Varicella, commonly known as chickenpox, is a highly contagious viral infection that causes an itchy, blister-like rash across the body. This disease has affected millions of people worldwide, but thanks to vaccination efforts starting in the mid-1990s, cases have dramatically declined. Understanding how varicella spreads, who is at risk, and how to prevent it can help protect individuals and communities from this once-common childhood illness.

How Common Is Varicella Around the World?

Before the introduction of the chickenpox vaccine in 1995, varicella was extremely widespread in the United States. Nearly every child would contract chickenpox before reaching 9 years of age, making it one of the most common diseases of childhood.^[19] The disease was so prevalent that almost everyone got chickenpox at some point, usually as a toddler or young child.^[13]

The impact of vaccination has been remarkable. Since the late 1990s, the rate of chickenpox infections has declined by nearly 90%.^[13] More specifically, infections have gone down by 97% since the varicella vaccine became available.^[19] This dramatic reduction means that children today are far less likely to experience chickenpox than previous generations. However, the disease has not been completely eliminated, and outbreaks can still occur, particularly among unvaccinated populations.

In temperate climates, such as the Northeastern United States, chickenpox tends to occur most frequently during the late winter and early spring months.^[4] The seasonal pattern reflects how the virus spreads more easily when people spend more time indoors in close contact with others.

Today, most children in the United States receive a vaccine against chickenpox as part of their routine immunization schedule.^[13] This has fundamentally changed the landscape of the disease, transforming it from an almost universal childhood experience to a preventable infection that many young people will never encounter.

What Causes Varicella?

Varicella is caused by a specific virus called the varicella-zoster virus, often abbreviated as VZV.^[1] This virus belongs to the herpes virus family, which includes several other viruses that can infect humans.^[2] The varicella-zoster virus is unique because it causes two different diseases at different times in a person’s life. The first infection with VZV causes chickenpox, while reactivation of the virus years or even decades later can cause a condition called shingles or herpes zoster.^[3]

The virus is species-specific to humans, meaning it only infects people and cannot be transmitted to or from animals.^[8] When someone first encounters VZV, it enters the body through the respiratory system, including the nose, mouth, and throat.^[8] The virus then multiplies in the tonsils and spreads throughout the body, eventually reaching the skin where it causes the characteristic rash.^[8]

After a person recovers from chickenpox, the varicella-zoster virus does not leave the body completely. Instead, it remains dormant, or inactive, in nerve cells, particularly in the dorsal root ganglia in the spine.^[2] The virus can lie hidden there for many years without causing any symptoms. However, if the immune system becomes weakened due to aging, stress, illness, or certain medications, the virus can reactivate and travel along the nerves to the skin, causing shingles.^[2]

The varicella-zoster virus can survive in external environments for a few hours, though it spreads most effectively through direct person-to-person contact.^[8] Unlike some viruses that can remain infectious on surfaces for days, VZV does not live long outside the human body, which limits but does not eliminate the importance of environmental cleaning in preventing transmission.^[6]

How Does Chickenpox Spread?

Chickenpox is extraordinarily contagious, making it one of the most easily transmitted infectious diseases. The virus spreads primarily through two main routes: through the air and through direct contact with the rash.^[1] When an infected person coughs, sneezes, talks, or even breathes, they release tiny droplets of saliva and respiratory secretions into the air. These droplets contain the varicella-zoster virus and can be inhaled by people nearby, leading to infection.^[4]

Direct contact with the fluid from chickenpox blisters is another important way the disease spreads. The clear fluid inside the blisters is teeming with virus particles. If someone touches these blisters or items contaminated with the fluid, such as clothing, towels, or bedding, they can become infected.^[13] The disease can also spread when people share items with saliva on them, including cups, bottles, cans, forks, and spoons.^[4]

The contagious period for chickenpox is particularly concerning because infected individuals can spread the virus before they even know they are sick. A person with chickenpox is contagious starting 1 to 2 days before the rash appears, when they might only have a headache or feel slightly unwell.^[1] They remain contagious until all the chickenpox lesions have crusted over, forming scabs.^[1] This usually takes about 5 to 7 days after the rash first appears, though it can vary.

For vaccinated people who still get chickenpox, the transmission pattern is slightly different. These individuals may develop lesions that never form crusts or scabs. They are considered contagious until no new lesions have appeared for 24 hours.^[1]

The likelihood of transmission is remarkably high. Up to 90% of people who are not immune and have close contact with someone who has chickenpox will also become infected.^[1] This means that in a household where one unvaccinated child gets chickenpox, nearly all unvaccinated siblings are likely to develop the disease as well. Living in close quarters, such as dormitories or camps, significantly increases the risk of chickenpox spreading throughout the group.^[4]

After exposure to someone with chickenpox or shingles, it typically takes about 2 weeks before symptoms appear, though the incubation period can range from 10 to 21 days.^[1] During this time, the virus is multiplying in the body, but the infected person has no symptoms and does not yet know they are sick. The average incubation period is 14 days.^[8]

Who Is at Risk for Chickenpox?

Anyone who has never had chickenpox and has not been vaccinated against it can get the disease.^[1] This includes people of all ages, though the disease was historically most common in children. Today, with widespread vaccination, unvaccinated individuals of any age remain vulnerable to infection.

For most healthy children, chickenpox is generally a mild illness that causes discomfort but resolves without serious problems.^[5] However, certain groups of people face a much higher risk of developing severe complications from chickenpox. These high-risk groups require special attention and protection.

Infants, especially those less than 1 year old, are at increased risk for severe disease.^[9] Their immune systems are still developing, and they may not be able to fight off the virus as effectively as older children. Newborn babies whose mothers develop chickenpox symptoms between 5 days before and 2 days after delivery are at particularly high risk and may need special treatment.^[14]

Adolescents and adults who get chickenpox tend to experience more severe symptoms than young children. While adults account for only about 5% of reported chickenpox cases, they represent approximately 35% of deaths from the disease.^[9] Adults are more likely to develop complications such as pneumonia, which can be life-threatening.

Pregnant women who contract chickenpox face risks both for themselves and their unborn babies. The virus can harm the developing fetus during pregnancy, and infection near the time of delivery can be life-threatening for newborns.^[1] Women who are hoping to become pregnant and have never had chickenpox or been vaccinated should consider getting the vaccine before pregnancy.^[20]

People with weakened immune systems are especially vulnerable to severe chickenpox. This includes individuals with HIV/AIDS, cancer patients, people who have received organ transplants, and those taking medications that suppress the immune system, such as chemotherapy, immunosuppressive drugs, or long-term high-dose steroids.^[1] For these individuals, chickenpox can be serious and even life-threatening, requiring immediate medical attention and often antiviral medication.

People with chronic skin conditions or lung diseases also face higher risks of complications.^[11] Those with severe eczema may develop more extensive skin involvement, while individuals with chronic lung conditions are at greater risk for developing pneumonia.

What Are the Symptoms of Chickenpox?

The hallmark symptom of chickenpox is a distinctive rash that progresses through several stages. However, before the rash appears, many people experience early warning signs. These initial symptoms can include a low-grade fever, feeling unusually tired and weak, headache, and loss of appetite.^[7] Adults may have these symptoms for 1 to 2 days before the rash develops, while in children, the rash is often the first noticeable sign of illness.^[4]

The chickenpox rash typically appears 10 to 21 days after exposure to the virus.^[7] It usually starts on the face, chest, and back before spreading to the rest of the body, including the scalp, arms, legs, and even the mouth and genital area.^[1] The rash tends to be more concentrated on covered parts of the body, such as the trunk, rather than on exposed areas like the arms and legs.^[4]

The rash goes through three distinct stages, and all stages can be present on the body at the same time. This means a person can have new bumps forming while older ones are already healing.^[18] The first stage consists of raised red or pink bumps called papules, which look similar to small pimples or insect bites.^[7] These bumps appear in waves over 2 to 4 days.^[18]

The second stage develops when the bumps fill with clear fluid, forming thin-walled blisters called vesicles.^[7] These blisters are often described as looking like “dewdrops on a rose petal.” The blisters are very fragile and break easily, leaving open sores. This stage typically lasts about one to two days.^[13]

The third stage occurs when the broken blisters dry out and form crusts or scabs. These brown scabs gradually fall off over several days as the skin heals underneath.^[7] The entire process from the first bump to complete healing usually takes about 1 week, though the rash can last up to 10 days.^[1]

A person with chickenpox can develop anywhere from a few dozen to as many as 500 blisters.^[1] The typical case involves between 250 and 500 lesions.^[9] The rash is intensely itchy, which is one of the most uncomfortable aspects of the disease. The itching can be so severe that it interferes with sleep and daily activities.

Children who have been vaccinated against chickenpox but still get the disease usually experience much milder symptoms. These “breakthrough” infections typically involve fewer than 50 skin lesions, and the rash may look different, appearing as small raised bumps without progressing to fluid-filled blisters.^[5] Vaccinated individuals who get chickenpox also tend to have lower or no fever and recover more quickly than unvaccinated people.^[4]

In the most typical cases, chickenpox causes a fever up to 102°F (about 38.9°C) that lasts for 2 to 3 days.^[9] Most children experience malaise, itching, and fever as their main symptoms. The illness usually lasts about 4 to 7 days in total.^[1] During this time, children typically miss 5 to 6 days of school or childcare.^[1]

Can Chickenpox Lead to Serious Problems?

While chickenpox is often mild in healthy children, it can sometimes cause serious complications. The severity and type of complications vary depending on the person’s age and overall health. For most healthy children, complications are infrequent, but they do occur and can be severe.^[9]

The most common complication in children is bacterial infection of the skin lesions. When chickenpox blisters are scratched, bacteria can enter through the broken skin, causing infections that may require antibiotics.^[9] These secondary bacterial infections can involve the skin and soft tissues, sometimes spreading into deeper layers and even into the bloodstream, a condition called sepsis.^[5] Bacteria commonly responsible for these infections include Staphylococcus and Streptococcus species.

Pneumonia is another serious complication of chickenpox, occurring more frequently in adults than in children.^[9] This can be either direct viral pneumonia caused by the varicella-zoster virus itself or secondary bacterial pneumonia that develops after the initial viral infection. Adult cases of chickenpox carry a significantly higher risk of pneumonia compared to childhood cases.

Neurological complications, though rare, can be very serious. Encephalitis, or inflammation of the brain, can occur in people with chickenpox.^[4] Another neurological complication is cerebellar ataxia, which affects coordination and balance.^[5] These conditions require immediate medical attention and can have lasting effects.

Other potential complications include bleeding disorders, liver inflammation (hepatitis), and joint inflammation (arthritis).^[9] Chickenpox blisters can appear on the eyelids and inside the mouth, causing particular discomfort. Eye involvement requires careful monitoring to prevent complications that could affect vision.^[4]

Dehydration can become a problem, especially if mouth sores make it painful to eat or drink.^[6] Young children and people with multiple mouth blisters need encouragement to maintain adequate fluid intake during their illness.

The risk of complications varies significantly with age. People over 15 years old and infants under 1 year of age have much higher rates of complications compared to children between these ages.^[9] Although adults account for a small percentage of chickenpox cases, they represent a disproportionately large percentage of serious complications and deaths from the disease.

How Can Chickenpox Be Prevented?

The most effective way to prevent chickenpox is through vaccination. The chickenpox vaccine has transformed the landscape of this disease, dramatically reducing the number of cases, hospitalizations, and deaths. Everyone, including children, adolescents, and adults, should receive 2 doses of chickenpox vaccine if they have never had chickenpox or been vaccinated before.^[1]

For children, the standard vaccination schedule recommends the first dose between 12 and 15 months of age, with a second dose given between 15 and 23 months, or alternatively between 4 and 6 years of age.^[3] Depending on the specific vaccine used, the two doses should be given at least 4 to 6 weeks apart.^[20] The vaccine can be given at the same time as the MMR vaccine (which protects against measles, mumps, and rubella), or as a combination vaccine called MMRV that protects against all four diseases at once.^[20]

Children 12 years and younger who have not completed their chickenpox vaccinations can catch up by receiving two doses at least 3 months apart.^[6] Adolescents and adults 13 years and older who have never had chickenpox or been vaccinated should receive two doses 4 to 8 weeks apart.^[6] This is particularly important for adults because chickenpox tends to be more severe in this age group.

The chickenpox vaccine is very effective. About 90% of people who receive the vaccine are protected from getting chickenpox at all.^[13] Most people who get vaccinated will not develop the disease. However, the vaccine is not 100% effective, and some vaccinated individuals may still get chickenpox if exposed to the virus. The good news is that these “breakthrough” cases are usually very mild, with fewer blisters, lower fever, and faster recovery.^[1]

The vaccine also prevents almost all cases of severe illness.^[1] This means that even if a vaccinated person does get chickenpox, they are extremely unlikely to develop serious complications like pneumonia or encephalitis.

In some situations, the chickenpox vaccine can be given after exposure to the virus to prevent or lessen the severity of the disease. If given within a few days of exposure, the vaccine may still provide protection.^[1]

For people who cannot receive the vaccine, such as those with weakened immune systems or pregnant women, a product called varicella-zoster immune globulin (VariZIG) may be given after exposure to chickenpox. This contains antibodies against the varicella-zoster virus and can help reduce the severity of infection if given within 10 days of exposure, ideally within 4 days.^[14]

Pregnant women should not receive the chickenpox vaccine during pregnancy.^[6] Women who have never had chickenpox or been vaccinated should consider getting vaccinated before becoming pregnant to protect both themselves and their future babies.

Beyond vaccination, avoiding contact with infected individuals is important for prevention. People with chickenpox should stay home from school, childcare, or work until all blisters have crusted over.^[19] This isolation period helps prevent spreading the virus to others, particularly those who are at high risk for complications.

What Happens in the Body During Chickenpox?

Understanding what happens inside the body during a chickenpox infection helps explain why the disease causes its characteristic symptoms. When the varicella-zoster virus first enters the body through the respiratory tract, it begins multiplying in the tonsils and lymph nodes in the throat.^[2] From there, the virus moves into the lymphatic system, which is part of the body’s immune defense network.

The virus then spreads throughout the entire body via the bloodstream, a process called viremia. This widespread distribution of the virus explains why the chickenpox rash appears all over the body rather than in just one location. Eventually, the virus reaches the skin, where it infects cells and causes the characteristic itchy rash and blisters.^[2]

The chickenpox blisters form when the virus damages skin cells, causing fluid to accumulate between layers of skin. The fluid inside these blisters contains millions of virus particles, which is why direct contact with the blisters can spread the infection. The intense itching associated with chickenpox occurs because the immune system responds to the viral infection in the skin, releasing chemicals that trigger itch sensations.

During the active infection, the body’s immune system works hard to fight off the virus. This immune response causes many of the symptoms people experience, including fever, tiredness, and general malaise. The fever represents the body’s attempt to create an environment less favorable for viral replication, while fatigue reflects the energy demands of mounting an immune response.

As the immune system gains control over the infection, new blisters stop forming and existing ones begin to heal. The blisters dry out and form scabs as the body repairs the damaged skin. This healing process usually takes about a week from the time the rash first appears.

However, the varicella-zoster virus is never completely eliminated from the body. As the active infection resolves, some virus particles travel along nerve fibers to reach nerve cell bodies in the spinal cord and other ganglia. There, the virus enters a dormant state, hiding within nerve cells where the immune system cannot detect or eliminate it.^[2] The virus remains latent in these neurons, sometimes for many decades, without causing any symptoms or problems.

Later in life, particularly when the immune system becomes weakened, the dormant virus can reactivate. This reactivation causes the virus to travel back down the nerve to the skin, where it produces a painful rash known as shingles or herpes zoster. Shingles typically affects only one side of the body and follows the path of a single nerve, unlike the widespread distribution of chickenpox.^[2]

The likelihood of the virus reactivating increases with age, particularly in people over 50 years old. Other factors that can trigger reactivation include stress, illness, immunosuppressive medications, and conditions that weaken the immune system.^[2] About one-third of people who have had chickenpox will develop shingles at some point in their lives.^[8]

The varicella-zoster virus can also affect other parts of the body beyond the skin. In some cases, particularly in people with weakened immune systems, the virus can spread to internal organs or the central nervous system. When VZV infects the brain or the membranes surrounding it, this can cause meningitis, encephalitis, or a combined condition called meningoencephalitis.^[2] These serious complications result from direct viral damage to nervous system tissues combined with inflammation triggered by the immune response.

Reactivation of the varicella-zoster virus around the eye causes a condition called herpes zoster ophthalmicus or eye shingles, which can threaten vision if not treated promptly.^[2] When the virus reactivates in nerves of the face, it can cause Ramsay Hunt syndrome, which may result in facial paralysis, earache, and hearing problems.^[2]