British studies show that in about 20 percent of patients, canker sores are partly nutritional deficiencies, especially lack of vitamin B12, folic acid and iron. Similar studies performed in the United States, however, have not confirmed such findings. In a small percentage of patients, canker sores occur with gastrointestinal problems, such as an inability to digest certain cereals. In these patients, canker sores appear to be part of a generalized disorder of the digestive tract. Female sex hormones apparently play a role in causing canker sores.
Many women have bouts of the sores during certain phases of their menstrual cycles.
Most women experience improvement or remission of their canker sores during pregnancy. Researches have used the hormone therapy successfully in clinical studies to treat some women. Both emotional stress and injury to the mouth can trigger outbreaks canker sores, but these factors probably do not cause the disorder. Women are more likely than men to have recurrent canker sores. Genetic studies show that susceptibility to recurrent outbreaks of the sores is inherited in some patients.