Most canker sores heal on their own within 10 to 14 days without any treatment. The pain typically peaks in the first few days and gradually fades as the sore closes up, with many people noticing significant relief by day five or six. However, the timeline varies quite a bit depending on the size and type of sore you’re dealing with.
Healing Time by Type of Canker Sore
Not all canker sores follow the same clock. There are three distinct types, and each has a very different recovery window.
Minor canker sores are the most common, making up roughly 80% of cases. They’re small, usually under a centimeter across, and oval-shaped with a white or yellowish center. These resolve within 10 to 14 days and don’t leave scars.
Major canker sores are larger than one centimeter, deeper, and significantly more painful. These can take weeks or even months to fully heal, and they often leave scars behind. If you have a sore that’s unusually large and still going strong after two weeks, this is likely what you’re dealing with.
Herpetiform canker sores are the rarest type. They appear as clusters of tiny ulcers, sometimes dozens at once (up to 100 in severe cases), that can merge into larger, irregular sores. Despite the name, they have nothing to do with the herpes virus. Their healing time is similar to minor sores, though the merging and sheer number can make the experience feel longer and more painful.
What the Healing Process Looks Like
Canker sores move through a predictable sequence of stages. Knowing where you are in that sequence can help you gauge how much longer you have to wait.
The first stage is a tingling or burning sensation, usually lasting a day or two before the sore actually appears. You might feel a slight bump or rough patch on the inside of your lip, cheek, or tongue. This is the best window to start any topical treatment if you plan to use one.
Next comes the ulcerative stage, when the sore opens up and becomes a visible crater. This is the most painful phase, typically lasting three to five days. Eating acidic, salty, or spicy foods will be noticeably uncomfortable. The sore will have a white or yellow center surrounded by a red border.
After the worst of the pain passes, the healing stage begins. The sore gradually shrinks from the edges inward as new tissue forms. You’ll notice the redness fading and the pain becoming more of a dull irritation than a sharp sting. Within another five to seven days, the surface closes over completely, entering the remission phase with no trace left behind (for minor sores, at least).
What Slows Down Healing
If your canker sore seems to be hanging around longer than two weeks, a few common factors could be dragging things out. Repeated irritation is the biggest culprit. Biting the same spot, brushing too aggressively over the sore, or eating rough-textured foods like chips and crusty bread can reopen the wound and reset the healing clock.
Nutritional deficiencies also play a role. Low levels of vitamin B12, iron, and folate are linked to recurrent canker sores and slower recovery. Researchers have specifically studied whether supplementing with B12 can reduce how often sores come back and how severe they are when they do. If you’re getting canker sores frequently, it’s worth looking at whether your diet is short on these nutrients.
Stress and poor sleep suppress your immune response, which can extend healing time. Hormonal shifts, particularly around menstruation, are another well-documented trigger. And certain toothpastes containing sodium lauryl sulfate, a foaming agent, can irritate the tissue inside your mouth and slow recovery. Switching to an SLS-free toothpaste is one of the simplest changes you can make.
How to Reduce Pain While You Wait
Over-the-counter topical gels containing benzocaine numb the area and make eating more tolerable. They don’t speed up healing, but they take the edge off during the worst days. Apply them directly to the sore before meals for the best effect.
Rinsing with warm salt water (about half a teaspoon in a cup of water) several times a day helps keep the area clean and can reduce inflammation. Some people find that holding a small ice chip against the sore provides temporary relief as well.
Avoiding certain foods makes a real difference in day-to-day comfort. Citrus fruits, tomatoes, vinegar-based dressings, and anything with sharp edges will aggravate the sore. Soft, cool, bland foods are your best bet until the ulcerative phase passes.
When a Sore Lasts Too Long
A canker sore that hasn’t healed after two weeks deserves attention. Large, persistent, or unusually painful sores sometimes need prescription treatment, such as stronger anti-inflammatory rinses or corticosteroid gels that a dentist or doctor can provide.
It’s also important to know that not every mouth ulcer is a canker sore. Oral cancers can appear as painless or slow-growing ulcers that don’t heal. A sore that persists beyond three weeks, keeps growing, or is accompanied by unexplained weight loss, difficulty swallowing, or a lump in the neck should be evaluated promptly. A simple visual exam, and occasionally a biopsy, can rule out anything serious.