Aphthous ulcer

Aphthous ulcers (aphthae) are a common type of mouth ulcer that appear on the mucous membrane. They are also known as aphthous stomatitis or canker sores.

Aphthous ulcers usually being as a round yellow spot, surrounded by a red halo, which breaks down into a punched-out ulcer which is covered by a white or greyish membrane.

There are three main types:

  • Minor aphthous ulcers – the most common variety. Usually <5 mm in diameter. They can be single or in clusters and do not usually cause much pain.
  • Major aphthous ulcers – less common. Generally >5 mm and can be singular or in a pair. These are more painful, especially when eating or drinking. They can last for weeks or months.
  • Herpetiform ulcers – these occur when multiple lesions fuse together to form large ulcers. Named for their similarity in appearance to herpes, although they are not caused by herpes simplex virus.


The cause of aphthous ulcers is unknown, but possible triggers include stress, minor injury to the oral mucosa (e.g. from ill-fitting braces or minor trauma from brushing or eating), nutritional deficiency, certain toothpastes (possibly related to the ingredient sodium laureth sulfate) and viral infections.

Aphthous ulcers are occasionally associated with systemic disease such as  Crohn’s disease, Behcet’s syndrome, coeliac disease and immune disorders.


There is no cure for an aphthous ulcer. Most will resolve within 1-2 weeks. Treatment to reduces discomfort can be useful and includes local anaesthetics, protective pastes and avoiding foods that trigger or exacerbate the ulcers.

Ulcers that do not heal within 3 weeks or where ulceration is severe and recurrent should prompt further investigation.