Causes

The precise cause of canker sores remains unclear, though researchers suspect that a combination of factors contributes to outbreaks, even in the same person.

Possible triggers for canker sores include:

• A minor injury to your mouth from dental work, overzealous brushing, sports mishaps or an accidental cheek bite
• Toothpastes and mouth rinses containing sodium lauryl sulfate
• Food sensitivities, particularly to chocolate, coffee, strawberries, eggs, nuts, cheese, and spicy or acidic foods
• A diet lacking in vitamin B-12, zinc, folate (folic acid) or iron
• An allergic response to certain bacteria in your mouth
• Helicobacter pylori, the same bacteria that cause peptic ulcers
• Hormonal shifts during menstruation
• Emotional stress

Canker sores may also occur because of certain conditions and diseases, such as:

• Celiac disease, a serious intestinal disorder caused by a sensitivity to gluten, a protein found in most grains
• Inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis
• Behcet's disease, a rare disorder that causes inflammation throughout the body, including the mouth
• A faulty immune system that attacks healthy cells in your mouth instead of pathogens, such as viruses and bacteria
• HIV/AIDS, which suppresses the immune system

Unlike cold sores, canker sores are not associated with herpes virus infections.