A canker sore is a common form of ulcer or open sore. An ulcer can be on an external surface like the mouth or an internal surface, like the stomach. They are caused by a break in skin or mucus membrane that won't heal.
Ulcer comes from the Greek elkos meaning "wound." An ulcer is a wound or lesion that is inflamed and painful. Ulcers are commonly found in the stomach where they are called peptic ulcers. They are caused by a bacteria in the intestinal tract or an overuse of drugs that disturbs the lining of the digestive tract. An ulcer is very acidic and painful. I hope you don't get one.
