Mouth ulcers are small, painful sores that form on the soft tissues inside your mouth, including the inner cheeks, lips, tongue, and floor of the mouth. Most heal on their own within 10 to 14 days and are not dangerous, though they can make eating, drinking, and talking uncomfortable. They’re extremely common, and nearly everyone will experience at least one at some point.
What They Look and Feel Like
A typical mouth ulcer is round or oval, less than 5 mm across, with a yellowish or grey-white center and a red ring around it. You might notice a tingling or burning sensation a day or two before the sore actually appears. Once it forms, the pain tends to be worst in the first few days and gradually fades as the ulcer heals.
They usually show up on soft, flexible surfaces: the inside of the cheeks and lips, the underside or edges of the tongue, and the floor of the mouth. You might get a single ulcer or a small cluster of up to five or six at once. Eating salty, spicy, or acidic foods tends to sting the most.
Three Types of Mouth Ulcers
Not all mouth ulcers behave the same way. They fall into three categories based on size, number, and severity.
Minor Ulcers
About 80% of people who get recurring mouth ulcers have this type. The sores are small (under 5 mm), appear in groups of one to six, and heal within two weeks without leaving a scar. They tend to come back every one to four months.
Major Ulcers
These affect roughly 10% of people with recurring ulcers. They’re larger, over 10 mm across, and can last five to ten weeks. Major ulcers can appear anywhere in the mouth, including the back of the throat, and they sometimes leave scars. Unlike minor ulcers, they don’t follow a predictable cycle.
Herpetiform Ulcers
The rarest type, affecting 1% to 10% of people with recurring ulcers. Despite the name, these have no connection to the herpes virus. They’re called “herpetiform” because the cluster pattern resembles a herpes outbreak. You can get up to 100 tiny ulcers at once, each about 2 to 3 mm wide, mostly on the tongue and floor of the mouth. They last one to two weeks individually, but the small sores sometimes merge into larger, irregular ulcers that can scar. This type is more common in older women.
Common Causes and Triggers
There’s no single, definitive cause for most mouth ulcers. Instead, a combination of triggers tends to set them off. The most widely recognized include:
- Physical trauma: biting the inside of your cheek, brushing too hard, or irritation from braces or sharp tooth edges
- Stress: emotional or physical stress is one of the most consistently reported triggers
- Food sensitivities: coffee, chocolate, cheese, nuts, and citrus fruits are common culprits
- Nutritional deficiencies: low levels of vitamin B12, iron, and folate are linked to recurrent ulcers
- Weakened immune function: your body’s ability to repair the mouth lining depends on a healthy immune response
- Certain medications: some drugs can trigger ulcers as a side effect
Vitamin B12 deficiency deserves special attention because it can cause a range of mouth problems beyond ulcers, including a burning or tingling tongue, cracked lips, and changes in taste. If you’re getting ulcers frequently and also feel fatigued or notice numbness in your hands and feet, a B12 deficiency could be a factor worth checking with a blood test.
When Ulcers Signal Something Else
Occasional mouth ulcers are rarely a sign of a deeper health problem. Frequent or unusually severe ulcers, however, can be associated with certain systemic conditions. In Behçet’s syndrome, an inflammatory disorder, recurrent oral ulcers appear in virtually 100% of patients and are a core part of the diagnosis, alongside genital ulcers, eye inflammation, and skin lesions. Mouth ulcers also occasionally appear in people with Crohn’s disease, though this is far less common, occurring in fewer than 10% of patients.
The most important red flag is a single ulcer that does not heal. A mouth sore lasting longer than three weeks should be evaluated by a doctor or dentist, as a non-healing ulcer is one of the recognized symptoms of oral cancer. This doesn’t mean every stubborn sore is cancerous, but the three-week mark is the threshold where professional evaluation is warranted.
How Mouth Ulcers Are Treated
Most mouth ulcers don’t need treatment at all. They resolve on their own within about two weeks. To manage pain in the meantime, over-the-counter gels and rinses designed for mouth sores can numb the area and create a protective barrier over the ulcer.
For ulcers that are particularly painful or large, a doctor or dentist may prescribe a steroid paste that you apply directly to the sore. This reduces inflammation and speeds healing. Severe or persistent cases sometimes require stronger prescription formulations held against the ulcer with gauze. The goal of these treatments is to shorten the duration of each outbreak and reduce pain, not to prevent future ulcers entirely.
Reducing How Often They Come Back
One of the more practical things you can do is switch to a toothpaste that doesn’t contain sodium lauryl sulfate (SLS), the foaming agent in most toothpastes. A systematic review of clinical trials found that people who used SLS-free toothpaste had fewer ulcers, shorter episodes, and less pain compared to when they used standard toothpaste. The effect was consistent across all four measures of ulcer activity that researchers tracked. SLS-free options are widely available at most pharmacies and grocery stores.
Beyond toothpaste, a few other strategies can help. Avoiding your known food triggers, whether that’s citrus, nuts, or chocolate, reduces the frequency of outbreaks for many people. Managing stress through whatever works for you, whether exercise, sleep, or simply reducing your workload during high-pressure periods, also makes a difference. If you suspect a nutritional deficiency, getting your levels of B12, iron, and folate checked gives you a concrete target to address through diet or supplements.
Using a soft-bristled toothbrush and being careful not to bite the inside of your cheeks or lips while eating can prevent the minor trauma that kick-starts many ulcers. If dental hardware like braces or a rough filling is causing repeated irritation in the same spot, your dentist can smooth the surface or apply protective wax.