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Kenneth M. Kaye

, MD, Harvard Medical School

Last full review/revision Apr 2020| Content last modified Apr 2020

Chickenpox is a highly contagious viral 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. It is caused by the varicella-zoster virus, which is a type of herpesvirus (herpesvirus type 3).

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 approximately 90%. However, in some countries, the vaccine is not available or is not included as a routinely recommended childhood vaccine.

A person with chickenpox is contagious from 2 days before the rash appears and 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, or liver. 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 inactive (dormant) in the body after an initial infection with chickenpox, sometimes reactivating in later life, causing shingles. A shingles (herpes zoster) vaccine is available for older adults. This vaccine may decrease the risk of developing shingles in later life.

Transmission of chickenpox

Chickenpox is spread in the following ways:

  • Through airborne droplets of moisture containing the varicella-zoster virus
  • Through contact with the rash caused by chickenpox or shingles
  • From a pregnant women to the fetus

Symptoms of Chickenpox

Symptoms of chickenpox begin 7 to 21 days after infection occurs. 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 people 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. It forms an itchy, round, fluid-filled blister against a red background and finally crusts. Spots continue to develop and crust for several days. A hallmark of chickenpox is that the rash develops in crops so that the spots are in various forms of development at any affected area. Very rarely, the spots become infected by bacteria, which can cause a severe skin infection (cellulitis or necrotizing fasciitis).

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. The worst part of the illness usually lasts 4 to 7 days.


Risk of complications from chickenpox is increased for newborns, adults, and people who have a weakened immune system or certain disorders.

Lung infection (pneumonia) occurs in about 1 out of 400 adults, resulting in cough and difficulty breathing. Pneumonia rarely develops in young children who have a normal immune system.

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.

Inflammation of the liver and bleeding problems may also occur.

Reye syndrome is a rare but very severe complication that occurs almost only in those younger than 18 following the use of aspirin. Therefore, aspirin should not be given to children with chickenpox. Reye syndrome may begin 3 to 8 days after the rash begins.

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

Diagnosis of Chickenpox

  • 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. (Antibodies are produced by the immune system to help defend the body against a particular attacker, such as the varicella-zoster virus.)

Prognosis of Chickenpox

Healthy children nearly always recover from chickenpox without problems. Before routine immunization, about 4 million people developed chickenpox annually in the United States, and about 100 to 150 of them died each year because of complications of chickenpox.

In adults, chickenpox is more severe, and the risk of dying is higher.

Chickenpox is particularly severe in 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.

Prevention of Chickenpox

  • Vaccination
  • Sometimes immune globulin


The varicella vaccine contains weakened, live varicella virus. There are 3 formulations of the vaccine in the United States:

  • Standard dose varicella vaccine
  • Combination measles-mumps-rubella-varicella (MMRV) vaccine
  • Higher dose vaccine used to prevent herpes zoster (see herpes zoster vaccine

In the United States, children are routinely vaccinated against varicella-zoster. They are given two doses: one at 12 to 15 months of age, with the second given at 4 to 6 years of age (see Routine Vaccinations for Infants, Children, and Adolescents).

Older children and adults (particularly women of childbearing age and adults with chronic disorders) who have not had chickenpox and have not been vaccinated may also be vaccinated. They are given two doses 4 to 8 weeks apart.

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

Preventing spread of chickenpox

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
  • 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.

If healthy people have been exposed to chickenpox and have not already been vaccinated, vaccination within 3 to 5 days of exposure can help prevent chickenpox or reduce its severity.

Treatment of Chickenpox

  • For people with mild cases, measures to relieve symptoms
  • For people at risk of moderate to severe symptoms, antiviral drugs

Mild cases of chickenpox in children 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 (see table Some Antiviral Drugs for Herpesvirus Infections), by mouth to certain healthy people at risk of moderate to severe disease, including people

  • 12 years of age or older 
  • With skin disorders such as eczema
  • With chronic lung disease

For people over 1 year of age who have a weakened immune system, doctors may prescribe acyclovir given by vein (IV).

Antiviral drugs can reduce the severity and duration of symptoms and should be given within 24 hours of the start of disease, if possible.

Because pregnant women are at high risk of severe complications from chickenpox, some experts recommend treating pregnant women who have chickenpox with acyclovir or valacyclovir.

Drugs Mentioned In This Article

Generic Name Select Brand Names
immune globulin Gammagard S/D
valacyclovir VALTREX
famciclovir FAMVIR
acyclovir ZOVIRAX
aspirin No US brand name

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