Mouth ulcers are common, painful and not well understood. Unlike other conditions affecting the cheeks, tongue and gums, mouth ulcers often occur in young and healthy people. Mouth ulcers are more common in some families, and some genetic factors appear to increase the risk of having mouth ulcers. This project aims to validate the findings from other studies, by checking whether these genetic risk factors also increase the risk of having mouth ulcers for participants in ALSPAC.