Most canker sores heal on their own within 7 to 14 days. If yours has lingered beyond two weeks, that’s outside the normal window and worth paying attention to. The exact timeline depends on which type of canker sore you’re dealing with, since they range from tiny surface-level irritations to deep, crater-like ulcers that can persist for over a month.
Healing Timelines by Type
There are three types of canker sores, and each follows a different clock.
Minor canker sores account for the vast majority of cases. They measure 5 to 10 millimeters across, roughly the size of a pencil eraser or smaller. These heal spontaneously in 7 to 14 days and don’t leave scars. If you’ve had a canker sore before, this is almost certainly the type you had.
Major canker sores are larger (1 to 3 centimeters), deeper, and far more painful. They can last anywhere from 10 days to 6 weeks, sometimes longer. About 64% of them heal with scarring because of how deeply they penetrate the tissue. These are uncommon, but if you’re dealing with a sore that’s unusually large and has been around for weeks, this may be what you have.
Herpetiform canker sores show up as clusters of tiny pinpoint ulcers, sometimes dozens at once. Despite the name, they have nothing to do with herpes. Individual ulcers in a cluster typically last one to two weeks, though the full episode can take up to a month to fully resolve. Scarring is rare.
What the Healing Process Feels Like
Before the sore itself appears, many people notice a tingling or burning sensation in the spot where it’s about to form. This prodromal phase is actually the best window to intervene, since treating the area at this stage can sometimes prevent the ulcer from fully developing.
Once the sore opens up, you’re in the most painful stretch. The ulcer is typically a shallow white or yellowish oval with a red border. Pain tends to peak in the first few days, then gradually fades as new tissue forms. By the end of the first week, a minor canker sore is usually noticeably smaller and less tender. By day 10 to 14, the surface has closed over completely.
People who get canker sores regularly tend to fall into two patterns. Some experience episodes just a few times a year, with outbreaks lasting only a few days. Others deal with monthly flare-ups lasting 3 to 10 days each. If yours follow a recurring pattern, tracking the frequency can help you identify triggers.
What Slows Healing Down
If your canker sores seem to take longer than they should, or keep coming back, nutritional deficiencies are one of the most well-documented causes. Screening studies have found that 14 to 18% of people with recurring canker sores are low in vitamin B12, folate, or iron. Both B12 and folate play roles in building new cells and forming healthy blood, and sometimes mouth ulcers are the earliest visible sign of a deficiency, appearing before other symptoms do. Correcting the deficiency through supplementation typically improves the condition.
Other factors that can delay healing or trigger new sores include mechanical trauma (biting your cheek, rough toothbrush use, sharp edges on dental work), stress, hormonal shifts, and certain acidic or spicy foods. Toothpaste containing sodium lauryl sulfate, a common foaming agent, has also been linked to more frequent outbreaks in some people. Switching to an SLS-free toothpaste is a simple experiment worth trying.
Do Home Remedies Actually Speed Things Up?
Saltwater rinses are the most commonly recommended home treatment, and there’s real evidence behind them. Lab research on human gum tissue cells found that rinsing with a saline solution significantly promoted cell migration, the process by which new cells move into a wound to close it. The rinse also increased production of collagen and other structural proteins that rebuild tissue. The practical takeaway: mix about one teaspoon of salt into a cup of warm water and rinse for two minutes, three times a day. This won’t eliminate the sore overnight, but it creates a better environment for healing and helps keep the area clean.
Over-the-counter numbing gels and protective pastes can reduce pain and shield the sore from further irritation, though they don’t dramatically change the overall healing timeline. Their value is mainly in making the worst days more tolerable.
When Treatment Makes a Real Difference
Prescription-strength topical steroid ointments can meaningfully shorten how long a canker sore sticks around. In clinical trials, one steroid paste cut ulcer duration from about 6.8 days down to 3.5 days compared to a placebo. Another trial found that 70% of people using a topical steroid healed in under 6 days, compared to 47% with placebo. Results vary across studies, with some showing only modest improvements, but the overall trend favors earlier healing when steroids are applied early in the process.
Chemical cauterization with silver nitrate is another option, typically done in a dental or medical office. In one controlled trial, 60% of patients treated with silver nitrate had fully healed ulcers by day 7, compared to 32% in the placebo group. Among those who healed, the average recovery time was 2.7 days after treatment versus 5.5 days without it. Cauterization also provides near-immediate pain relief, which is often the main reason people seek it out.
When a Canker Sore Has Lasted Too Long
The two-week mark is the key threshold. Oral lesions related to infection, inflammation, or minor trauma typically resolve within that window. If a sore persists for two weeks or longer after any obvious irritant has been removed, clinical guidelines recommend further evaluation, potentially including a biopsy. This isn’t because every lingering sore is dangerous, but because a persistent ulcer that doesn’t follow the normal healing arc needs to be distinguished from other conditions, including oral cancer, autoimmune diseases like Behçet’s syndrome, or inflammatory bowel disease that can manifest in the mouth.
Other signals that warrant a closer look: a canker sore larger than a centimeter, sores accompanied by fever, sores that spread rather than shrink, or frequent recurrences that interfere with eating or speaking. A single canker sore that heals within two weeks, even if it’s painful, is almost always nothing to worry about.