The more acidic foods can cause mouth ulcers. Oranges, lemons and other citrus fruits contain citric acid.
Milk and dairy products contain lactic acid. People who are lactose intolerant or have milk allergies may have recurring mouth ulcers, as well as the digestive problems commonly associated with consumption of dairy products.
The alpha and beta hydroxy acids are found in most fruits and vegetables. But, usually the concentration is too low to cause a problem.
Salicylic acid is found in aspirin. Chewing aspirin is more likely to cause a mouth ulcer than swallowing the tablet whole.
A mouth ulcer could be a symptom of a food allergy. Doctors refer to it as oral allergy syndrome. Other symptoms include burning and itching of the lips.
Various nutritional deficiencies are accompanied by mouth ulcers. The lack of essential nutrients causes the mucus membrane lining to become thinner and more easily damaged.
Anemia or a lack of iron in the diet can cause the sores. Other symptoms of iron deficiency include hair loss, weakness and brittle fingernails.
A folate deficiency could be the cause, especially if there has been a loss of appetite and sudden weight loss. Sudden weight loss is sometimes referred to as one of the causes. The nutritional deficiency could have come first or be a result of excessive dieting.
People with anorexia nervosa and bulimia often have sores in their mouths. Frequent vomiting can cause or contribute to the sores, because stomach acid burns the lining of the mouth.
Often the canker sores can result after injuries. A tooth brush or a sharp food can cause a tiny tear in the lining. Sometimes people are not aware of the injury at the time. It is just enough of a tear to cause the ulcer to form.
Biting the inside of the lip or cheek can cause ulcers. This may occur during the night while a person is sleeping. Once again, they are unaware of the injury.
Some brands of toothpaste contain known irritants. Sodium laurel sulfate is an example. Several studies have linked the chemical to mouth ulcer formation.
There are other chronic sores including celiac disease, stomatitis and Sutton's Disease. Those are less common. If you have a mouth ulcer, chances are it was caused by eating an acidic food or a slight injury.