

Mouth ulcers occur in several forms. They can appear anywhere in the mouth, except for the hard palate and top of the tongue or lips. There are three main types of mouth ulcers:
Minor ulcer is the most common form of mouth ulcer, around 80% of all mouth ulcer cases. They commonly have a diameter between 2 and 8 millimetres and are not bigger than 10mm in size. Minor ulcers appear singly and heal naturally within 7 to 14 days.

Major ulcers are less common, 10% of the cases. Major ulcers have a diameter greater than 10mm and usually only one or two appear at a time. They are very painful and sensitive and may take anywhere between 10-30 days to heal and may leave a scar after they heal. Major ulcers are less common, around 10% of all mouth ulcers.

Herpetiform form as multiple, pinhead-sized sores. The number of ulcers can range from five to 100. These tiny ulcers often fuse together to form larger, irregular shaped sores, which are very painful. Around 5-10% of mouth ulcers are herpetiform. Herpetiform ulcers are not related to the herpes virus.

About 20% of the population suffers from chronic mouth ulcer, called recurrent oral ulceration or recurrent aphthous stomatisis. This disorder is characterized by recurring ulcers every week or month.