Mouth ulcers are sores that appear in the mouth, often on the inside of the cheeks.
Mouth ulcers, also known as aphthous ulcers, can be painful when eating, drinking or brushing teeth.
Occasional mouth ulcers are usually harmless and clear up on their own. Seek medical advice if they last longer than 3 weeks or keep coming back.
Mouth ulcers cannot be caught from someone else.
Up to 1 in 5 people get recurrent mouth ulcers.