The exact cause of mouth ulcers is
unknown
In some cases they are thought to be
caused by an overreaction by the body's
own immune system.
Factors that appear to provoke them
include stress, fatigue, illness,
injury from accidental biting, hormonal
changes, menstruation, sudden weight
loss, food allergies and deficiencies
in vitamin B12, iron and folic acid.
Some drugs, such as nicorandil, have
been linked with mouth ulcers.
Trauma to the mouth is a common cause
of mouth ulcers. Physical trauma, such
as toothbrush abrasion, poking with
sharp food, accidental biting (this can
be particularly common with sharp
canine teeth), or dental braces can
cause mouth ulcers by breaking the
mucous membrane.
Other factors, such as chemical
irritants or a burn in the mouth, may
also lead to the development of ulcers.
However in many cases, the precise
cause is unknown.
A common cause of ulcers is gluten
intolerance, in which case consumption
of wheat, rye, or barley can result in
chronic mouth ulcers. If gluten
intolerance is the cause, prevention
means taking most breads, pastas,
cakes, pies, cookies, scones, biscuits,
beers etc. out of the diet and
substituting gluten-free varieties
where available.
Artificial sugars, such as those found
in diet cola and sugarless gum, have
been reported as causes of mouth ulcers
as well. They can also be linked to an
increased intake of acids such as
ascorbic acid (one form of Vitamin C)
or citric acid. In this case the sores
disappear after intake decreases (for
example, by substituting ascorbate
salts for ascorbic acid).
Repeat episodes of mouth ulcers can be
indicative of an immunodeficiency,
signalling low levels of immunoglobulin
in the mucous membrane of the
mouth.
Chemotherapy is a common cause of mouth
ulcers. Mouth ulcers may also be
symptoms or complications of several
diseases listed in the following
section.
A common urban myth is that mouth
ulcers are directly connected to the
onset of the herpes simplex virus, but
in reality ulcers associated with
herpes (or cold sores) are of an
entirely different nature from mouth
ulcers, which are not contagious.