A mouth ulcer is a small, open sore that forms on the soft tissue inside your mouth, such as the inner cheeks, gums, tongue, or the floor of the mouth. These sores are usually round or oval with a white or yellow center and a red border. Most are harmless and heal on their own within 10 to 14 days, but they can make eating, drinking, and talking surprisingly painful while they last.
Mouth ulcers are extremely common. Estimates suggest they affect anywhere from 5% to 66% of the population depending on the group studied, and they typically first appear during childhood or adolescence, most often between ages 10 and 19. The frequency tends to decrease as you get older.
Mouth Ulcers vs. Cold Sores
People often confuse mouth ulcers (canker sores) with cold sores (fever blisters), but they’re fundamentally different. Mouth ulcers appear inside the mouth and look like a single round sore with a white or yellow center. Their cause is unknown, and they are not contagious. Cold sores, on the other hand, show up on the outside of the mouth around the lips as a cluster of small, fluid-filled blisters. They’re caused by the herpes simplex virus (HSV-1) and can spread from person to person through close contact.
If your sore is inside your mouth, it’s almost certainly a canker sore. If it’s on or around your lips and started as a blister, it’s likely a cold sore.
What Causes Mouth Ulcers
The exact cause of most mouth ulcers remains unknown, which can be frustrating if you get them often. However, several well-established triggers make them more likely to appear:
- Minor injuries: Biting the inside of your cheek, brushing too hard, dental work, or irritation from braces can all set off an ulcer.
- Nutritional deficiencies: Low levels of vitamin B12, folate, or iron are frequently linked to recurring mouth ulcers. These nutrients support cell repair and healthy tissue regeneration, and when your body runs short, the lining of your mouth becomes more vulnerable to breakdown.
- Stress and fatigue: Many people notice ulcers appearing during periods of high stress or poor sleep.
- Hormonal changes: Some women experience ulcers tied to their menstrual cycle.
- Certain foods: Acidic or spicy foods, including citrus fruits, tomatoes, and chocolate, are common culprits.
- Underlying conditions: In some cases, frequent mouth ulcers are associated with conditions like celiac disease, inflammatory bowel disease, or immune system disorders.
Three Types of Mouth Ulcers
Not all mouth ulcers are identical. They fall into three categories based on size and behavior.
Minor Aphthous Ulcers
These are the most common type. They’re small (usually under a centimeter), oval-shaped, and heal within one to two weeks without leaving a scar. Most people who get mouth ulcers are dealing with this type.
Major Aphthous Ulcers
These are larger and deeper than minor ulcers, often with irregular edges. They can take several weeks to heal and sometimes leave scarring. They’re less common but significantly more painful and disruptive.
Herpetiform Ulcers
Despite the name, these have nothing to do with the herpes virus. They appear as clusters of tiny sores (sometimes dozens at a time) that can merge into one larger, irregular ulcer. They’re uncommon and tend to heal within a couple of weeks without scarring.
How to Manage the Pain
Most mouth ulcers don’t need medical treatment, but the discomfort can be significant enough that you want relief while waiting for them to heal. Over-the-counter products containing benzocaine (a numbing agent) can temporarily dull the pain. Antiseptic rinses containing hydrogen peroxide help keep the area clean and may reduce irritation. You can also make a simple rinse at home by dissolving half a teaspoon of salt in a cup of warm water and swishing gently.
Avoiding spicy, acidic, or crunchy foods while the ulcer is active makes a noticeable difference. Soft, cool foods are generally the easiest to tolerate. Drinking through a straw can help liquids bypass a painful spot on the inner lip or cheek.
For more severe or persistent ulcers, a doctor or dentist may prescribe a steroid-based mouth rinse to reduce inflammation, or a topical solution that chemically cauterizes the sore and can shorten healing time to about a week. Oral medications are reserved for severe cases that don’t respond to topical treatment.
Reducing How Often They Come Back
If you get mouth ulcers frequently, a few changes may help reduce the frequency. Getting enough B12, folate, and iron through your diet or supplements is a practical first step, especially if blood work confirms a deficiency. Foods rich in these nutrients include leafy greens, eggs, fortified cereals, red meat, and legumes.
Using a soft-bristled toothbrush and being gentle around the gums reduces the minor tissue injuries that can trigger ulcers. Some people wonder about switching to a toothpaste free of sodium lauryl sulfate (SLS), the foaming agent in most toothpastes. The evidence here is mixed. Some studies suggest that toothpastes without certain allergenic ingredients reduced ulcer frequency, but a 2019 review found there wasn’t enough data to confirm that SLS-free toothpastes consistently reduce how often ulcers occur, how long they last, or how much they hurt. It may be worth trying if you get frequent ulcers, but it’s not a guaranteed fix.
Managing stress, getting adequate sleep, and identifying personal food triggers through an elimination approach can also help. Keeping a simple log of when ulcers appear and what you ate or experienced in the days before can reveal patterns over time.
When a Mouth Ulcer Needs Attention
A mouth ulcer that lasts longer than three weeks warrants a visit to a healthcare provider. The same goes for ulcers that are unusually large, spreading, extremely painful, accompanied by a high fever, or recurring so frequently that new ones appear before old ones heal. In rare cases, a sore that doesn’t heal can be a sign of oral cancer, particularly in people who use tobacco or drink heavily. Persistent ulcers are usually still benign, but getting them checked rules out anything more serious.