A mouth ulcer is small, round or oval and is about 10 mm in diameter. It is usually pale yellow in colour, but the surrounding areas may look red and swollen. A mouth ulcer can last for 5 to 7 days, and then disappear without leaving a scar.
1 Additional Answer
Mouth ulcers are round sores that line the inside of the mouth and affect the delicate tissue which is the mucous membrane. They often swell and are very tender, round or oval in shape and whitish in colour.