The Encyclopedia of Natural Medicine, 3rd Ed.

Canker Sores


• Single or clustered shallow, painful ulcers found anywhere in the oral cavity

• Ulcerations usually resolve in 7 to 21 days but are recurrent in many people

Canker sores (the medical term is aphthous stomatitis) are quite common, but in 20% of the U.S. population they tend to recur often (in which case they are called recurrent aphthous ulcers, or RAU). Although the lesions generally heal on their own, some individuals seem to have canker sores all the time.


Local chemical or physical trauma often initiates ulcers in susceptible individuals. Stress is frequently a precipitating factor in RAU, suggesting a breakdown in normal host protective factors.1 Allergies, gluten sensitivity, and nutrient deficiency are also common causes. One controlled study has shown a statistically significant increase in RAU in subjects taking nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen.2


Allergies, particularly food allergies to milk and gluten, are a common cause. The oral cavity is obviously the first site of contact for ingested allergens and many inhaled ones. The lesions and the association of RAU with increased serum antibodies to food antigens strongly suggest that an allergic reaction is involved.3 Furthermore, the presence of higher levels of allergic antibodies (IgE) and white blood cells associated with allergies (mast cells and basophils) are characteristic of RAU.4,5 Mast cells and basophils contain granules of histamine and other allergic mediators that are released in response to allergens. The sensitivity is not necessarily to a food; it can also be to a food additive or contact metal. Frequent nonfood allergens inducing RAU include:6

Benzoic acid





Sorbic acid

Gluten Sensitivity

Considerable evidence indicates that sensitivity to gluten is associated with RAU. The incidence of RAU is increased in patients with celiac disease (see the chapter “Celiac Disease”).711 Withdrawing gluten from the diet results in complete remission of RAU in patients with celiac disease and some improvement in others.711

Nutrient Deficiency

The oral cavity is often the first place that nutritional deficiency becomes visible because of the high turnover rate of the cells that line it (the mucosal epithelium). Although a number of nutrient deficiencies can lead to canker sores, thiamine deficiency appears to be the most significant. In one study seeking to examine whether thiamine deficiency is associated with RAU, levels of transketolase (a thiamine-dependent enzyme) were determined in 70 patients with RAU and 50 patients from a control group.12 Low levels of transketolase were found in 49 of 70 patients with RAU, compared with only 2 of 50 among the controls.

Several other studies show that nutrient deficiencies are much more common in RAU sufferers than others. For example, a study of 330 patients with RAU found that 47 (14.2%) were deficient in iron, folate, vitamin B12, or a combination of these nutrients.13 In another study of 60 patients, 28.2% were deficient in thiamine, riboflavin, or pyridoxine.14

Low nutrient status may explain why patients with RAU have an impaired antioxidant defense system, leading to higher levels of free radicals and damaged fats in the blood.15

Therapeutic Considerations

For RAU, the most effective treatments involve identifying the cause. Food allergies, gluten sensitivity, and nutrient deficiency should all be addressed and corrected. Correction of the cause will stop the cycle of RAU. For example, an allergy elimination diet has been shown to have good therapeutic results;16,17 elimination of gluten is curative in those with gluten sensitivity; and when nutrient deficiencies are corrected, most RAU patients have a complete remission.18 Even taking extra vitamin B12 (1,000 mcg per day) alone has shown benefit regardless of whether deficiency exists or not.19

Zinc supplementation has also been shown to be helpful. In one double-blind study, 40 patients with RAU were given either zinc sulfate (220 mg, providing 50 mg elemental zinc) or a placebo once per day for one month.20Results showed that the levels of serum zinc before treatment were below normal in 42.5% of the patients with RAU. After one month of zinc therapy, the sores were reduced and did not reappear for three months.

A small study of adolescents showed a reduction in the incidence of RAU and associated pain from 2,000 mg per day of vitamin C.21



• Recurrent canker sores can be caused by trauma, food sensitivities (especially milk and gluten sensitivities), stress, and/or nutrient deficiency.

• Eliminating food allergens, sources of gluten, and nutritional deficiencies results in a complete cure in most cases.

• Deglycyrrhizinated licorice (DGL) may be effective in promoting the healing of RAU.

Deglycyrrhizinated licorice (DGL) may be effective in promoting the healing of RAU. In one study, 20 patients were instructed to use a solution of DGL as a mouthwash (200 mg powdered DGL dissolved in 200 ml of warm water) four times per day.22 Of the 20 patients, 15 (75%) experienced 50 to 75% improvement within one day, followed by complete healing of the ulcers by the third day. DGL in tablet form may be more convenient and effective. For more information on DGL, see the chapter “Peptic Ulcer.”



Food allergies, gluten sensitivity, and nutrient deficiency should all be addressed and corrected. Considerable evidence suggests that gluten sensitivity may be a contributing factor in some patients.


The diet should be free of known allergens and, if gluten sensitivity is present, all gluten sources. Otherwise, the guidelines in the chapter “A Health-Promoting Diet” are appropriate.

Nutritional Supplements

• A high-potency multiple vitamin and mineral formula as described in the chapter “Supplementary Measures”

• Key individual nutrients:

  images Thiamine (vitamin B1): 50 to 100 mg per day

  images Vitamin B6: 25 to 50 mg per day

  images Folic acid: 400 to 800 mcg per day

  images Vitamin B12 (methylcobalamin): 1,000 mcg per day

  images Vitamin C: 500 to 1,000 mg twice per day

  images Zinc: 20 to 30 mg per day

• Fish oils: 1,000 mg EPA + DHA per day

• One of the following:

  images Grape seed extract (>95% procyanidolic oligomers): 100 to 300 mg per day

  images Pine bark extract (>95% procyanidolic oligomers): 100 to 300 mg per day

  images Some other flavonoid-rich extract with a similar flavonoid content, super greens formula, or another plant-based antioxidant that can provide an oxygen radical absorption capacity (ORAC) of 3,000 to 6,000 units or higher per day

Botanical Medicines

• DGL: one to two 380-mg chewable tablets 20 minutes before meals