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Fever blisters and canker sores are two of the most common infections of the mouth, causing discomfort and annoyance to millions of Americans. The two disorders resemble each other and are often confused. Both disorders cause small sores to develop in the mouth that usually heal within two weeks. Canker sores differ from fever blisters, however, by not being preceded by a blister. Canker sores are also generally larger than fever blisters and several canker sores rarely merge to form one large sore, which happens with fever blisters. A final distinguishing trait between the two disorders is that canker sores usually occur on the movable parts of the mouth such as the tongue and the inside linings of the cheeks and lips, whereas fever blisters generally occur on the non-movable sections of the mouth such as the gums and the roof of the mouth, or on the outside of the lips and nostrils.
Fever Blister
About 100 million episodes of recurrent fever blisters occur yearly in the United States alone, with approximately 45 to 80 percent of all adults and children experiencing at least one bout with the blisters.
What Causes Fever Blisters?
Fever blisters are caused by a contagious virus called herpes simplex. There are 2 types of herpes simplex viruses: herpes simplex 1 or herpes simplex 2 (which is the virus that usually causes genital herpes).
Herpes simplex is highly contagious when fever blisters are present, and the virus is frequently transmitted by kissing. Children are often initially infected with herpes by contact with their parents, siblings, or other close relatives who have fever blisters. A child can also spread the virus by rubbing his or her cold sore and then touching other children. About 10 percent of oral herpes cases in adults are acquired by oral-genital sex with a person with active genital herpes.
Most people experience their first infection with herpes simplex 1 when they are less than 10 years of age. In these primary infections, the virus usually invades the moist membrane cells of the lips, mouth, or throat. The majority of people infected have no symptoms, but about 15 percent develop many fluid-filled blisters inside and outside the mouth three to five days after they are exposed to herpes simplex 1. The blisters may be accompanied by fever, swollen neck glands, and general aches. Fever blisters tend to merge and then collapse. Often a yellowish crust forms over the sores, which usually heal without scarring within 2 weeks.
The herpes virus, however, stays in the body. Once a person is infected with oral herpes, the virus remains in a nerve located near the cheekbone. The virus may stay permanently inactive in this site or occasionally may travel down the nerve to the skin surface where it causes a recurrence of fever blisters. Many people who experience recurring fever blisters feel itching, tingling or burning in the lip area 1 to 3 days before the fever blister occurs. Recurring blisters generally erupt at the outside edge of the lip or the edge of the nostril, and take almost as long to heal as the initial fever blisters. Recurrent attacks of fever blisters are normally less severe than primary attacks and the frequency of recurrence appears to decline after a person reaches age 35.
What Causes a Recurrence of Fever Blisters?
A number of factors weaken the body's defenses and trigger an outbreak of herpes simplex. These factors include emotional stress, fever, illness, injury, and overexposure to the sun. Many women experience recurrences during certain phases of their menstrual cycles. One study indicates that susceptibility to herpes recurrences is inherited. Research is currently underway to uncover how exactly "trigger" factors interact with the immune system and the virus to prompt a recurrence of fever blisters.
What Are the Treatments for Fever Blisters?
There currently is no cure for recurrent fever blisters. However, a number of medications can relieve some of the pain and discomfort associated with the sores, including numbing ointments applied to the blisters, antibiotics that control any occurring secondary infections, and ointments that soften the crusts of the sores.
Canker Sores
Recurrent canker sores are one of the most common inflammatory conditions of the mouth, afflicting about 20 percent of the general population. The medical terms for canker sores are aphthous stomatitis or aphthae.
Canker sores begin as small oval or round reddish swellings, usually on the movable parts of the mouth such as the tongue and the inside linings of the lips and cheeks. These swellings usually rupture within a day, are covered by a thin white or yellow membrane, and become edged by a red halo. The size of the sores varies from being an eighth of an inch wide in minor infections, to an inch and a quarter wide in more severe cases. Fever is rare and canker sores are rarely associated with other diseases. Usually a person will only experience a single or a few canker sores at a time. These sores generally heal within 2 weeks, though severe forms of the sores may leave scars.
Most people experience their first bout with canker sores when they are between the ages of 10 and 20 although children as young as 2 years of age may develop the condition. The frequency of canker sore recurrences varies considerably. Some people may only experience one or two episodes a year, whereas others may have a continuous series of canker sores. Most people experience tingling or pain in the area of the mouth where canker sores later develop.
What Causes Canker Sores?
It is not known what causes canker sores in all patients though more than one cause is likely even for individual patients. Attempts to find bacteria or viruses linked with the disease have not proven fruitful, though an allergy to a type of bacteria commonly found in the mouth may cause some people to develop canker sores. The sores might also be an allergic reaction to certain foods. In addition, there is research that suggests canker sores may be caused by a faulty immune system that uses the body's defenses to attack and destroy the normal cells of the mouth or tongue.
British studies indicate that canker sores in about 20 percent of all patients are partially caused by nutritional deficiencies, especially a lack of vitamin B12, folic acid and iron. Similar studies performed in the United States, however, have not confirmed these findings. In a small percentage of patients, canker sores occur in conjunction with gastrointestinal problems, such as an inability to digest certain cereals, and thus appear to be part of a generalized disorder of the digestive tract.
Female sex hormones may play a role in causing canker sores as well. Many women only have bouts of canker sores during certain phases of their menstrual cycles. In addition, the majority of women experience improvement or remission of their canker sores during pregnancy. Both emotional stress and injury to the mouth, such as scratching by abrasive foods or a stray toothbrush bristle, can also trigger outbreaks of canker sores, though these factors probably do not initially cause the disorder.
Who Is Susceptible?
Women are more likely than men to have recurrent canker sores and professionals are more likely to have the disorder than nonprofessionals. Genetic studies indicate that susceptibility to recurrent outbreaks of canker sores is inherited in some patients, which partially explains the frequent tendency of the disorder to be shared by family members.
What Is the Treatment?
Most doctors recommend that patients who have continual or frequently recurring bouts of canker sores undergo blood and allergy tests to determine if their sores are caused by a nutritional deficiency, an allergy, or some other correctable cause. Vitamin and other nutrient supplements often prevent recurrences or reduce the severity of canker sores in patients with a nutritional deficiency. Avoidance of foods allergies can also reduce canker sore recurrences.
There are a number of treatments that reduce the pain and duration of canker sores for patients whose outbreaks cannot be prevented. These treatments include numbing preparations, such as xylocaine, that are applied on the sores when a patient has only a few; and anti-inflammatory steroid mouthwashes or gels for patients with several sores. Mouthwashes containing the antibiotic tetracycline may reduce the unpleasant symptoms of canker sores and speed healing by preventing complicating bacterial infections in the sores. Clinical studies at the National Institute of Dental Research have shown that rinsing the mouth with tetracycline several times a day usually relieves pain in 24 hours and allows complete healing in 5 to 7 days. The U.S. Food and Drug Administration warns, however, that tetracycline administered to pregnant women and young children can permanently stain teeth. Steroid and tetracycline treatments both require a prescription and the care of a physician or dentist.
Patients with severe recurrent canker sores may need to take steroid or other immuno-suppressant drugs orally. These potent drugs may cause many undesirable side effects, however, and should be used only under the close supervision of a physician or dentist.
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