Most mouth sores heal on their own within one to two weeks. The exact timeline depends on what type of sore you’re dealing with, how large it is, and whether an underlying condition is involved. A small canker sore and a cold sore follow very different paths, but both typically resolve without treatment in about the same window.
Canker Sores: 7 to 14 Days
Canker sores (aphthous ulcers) are the most common type of mouth sore. They appear as small, round, whitish or yellowish craters with a red border, usually on the inside of the cheeks, lips, or along the gums and tongue. Minor canker sores, which make up the vast majority of cases, heal within one to two weeks without leaving a scar.
The pain is usually worst during the first three to four days, then gradually fades as the sore shrinks. You’ll likely notice the most discomfort when eating acidic, spicy, or salty foods. By the end of the first week, many small canker sores are already closing up.
Major canker sores are a different story. These are larger (often over a centimeter across), deeper, and can take six weeks or longer to heal. They sometimes leave scars. If you’ve never had one before and suddenly develop a large, deep ulcer, it’s worth getting it looked at rather than waiting it out.
Cold Sores: 1 to 2 Weeks
Cold sores form on or around the lips rather than inside the mouth, and they follow a predictable pattern over roughly 14 days. On day one, you’ll feel tingling, itching, or numbness on the skin where the sore is about to appear. This early warning stage is called the prodrome, and it’s the point when antiviral treatment is most effective if you have it on hand.
Within a day or two, small fluid-filled blisters cluster together. These eventually burst, merge into an open sore, and then crust over into a scab. The scab typically falls off within six to 14 days of the start of the outbreak. Cold sores are caused by the herpes simplex virus, which stays in the body permanently, so outbreaks can recur, especially during times of stress, illness, or sun exposure.
Why Some Mouth Sores Take Longer to Heal
Several factors can slow down healing or cause sores to keep coming back. Nutritional deficiencies are one of the most overlooked culprits. Low levels of vitamin B12, folate, or iron are linked to recurring mouth ulcers and a sore, red tongue. If you’re getting canker sores frequently, it may be worth checking whether a deficiency is contributing.
Physical trauma also plays a role. Biting your cheek, brushing too aggressively, or irritation from braces or dentures can create sores that take longer to heal simply because the area keeps getting re-injured. Switching to a soft-bristled toothbrush and avoiding toothpastes containing sodium lauryl sulfate (a foaming agent that can irritate oral tissue) may help.
Stress and immune suppression consistently extend healing time. When your immune system is occupied elsewhere, whether from a cold, lack of sleep, or chronic stress, mouth sores tend to linger at the upper end of that two-week window or beyond.
What Helps Them Heal Faster
Saltwater rinses are the simplest and most accessible remedy. Dissolving half a teaspoon of salt in a cup of warm water and swishing gently a few times a day can reduce inflammation and lower acidity in the mouth, creating a better environment for healing. Baking soda rinses work through a similar mechanism. Neither is a miracle cure, but both can take the edge off pain and may modestly speed recovery.
Over-the-counter topical treatments that form a protective film over the sore can reduce pain by shielding it from food and saliva. Prescription-strength anti-inflammatory pastes applied directly to canker sores can shorten both the duration and the pain, though they work best when used early, ideally as soon as you notice the sore forming.
For cold sores specifically, antiviral creams or oral antivirals can reduce the outbreak by a day or two if started during the tingling stage. Once blisters have fully formed, antivirals are less effective at shortening the timeline, though they can still reduce discomfort.
When a Mouth Sore Signals Something Else
The two-week mark is the key threshold. If a mouth sore hasn’t improved after two weeks of home care, or if it’s getting worse, it needs professional evaluation. Most sores that overstay this window are still benign, but persistent ulcers that don’t heal are one of the early warning signs of oral cancer, particularly in people who smoke or drink heavily.
Oral lichen planus is another condition that can mimic stubborn canker sores. It causes white, lacy patches or red, eroded areas inside the mouth that persist far longer than a typical ulcer. It’s a lifelong condition, though mild forms may clear up on their own before flaring again later. The sores from lichen planus tend to appear on both sides of the mouth symmetrically, which distinguishes them from a lone canker sore.
Other red flags include sores that bleed easily, a lump or thickening in the cheek, difficulty swallowing, or numbness in the tongue or lip. A single painless ulcer that won’t heal is more concerning than a painful one, since canker sores almost always hurt. If any of these descriptions match what you’re experiencing past the two-week mark, getting an exam gives you a clear answer and, in most cases, reassurance.