Most canker sores heal within 10 to 14 days without any treatment. The smallest ones can clear up in as little as two to three days, while larger, deeper ulcers can linger for up to six weeks. How long yours lasts depends mainly on its size and type, though nutrition, stress, and how you care for it all play a role.
Healing Time by Type
Not all canker sores are the same. They fall into a few categories, and the healing timeline varies significantly between them.
Minor canker sores are by far the most common. They measure less than a centimeter across (smaller than a pea) and heal within 10 to 14 days. They don’t leave scars. Very small or superficial ones can resolve in two to three days without any intervention at all, while slightly larger ones within this category may take the full two weeks.
Major canker sores are bigger than a centimeter, noticeably deeper, and significantly more painful. These can take up to six weeks to heal and often leave scars behind. If you’ve never had a canker sore last this long before and suddenly develop one that won’t go away, it’s worth getting it looked at.
Herpetiform canker sores are the rarest type. Despite the name, they aren’t caused by the herpes virus. They appear as clusters of tiny ulcers that can merge into larger, irregular sores. Their healing timeline generally falls somewhere between the minor and major types.
What a Typical Canker Sore Feels Like Day by Day
Most people first notice a tingling or burning sensation on the inside of the lip, cheek, or tongue before anything is visible. Within a day or two, a shallow, round ulcer forms with a white or yellowish center and a red border. Pain tends to peak during the first several days, when the ulcer is fully open and exposed to food, drinks, and the movement of your mouth.
By the end of the first week, pain usually starts fading. The ulcer gradually shrinks from the edges inward as new tissue covers the wound. By days 10 to 14, the surface is fully closed and the soreness is gone. There’s no blister stage, no crusting, and no scab. The tissue simply regenerates from the outside in.
What Slows Healing Down
A canker sore that keeps getting irritated will take longer to close. Crunchy, sharp, or acidic foods (chips, citrus, tomato sauce) can re-traumatize the ulcer each time they make contact. So can accidentally biting the sore or brushing it aggressively with a toothbrush. If the sore is in a spot where your teeth or braces repeatedly rub against it, that friction alone can add days to the timeline.
Nutritional deficiencies also play a measurable role. Studies have found a surprisingly high rate of iron and B vitamin deficiencies among people who get recurrent canker sores. Thiamine (B1) deficiency in particular has been linked to increased risk. Correcting these deficiencies, either through diet or supplementation, has been shown to reduce or eliminate recurrences in most cases. If you’re getting canker sores frequently, it may be worth checking whether you’re low in iron, B12, or other B vitamins.
Stress and lack of sleep won’t directly slow a sore that’s already formed, but they weaken the immune responses that drive tissue repair. People under chronic stress often report that their canker sores seem to take longer to resolve and come back more often.
What Can Speed Things Up
You can’t make a canker sore vanish overnight, but a few approaches can shave days off the process and reduce pain in the meantime.
Salt water rinses are one of the simplest options with some evidence behind them. A study found that a salt water solution improved wound healing effectiveness compared to plain water. The key is to gargle gently rather than rubbing salt directly on the sore, which can further damage the tissue and cause unnecessary pain. A half teaspoon of salt dissolved in a cup of warm water, swished a few times a day, helps neutralize the oral environment and supports healing.
Topical prescription treatments containing anti-inflammatory ingredients can shorten healing time when applied early. Systematic reviews have confirmed that these treatments reduce the duration of ulcers compared to placebo. Over-the-counter protective pastes and gels won’t necessarily speed healing, but they create a barrier that shields the sore from irritation, which indirectly helps it close faster.
Avoiding irritants is just as important as any treatment. Switching to a soft-bristled toothbrush, skipping spicy or acidic foods until the sore heals, and using a toothpaste free of sodium lauryl sulfate (a foaming agent linked to canker sore flare-ups) can all make a noticeable difference.
When a Mouth Sore Isn’t Just a Canker Sore
Canker sores follow a predictable pattern: they show up, hurt for a week or so, and disappear on their own. A sore that doesn’t follow this script deserves attention. Current dental guidelines recommend that any mouth sore persisting beyond 10 to 14 days without a clear diagnosis should be biopsied or referred for further evaluation. This isn’t because most lingering sores are dangerous, but because oral cancers and other conditions can mimic the appearance of a canker sore early on.
Other signs that something else may be going on include a sore larger than you’ve ever had before, a sore accompanied by high fever, sores that spread rather than shrink, or ulcers that keep coming back in the same exact spot. People with weakened immune systems, including those with HIV, can experience canker sores with extremely prolonged healing times stretching into months.