Female sex hormones apparently play a role in causing canker sores. Many women have bouts of the sores only during certain phases of their menstrual cycles. Most women experience improvement or remission of their canker sores during pregnancy. Researchers have used hormone therapy successfully in clinical studies to treat some women. Both emotional stress and injury to the mouth can trigger outbreaks of 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. This partially explains why the disorder is often shared by family members. Most doctors recommend that patients who have frequent bouts of canker sores undergo blood and allergy tests to determine if their sores are caused by a nutritional deficiency, an allergy or some other preventable cause. Vitamins and other nutritional supplements often prevent recurrences or reduce the severity of canker sores in patients with a nutritional deficiency. Patients with food allergies can reduce the frequency of canker sores by avoiding those foods.