Oral irritations and ulcerations occur frequently in the general population. Recurrent aphthous ulcers (RAU) are the most common. There are three types of RAU — minor, major and herpetiform, the most common being minor aphthae. The exact etiology of RAU is not known. Systemic and local factors, as well as infectious agents, have been proposed. Certain medications and foods are associated with oral ulcerations, and chemicals such as sodium lauryl sulfate (SLS) contained in dentifrices have also been implicated. RAU also occur in more serious systemic diseases and where appropriate patients should be referred for screening and medical care. Treatment of recurrent aphthous ulcers is palliative, based on the severity of the lesions. Both topical and systemic medications are available. Nutritional and oral hygiene advice should also be given, and if patients are sensitive to SLS, a low-dose SLS or SLS-free dentifrice should be recommended.