Lorraine is 25 years old and presents with a 1 week history of sore mouth ulcers. This is the first time she has had ulcers and over the counter treatments have been little relief. On examination, you observe two 4mm round ulcers on her inner left cheek. You explain these are minor aphthous ulcers and discuss the diagnosis further.
Which one of the following statements about aphthous ulcers is least correct?