Cold sore

A cold sore is a fluid-filled blister that usually appears at the edge of thelips. Other names for a cold sore are fever blister, oral herpes, labial herpes, herpes labialis, and herpes febrilis. Cold sores do not usually form inside the mouth except for the very first time they occur, which distinguishesthem from the common canker sores.

Cold sores are caused by a herpes virus. There are eight different kinds of human herpes viruses. Only two of these, herpes simplex, types 1 and 2, can cause cold sores. It is commonly believed that herpes simplex virus type 1 infects above the waist and herpes simplex virus type 2 infects below the waist.This is not completely true. Both herpes virus type 1 and type 2 can cause herpes lesions on the lips or genitals, but recurrent cold sores are almost always type 1.

Oral herpes is very common. More than 60% of Americans have had a cold sore,and almost 25% of those infected experience recurrent outbreaks. Most peoplewho have had cold sores became infected before age 10. Anyone can become infected by herpes virus and once infected, the virus remains latent for life. Herpes viruses are spread from person to person by direct skin-to-skin contact.The highest risk for spreading the virus is the time period beginning with the appearance of blisters and ending with scab formation. However, infected persons need not have visible blisters to spread the infection to others, since the virus may be present in the saliva without obvious oral lesions.

Viruses are different from bacteria. While bacteria are independent and can reproduce on their own, viruses enter human cells and force them to make morevirus. The infected human cell is usually killed and releases thousands of new viruses. The cell death and resulting tissue damage cause the actual cold sores. In addition, herpes virus can infect a cell, and instead of making thecell produce new viruses, it hides inside the cell and waits. Herpes virus hides in the nervous system. This is called latency and may last days, months,or even years. At some future time, the virus "awakens" and causes the cell to produce thousands of new viruses, which sparks an active infection.

Active infections that follow periods of latency are called "recurrent" infections. Although it is unknown what triggers latent virus to activate, severalconditions seem to bring on infections. These include stress, illness, tiredness, exposure to sunlight, menstruation, fever, and diet.

While anyone can be infected by herpes virus, not everyone will show symptoms. The first symptoms of herpes occur within 2-20 days after contact with an infected person. Symptoms of the primary infection are usually more severe than those of recurrent infections. The primary infection can cause symptoms like other viral infections including tiredness, headache, fever, and swollen lymph nodes in the neck.

Typically, 50-80% of persons with oral herpes experience a prodrome (symptomsof oncoming disease) of pain, burning, itching, or tingling at the site where blisters will form. This prodromal stage may last anywhere from a few hours, to one to two days. The herpes infection prodrome occurs in both the primary infection and recurrent infections.

In 95% of the patients with cold sores, the blisters occur at the outer edgeof the lips which is called the "vermilion border." Less often, blisters formon the nose, chin, or cheek. Following the prodrome, the disease process israpid. First, small red bumps appear which quickly form fluid-filled blisters. The painful blisters may either burst and form a scab or dry up and form ascab. Within two days of the first red bumps, all the blisters have formed scabs. The skin heals completely and without scarring within six to ten days.

Some children have a very serious primary (first episode) herpes infection called "gingivostomatitis." This causes fever, swollen lymph glands, and numerous blisters inside the mouth, and on the lips and tongue which may form large, open sores. These painful sores may last up to three weeks and can make eating and drinking difficult. Because of this, young children with gingivostomatitis are at risk for dehydration.

Most people experience fewer than two recurrent outbreaks of cold sores eachyear. Some people never experience outbreaks, whereas some have very frequentoutbreaks. In most people, the blisters form in the same area each time andare triggered by the same factors (such as stress, sun exposure, etc.).

Because oral herpes is so common, it is diagnosed primarily by symptoms. Laboratory tests may be performed to confirm the diagnosis.

There is no cure for herpes virus infections. There are antiviral drugs available which have some effect in lessening the symptoms and decreasing the length of herpes outbreaks. There is evidence that some may also prevent future outbreaks. Acyclovir (Zovirax) is the drug of choice for herpes infection andcan be given intravenously or taken by mouth. It can be applied directly to sores as an ointment but is less effective in this form.

Oral herpes can be painful and embarrassing but it is not a serious infection. There is no cure for oral herpes, but outbreaks usually occur less frequently after age 35. The spread of herpes virus to the eyes is very serious. Herpes virus can infect the cells in the cornea and cause scarring which may impair vision.

The only way to prevent oral herpes is to avoid contact with infected persons. But because many people are not aware that they are infected, they can easily infect others. As of early 1998 there were no herpes vaccines available, although herpes vaccines are being tested. Good health and hygiene, in addition to minimizing contact with infected people, may help to reduce outbreaks ofcold sores and herpes.

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