[1] It refers to any inflammatory process affecting the mucous membranes of the mouth and lips, with or without oral ulceration.

Lack of iron can cause genetic downregulation of these elements, leading to ineffective repair and regeneration of epithelial cells, especially in the mouth and lips.

[3]: 49 Aphthous stomatitis (canker sores) is the recurrent appearance of mouth ulcers in otherwise healthy individuals.

The cause is not completely understood, but it is thought that the condition represents a T cell mediated immune response which is triggered by a variety of factors.

Aphthous stomatitis is one of the most common diseases of the oral mucosa, and is thought to affect about 20% of the general population to some degree.

[4] The symptoms range from a minor nuisance to being disabling in their impact on eating, swallowing, and talking, and the severe forms can cause people to lose weight.

There is no cure for aphthous stomatitis,[5] and therapies are aimed at alleviating the pain, reducing the inflammation and promoting healing of the ulcers, but there is little evidence of efficacy for any treatment that has been used.

This causes skin folds around the angle of the mouth which are kept moist by saliva, which in turn favours infection; mostly by Candida albicans or similar species.

[7] The oral mucosa is also more vascular (has a better blood supply) than skin, meaning that any antigens are more quickly removed from the area by the circulation.

[7] Allergic contact stomatitis appears as non-specific inflammation, so it may be mistaken for chronic physical irritation.

[7] Allergens that may cause allergic contact stomatitis in some individuals include cinnamaldehyde, Balsam of Peru, peppermint, mercury, gold, pyrophosphates, zinc citrate, free acrylic monomer, nickel, fluoride, and sodium lauryl sulfate.

Geographic tongue is so named because there are atrophic, erythematous areas of depapillation that migrate over time, giving a map-like appearance.