timeline. About 10% of people who get recurrent canker sores develop the major type, which exceeds 1 cm in diameter and can appear on parts of the mouth that minor sores don’t usually affect. These can take up to six weeks to heal and occasionally leave a scar, though scarring is uncommon.
The rarest form, herpetiform canker sores, affects roughly 1 to 10% of people with recurrent outbreaks. Despite the name, these aren’t related to herpes. They start as many tiny ulcers (sometimes up to 100 at once) that fuse together into larger, irregularly shaped sores. Their healing time is closer to the minor type, but the sheer number of sores makes the experience more painful and drawn out.
Recurrence Patterns Vary Widely
How often canker sores come back matters as much as how long each one lasts. People with milder recurrence tend to get outbreaks two to three times per year, with sores that are minimally painful and resolve in two to three days without treatment. People with more frequent or severe recurrence experience sores that last up to 10 days per episode and cause more significant pain.
If you’re someone who gets canker sores regularly, your pattern is worth tracking. Frequent, prolonged episodes may point to an underlying trigger worth addressing.
What Speeds Up Healing
Canker sores resolve on their own, but you can shorten the process. Rinsing with salt water or a baking soda solution (1 teaspoon of baking soda in half a cup of warm water) helps relieve pain and may support faster healing. Avoiding acidic, spicy, or rough-textured foods reduces irritation to the sore while it’s open.
For sores that are particularly painful or slow to heal, over-the-counter pastes containing anti-inflammatory ingredients can help. In clinical trials, prescription-strength anti-inflammatory pastes dropped pain scores from about 6 out of 10 down to 2 out of 10 by day three, with noticeable reductions in sore size by day five. If over-the-counter options aren’t cutting it, a dentist or doctor can prescribe something stronger.
Nutritional Deficiencies and Recurrent Sores
People who get canker sores repeatedly tend to have lower intake of vitamin B12 and folate. In one study comparing people with recurrent canker sores to the general population, the canker sore group consumed about 7% less of the recommended daily B12 and 20% less folate. Broader research has found nutritional deficiencies, particularly B12, folate, and iron, in roughly 14 to 18% of people with recurrent canker sores.
Correcting these deficiencies through diet or supplements has been shown to improve symptoms and reduce the frequency of outbreaks. This won’t make a current sore heal overnight, but if you’re dealing with canker sores every few weeks, it’s worth looking at whether your diet is falling short on these nutrients.
Canker Sores vs. Cold Sores
If you’re unsure whether you have a canker sore or a cold sore, location is the simplest way to tell. Canker sores form inside the mouth, on soft tissues like the inner cheeks, gums, or tongue. Cold sores (fever blisters) appear on the outside of the mouth, typically around the lips. Cold sores are caused by the herpes simplex virus and are contagious. Canker sores are not contagious and have no viral cause.
Both types generally resolve without treatment, but their timelines and triggers are different. If your sore is on the outside of your lip and started as a cluster of small blisters, it’s almost certainly a cold sore, not a canker sore.
When a Canker Sore Lasts Too Long
A canker sore that hasn’t healed after two weeks deserves attention. An oral ulcer that persists beyond three to four weeks may require a biopsy to rule out other conditions, including oral cancer. Sores that are unusually large, spreading, or accompanied by fever also fall outside the normal pattern. A single sore that won’t go away is more concerning than frequent but short-lived sores, so don’t assume a long-lasting ulcer is just a stubborn canker sore.