About 40 percent of the U.S. population gets “canker sores,” which should not be confused with “cold sores” caused by the herpes simplex type 1 virus. Unlike cold sores, which occur primarily outside the mouth, canker sores occur inside the mouth. They are also quite painful and have no apparent cause, although they have been linked to nutritional problems such as a vitamin B12, zinc, folic acid, or iron deficiency. These potential triggers led researchers to see if taking a daily multi-vitamin would help prevent the occurrence of this common ailment. However, after one year, it was found that taking a daily multivitamin consisting of 100 percent of the recommended daily intake of essential vitamins had no effect. 

Canker sores, which appear as pale yellow ulcerations with a red ring, are not contagious. They can be triggered by stress and typically last ten days without treatment.