Most canker sores heal on their own within 5 to 14 days. That timeline applies to about 80% of people who get them, since the vast majority develop the smaller, more common type. Larger or less common types can take significantly longer, sometimes up to six weeks.
The Three Types and Their Timelines
Not all canker sores follow the same clock. The type you have determines how long you’ll be dealing with it.
Minor canker sores are the most common, making up roughly 80% of cases. They’re smaller than 1 centimeter (about the size of a pea or smaller), and they heal within 5 to 14 days without leaving a scar. If you’ve had canker sores before, this is almost certainly the type you’ve experienced.
Major canker sores are larger than 1 centimeter and go deeper into the tissue. These can persist for up to 6 weeks. While they rarely leave a permanent scar, the healing process is noticeably slower and more uncomfortable.
Herpetiform canker sores are the least common type. They appear as clusters of tiny ulcers that can merge together into larger, irregular sores. When ulcers fuse like this, scarring becomes more likely.
What Each Stage Feels Like
A canker sore doesn’t just appear and disappear. It moves through distinct stages, and knowing where you are in the process helps you gauge how much longer you have to go.
The first hint is a tingling, burning, or prickling sensation in one spot inside your mouth, usually about 24 hours before anything is visible. This is followed by a pre-ulcerative stage lasting roughly 18 hours to 3 days, where the area turns red and slightly swollen but hasn’t broken open yet.
Then comes the ulcerative stage, which is the painful part. The sore opens up into a shallow, round or oval crater, typically white or yellowish with a red border. This active ulceration phase lasts anywhere from 1 to 16 days, and pain tends to peak within the first few days. The healing stage follows, lasting 4 to 35 days, though it usually wraps up within 3 weeks. During healing, pain gradually fades and the tissue closes over.
For a typical minor canker sore, the worst discomfort is usually in the first 3 to 5 days. By days 7 to 10, most people notice the sore shrinking and hurting less.
What Can Speed Things Up
There’s no cure that makes a canker sore vanish overnight, but a few approaches can shorten the painful window. Silver nitrate, applied by a dentist or doctor, tends to reduce pain within the first day, though it doesn’t necessarily make the sore heal faster overall. Another in-office treatment resolves symptoms more effectively, with studies showing significant pain reduction by day 3 and symptom resolution by day 6.
Over-the-counter options include topical gels and rinses that numb the area or create a protective barrier over the sore. These won’t dramatically cut healing time, but they make eating and talking less miserable while your body does the repair work.
One simple change that actually affects healing duration: switching to a toothpaste without sodium lauryl sulfate (SLS), the foaming agent in most toothpastes. A systematic review of clinical trials found that using SLS-free toothpaste reduced not just how often canker sores came back, but also how long each sore lasted and how much it hurt. If you get canker sores regularly, this is one of the easiest interventions to try.
Why Some Sores Take Longer to Heal
If your canker sores seem to linger beyond the typical two-week window, a nutritional deficiency could be slowing things down. Studies have found that roughly 14 to 18% of people with recurring canker sores are deficient in vitamin B12, iron, or folate. When those deficiencies are corrected through supplementation, canker sores often improve noticeably, sometimes quickly enough to suggest the vitamins are acting directly on the mouth tissue rather than through a slow, systemic effect.
Stress, hormonal shifts, and immune suppression also play a role. A canker sore is essentially your immune system creating inflammation against your own mouth lining, so anything that disrupts immune function can extend the process. Mechanical trauma matters too. If a sore sits right where your teeth rub against your cheek or where a retainer presses, repeated irritation can restart the healing clock.
When a Sore Lasting Too Long Is a Warning Sign
The two-week mark is the key threshold. If a canker sore hasn’t healed after two weeks, it’s worth having a healthcare provider look at it. The same goes for sores larger than a centimeter, sores that come with fever or flu-like symptoms, sores that keep coming back multiple times a year, or sores painful enough to interfere with eating or drinking. These patterns could point to an underlying condition driving the ulcers, or in rare cases, the sore may not be a canker sore at all and may need a biopsy to rule out something more serious.