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By Craig R. Pringle, BSc, PhD, Professor Emeritus, School of Life Sciences, University of Warwick

Chickenpox (varicella) is a highly contagious infection with the varicella-zoster virus that causes a characteristic itchy rash, consisting of small, raised, blistered, or crusted spots.

  • Chickenpox most often affects children, but the vaccine has greatly decreased the number of cases.

  • Before the rash appears, children have a mild headache, moderate fever, loss of appetite, and a general feeling of illness.

  • The diagnosis is based on symptoms, particularly the rash.

  • Most children recover completely, although some children get very sick and can even die.

  • Routine vaccination can prevent chickenpox.

  • Usually, only the symptoms need to be treated.

Chickenpox is an infection that mostly affects children. Before the introduction of a vaccine in 1995, about 90% of children developed chickenpox by age 15. Now, the use of the vaccine has decreased the number of cases of chickenpox per year by about 70%. However, in some countries, the vaccine is not available or is not included as a routinely recommended childhood vaccine.

The disease is spread by airborne droplets of moisture containing the varicella-zoster virus, which is a herpesvirus (see Herpesvirus Infection Overview). A person with chickenpox is most contagious just after symptoms start but remains contagious until the last blisters have crusted.

In children with a normal immune system, chickenpox is rarely severe. Most people with chickenpox simply have sores on the skin and in the mouth. However, the virus sometimes infects the lungs, brain, heart, liver, or joints. Such serious infections are more common among newborns, adults, and people with a weakened immune system (such as those who have HIV infection or who are taking drugs that suppress the immune system or high doses of corticosteroids).

A person who has had chickenpox develops immunity and cannot contract it again. However, the varicella-zoster virus remains dormant in the body after an initial infection with chickenpox, sometimes reactivating in later life, causing shingles (see Shingles). A shingles vaccine is available for older adults. This vaccine may decrease the risk of developing shingles in later life.


Symptoms begin 10 to 21 days after infection. They include

  • Mild headache

  • Moderate fever

  • Loss of appetite

  • A general feeling of illness (malaise)

Younger children often do not have these symptoms, but symptoms are often severe in adults.

About 24 to 36 hours after the first symptoms begin, a rash of small, flat, red spots appears. The spots usually begin on the trunk and face, later appearing on the arms and legs. Some children have only a few spots. Others have them almost everywhere, including on the scalp and inside the mouth.

Within 6 to 8 hours, each spot becomes raised; forms an itchy, round, fluid-filled blister against a red background; and finally crusts. Spots continue to develop and crust for several days. The spots may become infected by bacteria, causing skin infection with redness (cellulitis—see Cellulitis) or blisters (bullous impetigo—see Impetigo and Ecthyma) or, rarely, infection of the tissues under the skin.

New spots usually stop appearing by the fifth day, the majority are crusted by the sixth day, and most disappear in fewer than 20 days.

Sometimes children who have been vaccinated develop chickenpox. In these children, the rash is typically milder, fever is less common, and the illness is shorter. However, contact with the sores can spread the infection.

Spots in the mouth quickly rupture and form raw sores (ulcers), which often make swallowing painful. Raw sores may also occur on the eyelids and in the upper airways, rectum, and vagina. Spots in the voice box (larynx) and upper airways may occasionally cause severe difficulty in breathing. Lymph nodes at the side of the neck may become enlarged and tender. The worst part of the illness usually lasts 4 to 7 days.


Lung infection (pneumonia) occurs in about 1 out of 400 people, especially adolescents and adults, resulting in cough and difficulty breathing.

Brain infection (encephalitis) is less common and causes unsteadiness in walking, headache, dizziness, confusion, and seizures. In adults, encephalitis can be life threatening. It occurs in 1 to 2 of 1,000 cases of chickenpox.

Heart infection sometimes causes a heart murmur.

Joint inflammation causes joint pain. Inflammation of the liver and problems with bleeding may also occur.

Reye syndrome, a rare but very severe complication that occurs almost only in those younger than 18, may begin 3 to 8 days after the rash begins (see Reye Syndrome). Giving infected children aspirin increases the risk.

Pregnant women who get varicella are at risk of serious complications, such as pneumonia, and may die as a result. If chickenpox develops during the 1st or early 2nd trimester, the fetus may become infected. Such an infection can result in scars on the skin, birth defects, and a low birth weight.

Risk of complications is also increased for people with a weakened immune system.


  • A doctor's evaluation

  • Rarely blood tests and testing of a sample taken from a sore

A doctor is usually certain of the diagnosis of chickenpox because the rash and the other symptoms are so typical.

Blood tests to measure levels of antibodies in the blood and laboratory tests to identify the virus (usually using a sample scraped from the sores) are rarely needed.


Healthy children nearly always recover from chickenpox without problems—only about 2 out of 100,000 children die. Before routine immunization, about 4 million people developed chickenpox annually in the United States, and about 100 of them (about half were children) died because of complications of chickenpox.

The infection is more severe in adults. About 30 out of 100,000 adults die.

Chickenpox is fatal in up to 15% of people with a weakened immune system.

When people who have been vaccinated develop chickenpox, the disease is less severe, and fewer of these people die.


In the United States, children are routinely vaccinated against varicella-zoster beginning at 12 months of age, with a second dose given at 4 to 6 years of age (see Vaccinating Infants and Children and Varicella Vaccine). The varicella vaccine contains weakened, live varicella virus. Older children and adults (particularly women of childbearing age and adults with chronic disorders) without immunity also may be vaccinated.

Certain people should not be vaccinated:

  • People with a weakened immune system, including those taking high doses of corticosteroids

  • Children who take aspirin regularly

  • Pregnant women and those who intend to become pregnant within 1 to 3 mo of vaccination

  • People who are more than slightly ill at the time of vaccination

Isolation of an infected person helps prevent the spread of infection to people who have not had chickenpox. Children should not return to school and adults should not return to work until the final blisters have crusted.

After exposure to chickenpox

Susceptible people who are at high risk of complications and who have been exposed to someone with chickenpox may be given antibodies against the varicella virus (varicella-zoster immune globulin). These people include those with leukemia or a weakened immune system, pregnant women who have not had chickenpox or the vaccine, and newborns whose mother developed chickenpox 5 days before or 2 days after delivery). Treatment with varicella-zoster immune globulin may prevent the infection or reduce its severity.


  • For people with mild cases, measures to relieve symptoms

  • For people at risk of moderate to severe symptoms, antiviral drugs

Mild cases of chickenpox require only the treatment of symptoms. Wet compresses on the skin help soothe itching, which may be intense, and prevent scratching, which may spread the infection and cause scars. Because of the risk of bacterial infection, the skin is bathed often with soap and water, the hands are kept clean, the nails are clipped to minimize scratching, and clothing is kept clean and dry. If the itching is severe, drugs that relieve itching, such as antihistamines, may be given by mouth. Taking colloidal oatmeal baths may also help. If a bacterial infection develops, antibiotics may be needed.

Doctors usually prescribe antiviral drugs, such as acyclovir, valacyclovir, and famciclovir, for all adolescents and for adults at risk of moderate to severe symptoms, including people with skin disorders such as eczema, those with chronic lung disease, and those with a weakened immune system. The drugs can slightly reduce the severity and duration of symptoms but must be given within 24 hours of the start of disease to be effective. These antiviral drugs are usually not given to healthy children or to pregnant women.

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