You can't see them and they pose no real risk to your health, but they kill. If you've ever suffered from canker sores (those small, round ulcers that develop on the lining of the cheeks and lips, the tongue, or the base of the gums), you know how they can make the simplest things—eating, drinking, brushing your teeth—a real pain.

"Canker sores are caused by an opportunistic virus that is always present in the mouth," explains Matthew Messina, D.D.S., consumer advisor for the American Dental Association. "The virus attacks when your resistance is down [due to stress, illness, or poor nutrition] or when a cut in the mouth gives it easy entry." There is no real cure for canker sores, but there are several steps you can take to help prevent them, make them less painful, and help them to heal faster.

Go easy. Since even the tiniest tear in your gums can quickly turn into a painful canker sore, be gentle with your toothbrush and take it easy when eating abrasive foods like potato chips.

Brush up on irritants. "Avoid caustic toothpastes and mouthwashes," advises Dr. Messina. Some studies have indicated that using toothpaste without sodium lauryl sulfate (SLS), a commonly used detergent, can reduce the occurrence of canker sores. "There is no confirmed evidence about SLS," says Dr. Messina, although he does recommend staying away from harsh, tartar-control toothpastes. If you want to try the SLS-free route, look for a natural product like Tom's of Maine or Rembrandt Whitening Toothpaste for Canker Sore Prevention.

Start supplementing. Although there isn't a lot of science to back it up, some people claim that taking the amino acid lysine or acidophilus (live cultures) daily helps prevent breakouts.

Eat right. Poor nutrition or eating too many acidic foods is a sure route to canker sores for some sufferers. If that describes you, eat ulcer-provoking foods like tomato sauce, orange juice, and salsa in moderation.

Dial a doc. For truly chronic canker sores, the best solution may be a trip to your doctor. There are two antiviral creams, Denavir and Zovirax, that can be applied to sores and often cut several days off the healing process. And Zovirax can also be taken in pill form to help permanently suppress the virus, but that means taking it every day whether you have an outbreak or not.

When all else fails, over-the-counter oral anesthetics like Orabase B or Anbesol can temporarily numb the pain. Though you may not grin, at least you might be able to bear it.