About the only good thing about canker sores is, they're hidden inside the mouth. Beyond that—they're painful, annoying, and bound to erupt at the worst possible time. And common though they are, the medical world has mixed opinions on what causes them and what can prevent them from recurring. Canker sores, or mouth ulcers, are different from fever blisters, though they're often confused. They occur only inside the mouth and aren't [...]