Chickenpox (varicella)

Chickenpox (varicella) is a highly contagious illness caused by the varicella-zoster virus. It causes an itchy rash with fluid-filled blisters that eventually scab over, along with fever and fatigue. Before widespread vaccination, nearly all children developed chickenpox. The disease is usually mild in healthy children but can be more severe in infants, adolescents, adults, pregnant people, and those with weakened immune systems.

Vaccination has dramatically reduced cases, hospitalizations, and deaths. The same virus that causes chickenpox can reactivate years later as shingles. People who have had chickenpox or the vaccine usually have lasting protection against a second bout of chickenpox, though reinfection is possible but uncommon.

Symptoms typically appear 10–21 days after exposure and may include:

• Fever, loss of appetite, headache, and fatigue for 1–2 days before the rash (or appearing with the rash)
• An itchy rash that progresses from flat red spots to raised bumps to fluid-filled blisters (vesicles), then crusts and scabs
• Rash that often starts on the chest, back, and face, then spreads; new waves of spots appear over several days so different stages are present at once
• Blisters can also occur in the mouth, eyelids, and genital area
• In vaccinated people who still get chickenpox (breakthrough), the illness is often milder with fewer spots

Adults and immunocompromised people may have more severe rash and systemic symptoms.

Chickenpox is caused by primary infection with varicella-zoster virus. It spreads easily through respiratory droplets and by direct contact with fluid from the blisters. A person is contagious from about 1–2 days before the rash appears until all lesions have crusted. The virus can also spread from someone with shingles to a person who never had chickenpox or the vaccine, causing chickenpox (not shingles) in the newly infected person.

Anyone who has not had chickenpox or the vaccine can get infected. Higher risk of severe disease includes:

• Newborns and infants
• Adolescents and adults
• Pregnant people (risk to both parent and fetus/newborn)
• Immunocompromised people (cancer treatment, transplant, high-dose steroids, HIV, etc.)
• People with certain skin conditions such as eczema

Possible complications include:

• Bacterial skin infection of the lesions
• Pneumonia (more common in adults)
• Encephalitis or cerebellar ataxia (uncommon)
• Dehydration
• Bleeding problems (rare)
• Toxic shock syndrome (rare)
• In pregnancy: risk of congenital varicella syndrome if infection occurs early, and severe newborn disease if the parent develops chickenpox near delivery
• Later reactivation as shingles

The varicella vaccine is the best prevention. Routine two-dose vaccination is recommended for children, and catch-up vaccination for susceptible older children and adults. People who should not receive the live vaccine (including some immunocompromised people and pregnant people) need other protections, including avoiding exposure and, after significant exposure, possible varicella-zoster immune globulin or antivirals as advised by a clinician. Infected people should stay home until all lesions have crusted and avoid contact with high-risk individuals.

Diagnosis is usually clinical based on the characteristic rash and exposure history. When confirmation is needed (atypical cases, immunocompromised patients, or public-health investigation), PCR testing of lesion fluid is preferred. Blood tests for antibodies can assess immunity but are less useful for acute diagnosis.

Contact a clinician if chickenpox occurs in a newborn, adolescent, adult, pregnant person, or someone with a weakened immune system, or if the rash spreads near the eyes. Seek urgent care for difficulty breathing, stiff neck, severe headache, repeated vomiting, confusion, high fever that persists, signs of skin infection (increasing redness, swelling, severe pain), or dehydration. People with chickenpox should not use aspirin because of the risk of Reye’s syndrome.

For healthy children with mild disease, treatment is mainly supportive:

• Calamine lotion, cool baths with colloidal oatmeal, and antihistamines for itch
• Acetaminophen for fever (never aspirin in children or teenagers with chickenpox)
• Trim fingernails to reduce skin damage from scratching
• Stay hydrated and rest

Antiviral medicine (acyclovir or similar) is recommended for people at higher risk of severe disease — including adolescents, adults, pregnant people in some situations, and immunocompromised patients — and is most effective when started early. Severe disease may require hospital care and intravenous antivirals.

At home:

• Use supportive measures for itch and fever as above
• Keep the skin clean; avoid sharing towels and clothing
• Stay home from school, work, and public places until all blisters have crusted
• Avoid contact with newborns, pregnant people, and immunocompromised individuals
• Do not use aspirin
• Call a clinician if symptoms worsen or warning signs appear

Bring:

• Vaccination history and any prior chickenpox illness
• Timing of exposure and rash onset
• Immune status, pregnancy status, and chronic conditions
• Photos of the rash if helpful
• Questions about antivirals, return to school, and protecting household members