Most mouth sores are nothing to worry about, and minor mouth ulcers will heal on their own in about seven to 10 days (it usually takes the major or herpetiform ulcers a little longer to heal, one month to several weeks).
While rare, some complications may occur. Mouth ulcers often cause pain, especially when eating, drinking and talking, and people who suffer from major recurrent aphthous ulcers have a risk of becoming dehydrated or undernourished if the pain from the large sores is severe enough to cause them to avoid food and beverages. These ulcers may also leave behind scars. Any sore that doesn't heal after two to three weeks should be looked at by a health care professional to rule out underlying conditions such as cancer, a viral or bacterial infection or a systemic disease.
There is no cure for mouth ulcers, but there are treatments aimed at relieving pain and swelling and that may encourage healing. Over-the-counter remedies such as anesthetic gels, liquid antacids and antihistamines often work well to reduce pain when applied directly to the ulcer. A health care professional may prescribe a stronger topical analgesic or corticosteroids to help relieve more severe pain.
There's also no way to prevent getting a mouth ulcer, although there are some tricks that may help to reduce the number of ulcerations and their severity.
Avoiding foods that are hot, spicy or acidic may help to reduce irritation in the mouth, a contributor to mouth ulcers, and good daily oral hygiene habits are also considered helpful in reducing ulcerations. Make note, though, that some studies recommend avoiding products that contain sodium lauryl sulfate, a common ingredient in toothpastes and mouthwashes, because it may cause damage to the soft tissue inside the mouth.
Sometimes, as is the case for people with celiac disease or those with certain food allergies (such as dairy), dietary changes may help reduce the occurrence of canker sores. Taking vitamin and mineral supplements, especially vitamin B12, iron and zinc may offer some protection against ulcer recurrence, as well.