When people get these painful little lesions, they want to know “why me?” and “what causes canker sores?” While it is only natural to ask these questions, they are somewhat hard to answer because doctors do not really know why canker sores occur. Fortunately there are several risk factors that have been identified that increase a person’s risk for developing these ulcers of the mouth.

Injury or trauma

Canker sores occur in sites where the mouth was injured. Often a person with canker sores can recall injuring the site that later gave rise to the lesion. For example, it is fairly common for an aphthous ulcer to occur in a place where a person accidently bit the tongue or inside of the cheek. Trauma from teeth is not the only insult that may lead to ulcers of the mouth—toothbrushes, sharp food, dining utensils, toothpicks, and any other object that can injure the mouth may serve as a focus for this type of mouth lesion.

Stress

On average, people that are more prone to depression and anxiety disorders are more commonly affected by canker sores. The link is strong enough that people have fewer canker sores when their depression and anxiety symptoms are effectively treated. However, mental and emotional stresses are not the only forms of stress that make a person susceptible to aphthous ulcers. Patients that endure great physical stress, such as from a serious or protracted illness, are more likely to develop canker sores than those without these stresses.

Food allergies

Certain food “allergies” or food sensitivities have been implicated in the development of cankers sores. While not every food will bring about cankers sores in every person, notable foods include:

• Cheese
• Chocolate
• Citrus fruits
• Coffee
• Cow’s milk
• Figs
• Gluten
• Nuts
• Potatoes

Heredity and genetics

It is common for canker sores to run in families. The degree to which the risk of developing canker sores is transmitted from one generation to the next is not known. However if one parent has had cankers sores, children have about a four in ten chance of having them as well. If both parents are afflicted, the child’s risk is about 90%.  This may have something to do with inherited features of immune system cells.

Fluctuations in hormones

The development of canker sores may be influenced by hormones, particularly female sex hormones such as estrogen and progesterone. Women are more likely to develop canker sores than men. Moreover, the times in which women are mostly likely to get aphthous ulcers correlates with certain points in the cycle. For instance, ovulation and just prior to menstruation are often when women experience the first signs of a new canker sore. Alternatively, some women experience a period free from canker sores during pregnancy.

Medical health issues

Certain systemic and gastrointestinal illnesses are associated with canker sores. One of the clinical manifestations of Crohn’s disease, ulcerative colitis, or celiac disease may be canker sores. Recurrent and sometimes severe aphthous ulcers may occur in patients with Behçet’s disease, HIV/AIDS, neutropenia, or reactive arthritis (formerly called Reiter syndrome).

Exposure to chemicals

Nitrates, sodium lauryl sulfate, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the risk of canker sores in some people. Nitrates are found in treated, unpurified drinking water but are also used to preserve certain foods. Sodium lauryl sulfate is a mild detergent that is used in most toothpastes and other household products.

Smoking tobacco products

Note that what you are about to read in this section is not a recommendation to start smoking; however cigarette smoke may protect against canker sores. To be sure, smoking causes a number of horrible and deadly diseases that are far worse than canker sores. Nonetheless, tobacco smoking actually lowers the risk of aphthous ulcers. Nonsmokers have much higher rates of canker sores than cigarette smokers. In fact, smokers that quit smoking notice an increase in the number of sores after they stop. Ironically, poor oral hygiene has been linked to the development of canker sores, independent of smoking.

Infection

A number of viruses and bacteria have been associated with canker sores; however it is important to note that none are believed to be a direct cause of the disease. In other words, being infected with a certain virus may increase a person’s susceptibility to getting aphthous ulcers of the mouth though many people with these same viruses do not get canker sores. Because of this connection, some patients fear that canker sores are contagious. In actuality, canker sores are not contagious.

References

Scully C, Gorsky M, Lozada-Nur F. The diagnosis and management of recurrent aphthous stomatitis: a consensus approach. J Am Dent Assoc 2003;134:200-207.

Shohat-Zabarski R, Kalderon S, Klein T, Weinberger A. Close association of HLA-B51 in persons with recurrent aphthous stomatitis. Oral Surg Oral Med Oral Pathol 1992;74:455-458.