Chickenpox is the common clinical name for primary infection with varicella-zoster virus, or VZV, a herpesvirus. It typically causes a generalised, itchy vesicular rash accompanied by fever and malaise. Lesions characteristically appear in successive crops, so macules, papules, vesicles and crusted lesions may coexist at the same time. Chickenpox is highly contagious and spreads primarily through respiratory transmission and direct contact with fluid from skin lesions. After primary infection, the virus remains latent in sensory nerve tissue and can later reactivate as shingles.
VZV enters through the respiratory tract or conjunctiva and undergoes replication before spreading through the bloodstream to the skin and other tissues. The incubation period is usually about two weeks, commonly within a range of roughly 10 to 21 days. People can transmit infection before the rash is fully apparent and remain contagious until the lesions have crusted. The disease is often more severe in adults than in healthy young children, although serious complications can occur at any age. Previous infection generally produces long-lasting immunity, while vaccination provides an alternative route to protection.
The characteristic rash is intensely pruritic and progresses through several stages. Early lesions become fluid-filled vesicles before crusting, and new lesions can continue to appear while older ones are healing. Scratching can damage the skin barrier and facilitate secondary bacterial infection. Other symptoms include fever, tiredness, headache and reduced appetite. The distribution is often concentrated on the trunk and face but can involve the scalp and mucous membranes. The simultaneous presence of lesions at different stages helps distinguish chickenpox from some other vesicular diseases.
Complications include bacterial infection of skin lesions, pneumonia, cerebellar ataxia, encephalitis and dehydration. Severe disease is more likely in adults, newborns, pregnant people and individuals with weakened immune systems. Maternal varicella during pregnancy can create risks for both the pregnant person and fetus, while infection around the time of delivery can be particularly serious for the newborn. The virus can also cause severe disseminated disease in people with impaired cellular immunity. These risks explain why apparently ordinary childhood chickenpox is not medically trivial in every circumstance.
Diagnosis is frequently clinical when the characteristic rash is present, although laboratory testing can be useful for atypical presentations, vulnerable patients or epidemiological investigations. Polymerase chain reaction testing of lesion material is highly useful when laboratory confirmation is required. Treatment is often supportive in otherwise healthy children, but antiviral therapy such as aciclovir may be considered for people at increased risk of complications or with severe disease, according to clinical guidance. Antiviral treatment is generally most effective when started early in the course of illness.
Prevention includes vaccination with a live attenuated varicella vaccine in countries and programmes where it is recommended. Post-exposure management can include vaccination for suitable susceptible individuals and, in selected high-risk circumstances, administration of varicella-zoster immunoglobulin. Because chickenpox spreads readily, identifying significant exposures is particularly important for pregnant people and those with impaired immunity. Isolation from susceptible individuals during the contagious period helps reduce transmission.
Chickenpox and shingles are caused by the same virus but represent different stages of infection. Chickenpox is primary VZV infection, whereas shingles is reactivation of latent VZV. Chickenpox is also different from smallpox, despite superficial similarities in older descriptions; smallpox was caused by variola virus and has been eradicated. Another misconception is that scratching merely causes cosmetic problems; damaged lesions can become portals for bacterial infection. Antibiotics do not treat VZV itself, although they may be required for secondary bacterial infection.
Chickenpox has substantial public-health significance because its high transmissibility can produce outbreaks in schools, households and other communities. Vaccination programmes have reduced incidence and complications in countries that use routine varicella immunisation. The disease also has lifelong biological significance because latent VZV persists after recovery and can reactivate decades later. Understanding this latent phase is essential for understanding why a person who previously had chickenpox can subsequently develop shingles, and why VZV remains clinically relevant long after the original rash has disappeared.
