Recurrent aphthous stomatitis typically starts in childhood or adolescence with recurrent small, round, or ovoid ulcers with circumscribed margins, erythematous haloes, and yellow or grey floors.
Some cases have a familial and genetic basis, but most patients seem to be otherwise well.
However, a minority have aetiological factors that can be identified, including stress, trauma, stopping smoking, menstruation, and food allergy. The mouth ulcers in Behcet's syndrome are often major aphthae with frequent episodes and long duration to healing. In children aphthae also occur in periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis syndrome. This syndrome resolves spontaneously, and long term sequelae are rare. Diagnosis of aphthae is based on the patient's history and clinical features since specific tests are unavailable.