Canker sores are small, round sores on the inside of the cheek, under the tongue, or in the back of the throat. They usually have a red edge and a gray center. They can be quite painful. They are not the same as cold sores, which are caused by herpes simplex.
Canker sores aren't contagious. They may happen if you have a viral infection. They may also be triggered by stress, food allergies, lack of vitamins and minerals, hormonal changes or menstrual periods. In some cases the cause is unknown.
In most cases, the sores go away by themselves. Some ointments, creams or rinses may help with the pain. Avoiding hot, spicy food while you have a canker sore also helps.