Most canker sores heal on their own within 5 to 14 days. The exact timeline depends on which type you have, since canker sores come in three varieties that differ significantly in size, severity, and how long they stick around. The small, common type clears up in under two weeks. Larger or more complex sores can linger for weeks.
Minor Canker Sores: 5 to 14 Days
The vast majority of canker sores fall into the “minor” category. These are small, round or oval ulcers less than 1 cm across, and they heal within two weeks without leaving a scar. Pain tends to be worst in the first few days, often flaring when you eat or drink something acidic or salty. By about day 7, most people notice the soreness fading even though the ulcer is still visible. The sore gradually shrinks from the edges inward until the tissue looks normal again.
Major Canker Sores: 5 to 10 Weeks
About 10% of people who get canker sores develop the major type, which is larger than 1 cm in diameter. These are deeper, more painful, and take dramatically longer to resolve. Major canker sores can persist for 5 to 10 weeks and often leave scarring once they finally close. They tend to appear on the lips, soft palate, or back of the throat, where the tissue is softer and heals more slowly. If your sore is unusually large or has lasted more than two weeks, this is likely the type you’re dealing with.
Herpetiform Canker Sores: 1 to 2 Weeks
Herpetiform canker sores are the least common type. Despite the name, they have nothing to do with the herpes virus. They show up as clusters of tiny ulcers that can merge into one larger, irregular sore. Each cluster typically heals within one to two weeks and doesn’t scar. The “herpetiform” label just describes their appearance, which resembles herpes lesions at a glance.
Why Some Sores Take Longer to Heal
Location matters. Sores on the tongue or inner cheek get constantly irritated by chewing and talking, which can slow things down. A canker sore tucked inside the lower lip, where it’s relatively sheltered, tends to heal faster than one on the side of the tongue.
Nutritional deficiencies also play a real role. Studies have found that people with recurring canker sores are more likely to have low levels of vitamin B12 and folate. Roughly 14 to 18% of people with recurrent canker sores show some kind of nutritional deficiency on blood work. When those gaps are corrected through supplementation, both the frequency and duration of outbreaks often improve. Researchers believe these vitamins have a direct effect on the health of the mouth’s lining, though the exact mechanism isn’t fully understood.
Repeated trauma to the same spot, like a sharp tooth edge or ill-fitting dental appliance rubbing against tissue, can keep a sore from closing. Stress and hormonal shifts are also well-established triggers that can both spark new sores and drag out healing.
When Pain Ends vs. When the Sore Disappears
Pain and healing don’t follow the same clock. For minor canker sores, the sharp, stinging pain usually peaks within the first 3 to 4 days and then steadily decreases. By the time you’re a week in, eating is typically much more comfortable. But the visible ulcer itself, that white or yellowish crater with a red border, often lingers a few days after the pain has essentially stopped. So if you can still see the sore but it no longer hurts, that’s normal. It’s in its final stage of healing.
For people who get canker sores monthly, the painful phase of each episode usually lasts 3 to 10 days. Some people experience near-constant cycles where a new sore appears before the last one has fully healed, which can make it feel like the problem never ends.
What Helps Them Heal Faster
You can’t make a canker sore vanish overnight, but a few things can shave days off the process and reduce pain in the meantime. Over-the-counter oral gels that form a protective film over the sore help shield it from food and saliva, letting tissue repair itself without constant irritation. Rinsing with warm salt water several times a day keeps the area clean and can reduce inflammation.
Avoiding acidic foods (citrus, tomatoes, vinegar-based dressings) and spicy dishes prevents the repeated chemical irritation that slows healing. The same goes for crunchy foods like chips or toast, which can physically re-injure the sore.
If you get canker sores frequently, it’s worth paying attention to your intake of B12 and folate. Leafy greens, eggs, fortified cereals, and meat are good dietary sources. Correction of a deficiency, when one exists, is one of the few interventions shown to meaningfully reduce how often sores return and how long they last.
Sores That Last Beyond Two Weeks
A canker sore that hasn’t healed within two weeks, or one that’s unusually severe, warrants a visit to a doctor or dentist. Most of the time, a slow-healing sore is simply a major canker sore running its longer natural course. But oral ulcers that won’t close can occasionally signal other conditions, including autoimmune disorders, infections, or, rarely, oral cancer. A healthcare provider can visually evaluate the sore and, if needed, take a small tissue sample to rule out anything more serious.