Also known as aphthous ulcers, canker sores are small, shallow open wounds that usually appear on the inside of the cheeks or lips, but can also sometimes affect the back of the throat and tonsils. They are also known to be the most common type of mouth ulcer. A canker sore is usually characterized by a white or yellow open wound that is surrounded by red, inflamed soft tissue.
Unlike cold cores, canker sores only appear inside of the mouth and are not contagious. They can be painful, however, and can make eating and talking difficult. Most canker sores go away on their own in a week or two. Stress, mouth injury from vigorous tooth brushing, dental work, braces or dentures, highly acidic foods, toothpaste containing sodium lauryl sulphate or deficiency in vitamins B12, zinc, folate (folic acid), or iron are some of the factors that can contribute to the development of canker sores.