Aphthous ulcers are small blisters or sores in the mouth, usually three to four millimeters in diameter. They usually have a grayish-white or thick yellow color with a red inflamed border. Aphthous ulcers often appear on the inside of the lips, cheeks or under the tongue. They cause a stabbing pain, especially when eating acidic or hot foods. Some people can feel a aft coming by a recognizable aching sensation. Sometimes the oral mucosa is also red and irritated.

The exact cause of ulcers is not fully known, but they generally do not cause permanent damage to health. Some possible causes include:

• Accidentally biting the cheek while chewing
• Powerful brushing
• Badly fitting teeth or sharp teeth rubbing against the cheek
• Inadequate oral hygiene
• Infection with a virus or bacteria
• Conditions that make the mouth more susceptible to infection
• Reaction to certain medications