A mouth ulcer is a small, open sore that forms on the soft tissue inside your mouth, such as the inner cheeks, lips, tongue, or the floor of the mouth. Most are harmless, heal on their own within one to two weeks, and are surprisingly common. They’re also called canker sores, and while they can be painful enough to make eating and talking uncomfortable, they’re rarely a sign of anything serious.
What Mouth Ulcers Look and Feel Like
A typical mouth ulcer is round or oval with a white or yellow center and a red border. Most are small, less than 1 centimeter across, and shallow. You might get just one or several at the same time. The pain tends to be worst in the first few days, especially when food, drinks, or your teeth brush against the sore. Acidic or spicy foods can make the sting noticeably worse.
There are three types, categorized by size and number. Minor ulcers are the most common, staying small and healing without scarring. Major ulcers are larger, penetrate deeper into the tissue, and can leave a scar when they finally close. Herpetiform ulcers appear as clusters of many tiny sores that can merge together. Despite the name, herpetiform ulcers are not caused by the herpes virus.
Mouth Ulcers vs. Cold Sores
People often confuse mouth ulcers with cold sores, but they’re different in almost every way. The simplest distinction is location: mouth ulcers only form inside the mouth, while cold sores (fever blisters) appear on the outside, usually around the border of the lips. Cold sores look like patches of small fluid-filled blisters and are caused by herpes simplex virus type 1. Mouth ulcers have no known viral cause and are not contagious. You can’t pass a mouth ulcer to someone by sharing a drink or kissing.
Common Causes and Triggers
No single cause explains every mouth ulcer, but several well-established triggers account for most of them. Minor tissue injuries are one of the most frequent: biting your cheek, brushing too hard, or irritation from braces or a rough tooth edge. Stress and lack of sleep are also reliable triggers for many people.
Nutritional gaps play a role too. Low levels of vitamin B12, iron, and folate are linked to recurrent oral ulcers. Research comparing people with oral mucosal diseases to healthy controls has consistently found significantly lower B12 levels in those with mouth sores. If you get ulcers often, a simple blood test can check whether a deficiency is contributing.
Hormonal changes, particularly around menstruation, can trigger flare-ups in some people. Certain foods, especially citrus fruits, tomatoes, chocolate, and coffee, seem to provoke ulcers in susceptible individuals, though the specific triggers vary from person to person. Some toothpastes containing sodium lauryl sulfate, a foaming agent, have also been associated with more frequent ulcers.
Medications That Can Cause Mouth Ulcers
Several common medications can irritate the lining of your mouth. Nonsteroidal anti-inflammatory drugs like aspirin and naproxen are among the more frequent culprits, sometimes causing white or yellowish lesions and tissue sloughing inside the mouth. Certain blood pressure medications, including some angiotensin-receptor blockers, can produce similar effects. Placing crushed aspirin directly against a sore tooth or gum, a home remedy some people try, can cause a chemical burn on the tissue.
When Mouth Ulcers Signal Something Else
A mouth ulcer that heals within two weeks is almost always benign. But recurrent ulcers, ones that come back frequently over months or years, sometimes point to an underlying condition. Celiac disease, Crohn’s disease, and Behçet’s disease all include mouth ulcers among their symptoms. An immune system that’s suppressed by illness or medication can also lead to persistent or unusually severe sores.
The most important red flag is an ulcer that doesn’t heal. Any mouth sore lasting longer than three weeks should be evaluated by a doctor or dentist. Non-healing ulcers, unexplained lumps, and persistent lesions inside the mouth are among the early warning signs of oral cancer. These signs are difficult to distinguish from harmless sores through visual inspection alone, which is why professional evaluation matters. This is especially true for people who smoke, drink alcohol heavily, or have a history of HPV infection.
How to Manage the Pain at Home
Most mouth ulcers don’t need treatment beyond basic pain management while they heal. A saltwater rinse is the simplest option: dissolve about half a teaspoon of salt in a cup of warm water and swish gently. A baking soda rinse works similarly, using one teaspoon of baking soda in half a cup of warm water. Either rinse a few times a day can help keep the area clean and reduce irritation.
Over-the-counter gels and pastes containing benzocaine, a numbing agent, can temporarily relieve pain. These are applied directly to the ulcer and form a protective layer over the sore. Avoiding foods that aggravate the ulcer makes a real difference too. Stick to softer, cooler foods during the worst days, and try drinking through a straw if the ulcer is on your inner lip or cheek.
For people with frequent or particularly painful ulcers, a dentist or doctor may recommend a prescription-strength topical treatment. These are typically anti-inflammatory and can shorten healing time, especially for major ulcers that might otherwise take weeks to close and leave scarring.
Reducing How Often They Come Back
If you get mouth ulcers regularly, a few adjustments can lower the frequency. Switching to a toothpaste without sodium lauryl sulfate is a low-effort change that helps some people noticeably. Using a soft-bristled toothbrush reduces the minor tissue damage that can trigger a new sore. Keeping a food diary for a few weeks can help you identify personal triggers, since the foods that provoke ulcers vary widely between individuals.
Addressing nutritional deficiencies is one of the more effective long-term strategies. If blood work shows low B12, iron, or folate, correcting the deficiency through diet or supplements often reduces how frequently ulcers appear. Managing stress through sleep, exercise, or other means won’t eliminate ulcers entirely, but chronic stress is one of the most consistent triggers people report, and reducing it tends to help.