By: J. Shahangian, DDS, MS- San Diego Board Certified Pediatric Dentist
Canker Sores/Cold Sores
There is difference between cold sores and canker sores (also known as RAU, or aphthous ulcers). Unlike cold sores that grow outside of the mouth (usually on the lip), canker sores grow inside of the mouth.
Canker sores are tiny ulcers or sores in the mouth that have a red borer and a white or gray base in the middle. Although their cause is unknown, they occur often.
Cold sores, which are also known as fever blisters, are caused by a virus know as the “herpes complex”. This viral infection is made up of clusters of painful blisters that are fluid. These blisters are commonly found around the lips, and in some rare occasions, under the chin and nose. These highly contagious blisters are caused by type 1 herpes virus.
Like all ulcers, canker sores are difficult to treat. Once they appear, there is no proven medicine that can help eliminate or hasten recovery time. However, there are many medicines that can help alleviate the some of the symptoms. For example, you can use topical anesthetics that are over the counter. Canker sores may last up to one or two weeks.
On the other hand, cold sores can usually last for one week. Since cold sores are vial, you can take medicine for viral infection and also, over the counter anesthetics.
 http://www.sunnysidedentistryforchildren.com/library/2029/CankerSores%2FColdSores.html, accessed January 2, 2012