Mouth ulcers and cold sores are not the same thing, according to WebMD. Cold sores are caused by a virus, says Mayo Clinic, while regular mouth ulcers can have a variety of causes.
Mouth ulcers are sometimes a result of eating acidic foods such as citrus, notes WebMD. They are also caused by a person biting the inside of her cheek or a tooth or braces scraping against the inside of the mouth. Vitamin and mineral deficiencies also cause mouth ulcers.
Cold sores are tiny blisters that cluster around a person's mouth, says Mayo Clinic. They are contagious, filled with fluid and crust over after they break. They heal without a scar within two weeks to a month.