Canker Sores usually show up on soft parts of the mouth where there is no bone underneath, like the tongue or cheeks.
If the lesion is on your palate or your gums, it is not a canker sore and you should have the sore evaluated by your dentist.
Canker sores happen most often because of irritation to the mouth. Stress, acidic foods like oranges, vinegar or tomatoes, aggressive toothbrushing, rough edges of foods like nuts or chips can also cause canker sores.
Canker sores are not caused by an infection from bacterior or viruses.
The best way to get relief from these sores is to do a "liquid swish" using a mixture of water and baking soda or salt. Salt water may sting but has been documented to speed up the healing process.
These sores usually only last one to two weeks. If the lesion lingers after two weeks, I recommend you see your dentist.