Aphthous ulcers What are aphthous ulcers? Aphthous ulcers (aphthae, or canker sores) are ulcers that form on the mucous membranes of the mouth or genitals. The most common type of an aphthous ulcer is recurrent minor aphthous ulcer (recurrent aphthous stomatitis). Recurrent aphthous ulceration is also be known as aphthous stomatitis. Aphthous ulcers are typically recurrent round or oval sores or ulcers that occur inside the mouth on areas where the skin is not tightly bound to the underlying bone (e.g. on the inside of the lips and cheeks or underneath the tongue). They may also appear on the genitals (Lipschutz ulcer), particularly if there is an associated condition such as Behcet disease or HIV . What causes aphthous ulcers? The exact reason why aphthous ulcers develop is not yet clearly defined. Current thinking is that the immune system has been disturbed by some external factor and this results in the development of aphthous ulcers. Also, approximately 40% of people who get ulcers have a family history of aphthous ulcers. Who is at risk of aphthous ulcers? Anyone can get aphthous ulcers; 20% of the population have them at least occasionally. They usually first appear in childhood or adolescence, and more commonly in females than males. Interestingly, smoking may be protective against aphthae, even though smoking makes many oral conditions worse. What are the signs and symptoms of aphthous ulcers? There are basically 3 types of aphthous ulcers: Recurrent minor aphthous ulcers, which occur in up to 80% of aphthous