It may start with a tingle on the inside of your lip. Or maybe a bit of a burning sensation on your inner cheek. You might wonder, did you poke yourself with a pointy end of a potato chip again? Or worse, who have you been kissing?
There's more than one type of sore that can develop inside your mouth. Some appear as flat lesions or shallow abrasions, while others may be raised bumps. They may be red, white, yellow or gray.
Aphthous ulcers (or aphthae), commonly known as canker sores, are small sores that develop in the soft tissues inside the mouth: the inside of the lips, the inner cheeks and on the tongue. These are the most common type of mouth ulcer.
There are three types of aphthous ulcers: minor ulcers, major ulcers and herpetiform ulcers. Chances are good that if you find yourself with a mouth ulcer it will be a minor aphthous type -- minor ulcers account for at least 80 percent of all aphthae, while major and herpetiform ulcers make up the remaining 20 percent [source: Cleveland Clinic].
Minor sores are usually less than 5 millimeters in diameter (although they can be anywhere from 1 to 10 millimeters and still be considered minor). Often, people develop their first minor ulceration as a child, teen or young adult. Major ulcerations, which affect adults, are similar to minor sores but are larger than one-half inch (1.3 centimeters) in diameter; and the rarest form, herpetiform ulcerations, are clusters of very small ulcers that usually affect only older adults. While some people will have just one or two ulcers in a lifetime, others -- at least one out of five people -- have chronic ulcerations, a condition called recurrent aphthous ulcers (RAU).
While canker sores are not contagious, another type of mouth sore is: the cold sore. Cold sores are sores that appear on the outside of the mouth. They're caused by a virus -- the herpes simplex virus -- and are so contagious that during ancient Roman times an outbreak of cold sores led Emperor Tiberius to ban kissing during public ceremonies.
But it's not the herpes simplex virus that causes ulcers inside the mouth. Let's find out what does, and if you're at risk.