Chickenpox is a contagious disease caused by the varicella-zoster virus, a member of the herpes family. It spreads easily through the air when infected people sneeze or cough, or through contact with an infected individual’s chickenpox blisters. Because chickenpox is so contagious, people who have never had chickenpox nor been vaccinated against it can become infected by being in a room with an infected person; however, momentary exposure is not likely to result in infection.

In temperate climates, chickenpox tends to be a childhood disease, with peak incidence among preschool and school-aged children during late winter and early spring. In tropical climates, infection occurs later during childhood and adolescence, causing higher susceptibility among adults. In most developed countries, healthy children routinely receive the chickenpox vaccine, resulting in a substantial decline in the incidence of the disease. The risk of exposure is higher in most other parts of the world.

Early symptoms appear 10 to 21 days after exposure and include body aches, fever, fatigue and irritability. A rash then appears and develops into 250 to 500 itchy blisters over the entire body and sometimes in the mouth and other internal areas. The blisters last five to seven days and heal with scabs. The illness is usually not severe, but risk of hospitalization and death increases among adolescents and adults. Persons who were vaccinated against chickenpox sometimes develop a mild case with 50 or fewer red bumps that rarely blister.

While waiting to see your doctor, take acetaminophen or ibuprofen to reduce fever. Do not give aspirin or medication containing aspirin to anyone with chickenpox, child or adult, since it has been associated with the life-threatening Reye’s syndrome. Rest as much as possible and avoid contact with others. Chickenpox is highly contagious until the skin lesions have fully crusted. Health care providers diagnose chickenpox by the telltale rash; if there is doubt, a blood sample or lesion samples may be sent to the lab. In otherwise healthy children, chickenpox requires no medical treatment, although an antihistamine may relieve itching.

Let your health care provider know immediately if the rash spreads to one or both eyes; if it gets very red, warm or tender, indicating a possible bacterial infection; or if you experience dizziness, disorientation, shortness of breath, tremors, loss of muscle coordination, worsening cough, vomiting, stiff neck or a fever greater than 103 degrees.

In high-risk people, chickenpox can lead to complications such as bacterial infections of the skin, soft tissues, bones, joints or bloodstream (sepsis); pneumonia; inflammation of the brain (encephalitis); or toxic shock syndrome. Those at high risk of complications include newborns and infants who have never had chickenpox or the vaccine; adults, especially pregnant women, who have not had chickenpox; people who are immunocompromised from medication such as chemotherapy or steroids or a disease such as cancer or HIV; and people who take drugs that suppress the immune system.

For those at risk, antiviral medicines such as acyclovir or immune globulin intravenously may lessen the severity if given within 24 hours after the rash appears. Other antiviral drugs such as famciclovir and valacyclovir are approved only for adults. Treatment of skin infections and pneumonia may require antibiotics. Hospitalization and supportive care may be required.

Being exposed to chickenpox early in pregnancy can cause low birth weight and birth defects such as limb abnormalities, cataracts, abnormal development of the brain and mental retardation. A greater threat occurs when the mother develops chickenpox in the week before birth; it can cause a serious, life-threatening infection in a newborn. If you are pregnant and not immune to chickenpox, talk to your doctor.

Studies have found the chickenpox vaccine to be safe and effective. Side effects are generally mild and include redness, soreness, swelling and, rarely, small bumps at the site of the shot. Children who have never had chickenpox should get two doses of the vaccine, with the first dose administered at 12 to 15 months of age and the second at ages 4 to 6 years. Two doses, four to eight weeks apart, are recommended for people 13 years or older. Women should avoid pregnancy for four weeks after vaccination, and pregnant women cannot receive the vaccine.

If you have had chickenpox, you are probably immune for life; it is possible but not common to get it again. Following chickenpox, however, the virus remains dormant in nerve cells and may be reactivated, causing herpes zoster, or shingles. Shingles generally occurs in adults older than 50 years, emerging during a period of stress or when immunocompromised. The painful rash may cause permanent nerve damage or lead to postherpetic neuralgia, with the pain persisting long after blisters disappear. A shingles vaccine (Zostavac) is recommended for adults 60 and older who have had chickenpox.

People traveling or living abroad should ensure they are immune to chickenpox. According to the Centers for Disease Control, evidence of immunity includes documentation of age-appropriate vaccination; laboratory tests to determine immunity or disease; a history of prior chickenpox or shingles infection; or being born in the United States before 1980, when the disease was prevalent. Age alone does not constitute evidence for health care personnel or those at high risk.

The content of this article is for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition.