Most mouth ulcers heal on their own within 7 to 14 days without any treatment. The exact timeline depends on the type and size of the ulcer, but the vast majority are minor canker sores that resolve completely in about two weeks and don’t leave a scar. Larger or deeper ulcers can take significantly longer.
Healing Time by Ulcer Type
Mouth ulcers come in three categories, and the size of the ulcer is the biggest factor in how long you’ll be dealing with it.
Minor ulcers are by far the most common. They’re small (under 1 cm across), shallow, and typically show up on the inside of your cheeks, lips, or on the soft palate. These usually heal within 7 to 14 days on their own, and they don’t scar.
Major ulcers are larger and deeper. They can take 4 to 6 weeks to fully heal and often leave some scarring behind. If you have a single large ulcer that seems to be growing rather than shrinking, this is the type worth getting checked out.
Herpetiform ulcers appear as clusters of many small sores that can merge together. Despite their name, they’re not caused by the herpes virus. They tend to heal in 2 to 4 weeks, though the clusters can be particularly painful while they last.
What Healing Looks and Feels Like
Mouth ulcers go through the same basic healing stages as any wound, just faster because the mouth’s lining regenerates quickly. In the first few days, you’ll notice the most pain, redness, and swelling. This is the inflammatory phase, where your immune system sends white blood cells to clear out debris and fight off bacteria. The ulcer typically looks like a round white or yellow sore with a red border during this stage.
After about 3 to 5 days, pain usually starts decreasing as new tissue forms to replace what was lost. You may notice pinkish or whitish granular tissue filling in the center of the ulcer. Blood vessels grow into the area to deliver oxygen and nutrients, and the wound gradually closes as cells multiply. By the end of the second week for minor ulcers, the surface is fully covered with new tissue. In the final phase, collagen fibers strengthen and reorganize the healed area, and any remaining redness fades.
Canker Sores vs. Cold Sores
It’s worth making sure you’re actually dealing with a canker sore (aphthous ulcer) and not a cold sore, since the two have different causes and slightly different timelines. Canker sores appear inside the mouth as a single round white or yellow sore with a red border. Cold sores show up on the outside of the mouth, around the lips, and look like clusters of small, fluid-filled blisters. Cold sores are caused by the herpes simplex virus and are contagious. Canker sores are not contagious and their exact cause isn’t fully understood, though stress, minor injuries, acidic foods, and nutritional deficiencies can trigger them.
What Helps Them Heal Faster
Salt water rinses are one of the simplest and most effective home treatments. Lab research published in PLOS One found that rinsing with a saline solution significantly improved wound closure by encouraging the cells responsible for tissue repair to migrate into the wound faster. A simple rinse of about half a teaspoon of salt in a cup of warm water, swished gently a few times a day, can help keep the ulcer clean and support healing.
Beyond salt water, a few other strategies can reduce pain and avoid slowing the healing process:
- Avoid irritating foods. Spicy, acidic, or sharp-edged foods (chips, crusty bread) can re-injure the ulcer and reset the healing clock.
- Use a soft-bristled toothbrush. Brushing too aggressively near the ulcer can tear new tissue.
- Try over-the-counter numbing gels. Products containing benzocaine can reduce pain while eating or drinking.
- Consider topical corticosteroid pastes. These are available by prescription and can reduce the total number of days you have the ulcer, along with reducing pain. They don’t prevent future ulcers, but they help the current one resolve faster.
When a Slow-Healing Ulcer Needs Attention
The critical timeline to remember is 2 weeks. If a mouth ulcer hasn’t started improving noticeably by 10 to 14 days, it should be evaluated by a dentist or doctor. The American Dental Association recommends that any oral abnormality persisting beyond 10 to 14 days without a clear diagnosis warrants a biopsy or referral. This isn’t to alarm you. The vast majority of mouth ulcers are harmless. But oral cancers can initially look like a persistent ulcer, and catching them early makes a significant difference in outcomes.
Other signs that warrant a visit: ulcers that keep coming back in the same spot, ulcers accompanied by fever, ulcers so large or painful that you can’t eat or drink, or any ulcer that seems to be getting bigger rather than smaller after the first week.