Most canker sores heal on their own in 10 to 14 days without any treatment. That’s the timeline for the common, small variety that accounts for the vast majority of cases. But the type and size of the sore matters: larger or more unusual forms can stick around for weeks or even months.
Minor Canker Sores: The Most Common Type
About 80% of canker sores are the minor type, measuring less than a centimeter across. These typically heal within 10 days and don’t leave scars. You’ll notice the pain is worst in the first few days, then gradually fades as the sore shrinks. By day seven or eight, eating and talking usually feel much more comfortable, even if the sore is still visible.
Before the sore itself appears, you may feel a burning or tingling sensation in the spot for one to two days. This prodromal phase is a heads-up that a sore is forming, and it’s the window where early treatment can make the biggest difference.
Major Canker Sores: Weeks to Months
Major canker sores are less common but significantly more disruptive. They measure roughly half an inch to over an inch across, are deeper than minor sores, and have irregular edges. These can take many weeks to heal, and in some cases persist for months. Unlike their smaller counterparts, major sores frequently leave scars once they finally close up. The pain tends to be more intense and can interfere with eating, drinking, and speaking for the entire duration.
Herpetiform Canker Sores: Clusters That Merge
The rarest type, herpetiform canker sores, looks very different from the others. Instead of one or two sores, you develop many tiny ulcers at once, sometimes up to 100 in a single episode. These small sores fuse together over time into larger, irregularly shaped ulcers that typically last about two weeks. Despite the name, they have nothing to do with the herpes virus.
What Affects How Fast You Heal
Several factors influence whether your sore clears up in a week or lingers closer to three. Location plays a role: sores on the tongue or soft palate tend to hurt more and can feel like they take longer because of constant friction from talking and chewing. Repeated irritation from braces, sharp tooth edges, or accidentally biting the same spot can also slow healing or trigger new sores nearby.
Your overall health matters too. Stress, poor sleep, and nutritional gaps (particularly in iron, B12, and folate) are well-known triggers and can extend healing time. People who get frequent canker sores often notice that outbreaks cluster during stressful periods or after illness.
Treatments That Shorten the Timeline
You can’t make a canker sore disappear overnight, but certain treatments meaningfully speed things up. Over-the-counter options include protective pastes that coat the sore and numbing gels that reduce pain while you eat. Antiseptic mouth rinses can help prevent secondary infection, which would otherwise delay healing.
For faster results, some dentists offer chemical cauterization with silver nitrate. In clinical trials, patients treated with silver nitrate reported pain resolution in just over one day on average, compared to nearly five days with a placebo. Healing time dropped as well: treated sores closed in about 2.7 days for the majority of patients, versus 5.5 days without treatment. By the seventh day after the procedure, 60% of treated patients had fully healed sores, compared to 32% in the placebo group. It’s a quick in-office procedure, not something you do at home.
Prescription options like steroid mouth rinses or gels can also reduce inflammation and shorten healing, particularly for people who get frequent or severe outbreaks.
When a Sore Lasts Too Long
A canker sore that hasn’t healed after three weeks deserves professional attention. Guidelines in both the UK and US use the three-week mark as the threshold for specialist referral, because a non-healing mouth ulcer can occasionally signal something more serious, including oral cancer.
There are a few practical differences between a lingering canker sore and something concerning. Canker sores are painful from the start and become less painful as they heal. Oral cancers in their earliest stages are typically not painful. Canker sores are flat against the surrounding tissue, while oral cancers often have a small lump or bump beneath the surface that you can feel with your tongue or finger. A spot that grows larger over time, changes from white to red, or starts bleeding when it didn’t before warrants a closer look.
For recurrent canker sores (those that keep coming back every few weeks or months), a doctor may check for underlying conditions like celiac disease, inflammatory bowel disease, or vitamin deficiencies that can drive repeated outbreaks.