Women are more likely to have canker sores during their premenstrual period. Canker sores are sometimes confused with cold sores. Cold sores are caused by herpes simplex virus. This disease, also known as oral herpes or fever blisters, can occur anywhere on the body. Most commonly, herpes infection occurs on the outside of the lips and the gums, and much less frequently on the inside the mouth.
Cold sores are infectious.
The exact cause of canker sores is uncertain, however, they seem to be related to a localized immune reaction. Other proposed causes for this disease are trauma to the affected areas from toothbrush scrapes, stress, hormones, and food allergies. Canker sores tend to appear in response to stress. The initial symptom is a tingling or mildly painful itching sensation in the area where the sore will appear. After one to several days, a small red swelling appears.