In addition, there is research that suggests canker sores may be caused by a faulty immune system that uses the body's defenses against disease to attack and destroy the normal cells of the mouth or tongue. British studies indicate that canker sores in about 20 percent of all patients are partially caused by nutritional deficiencies, especially a lack of vitamin B12, folic acid and iron. Similar studies performed in the United States, however, have not confirmed these findings. In a small percentage of patients canker sores occur in conjunction with gastrointestinal problems, such as an inability to digest certain cereals, and thus 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 only have bouts of canker sores during certain phases of their menstrual cycles.
The majority of women, in addition, experience improvement or remission of their canker sores during pregnancy. In clinical studies, researchers have also used hormone therapy to successfully treat some women. Both emotional stress and injury to the mouth, such as scratching by abrasive foods or a stray toothbrush bristle, can trigger outbreaks of canker sores although these factors probably do not cause the disorder. Women are more likely than men to have recurrent canker sores and professionals are more likely to have the disorder than nonprofessionals. Genetic studies indicate that susceptibility to recurrent outbreaks of canker sores is inherited in some patients, which partially explains the frequent tendency of the disorder to be shared by family members.