Chickenpox is a highly contagious viral infection that causes an itchy, blister-like rash across the body. It’s caused by the varicella-zoster virus, a member of the herpesvirus family, and primarily affects children, though adults who haven’t been vaccinated or previously infected can get it too. Before widespread vaccination began in the 1990s, nearly every child in the United States got chickenpox. Today, two doses of the vaccine prevent about 92% of cases.
How Chickenpox Spreads
The varicella-zoster virus enters the body through the upper respiratory tract. After you breathe in viral particles or touch fluid from an infected person’s blisters, the virus begins replicating in the cells lining your airway. From there, it spreads through the bloodstream to the skin, where it produces the characteristic rash.
The incubation period, meaning the time between exposure and first symptoms, is typically 14 to 16 days, though it can range from 10 to 21 days. A person becomes contagious one to two days before the rash appears and stays contagious until every blister has crusted over, which usually takes four to five days after the rash starts. This early contagious window, before anyone can see the rash, is one reason chickenpox spreads so easily through households and classrooms.
What the Rash Looks Like
The rash typically starts on the scalp, face, and trunk before spreading outward to the arms and legs. It begins as small, flat red spots that quickly progress through several stages over the course of 12 to 14 hours: raised bumps, fluid-filled blisters, cloudy pustules, and finally crusted scabs. New crops of spots continue appearing for several days, so you’ll often see all stages of the rash on the body at the same time. That mix of fresh blisters alongside healing scabs is one of the hallmarks that distinguishes chickenpox from other rashes.
Before the rash shows up, most people experience a day or two of fever, fatigue, headache, and loss of appetite. Children tend to have milder symptoms overall, while adolescents and adults often develop more blisters and feel significantly worse.
Who Faces the Greatest Risk
For most healthy children, chickenpox is uncomfortable but resolves on its own within a week or two. Serious complications are uncommon in this group, though bacterial skin infections (particularly from scratching open blisters) are the most frequent issue in kids.
Certain groups face a much higher risk of severe disease:
- Infants too young to be vaccinated
- Adolescents and adults who never had chickenpox or the vaccine
- Pregnant women, for whom infection can also harm the developing baby
- People with weakened immune systems, including those with HIV/AIDS, cancer patients on chemotherapy, organ transplant recipients, and anyone on long-term steroid or immunosuppressive therapy
In these groups, chickenpox can lead to pneumonia, brain inflammation (encephalitis), bloodstream infections, hemorrhagic complications, and severe dehydration. Pneumonia is the complication most likely to affect adults, while bacterial skin infections are more common in children.
How Chickenpox Is Diagnosed
Most of the time, a doctor can diagnose chickenpox just by looking at the rash. The combination of blisters in multiple stages, their typical distribution starting on the trunk, and the accompanying fever makes it fairly recognizable. In less clear-cut cases, or when it’s important to confirm the diagnosis (during outbreaks, severe illness, or in vaccinated individuals who develop a milder version), a lab test called PCR can detect the virus’s genetic material in fluid or scabs from the blisters. PCR is the most reliable confirmation method and works for both unvaccinated and vaccinated people.
Treatment and Symptom Relief
For healthy children, treatment focuses on managing symptoms. Cool baths, calamine lotion, and antihistamines can help control itching. Keeping fingernails short and, for young children, using mittens at night reduces the risk of scratching blisters open and introducing bacteria.
One critical safety point: never give aspirin or aspirin-containing products to children or teenagers with chickenpox. Aspirin use during a viral illness like chickenpox is linked to Reye’s syndrome, a rare but potentially life-threatening condition in which the liver swells, blood sugar drops, and ammonia builds up in the blood. Early signs include persistent vomiting and unusual sleepiness. If fever relief is needed, acetaminophen is the safer choice.
Antiviral medication may be prescribed for people at higher risk of complications, including adults, pregnant women, and those with compromised immune systems. When started early in the illness, antivirals can reduce the severity of symptoms and shorten the duration of the rash. For otherwise healthy children, antivirals are not routinely recommended.
The Link Between Chickenpox and Shingles
Once you recover from chickenpox, the virus doesn’t leave your body. Instead, it travels along nerve fibers and settles into clusters of nerve cells called ganglia, located along the spine, near the base of the skull, and in the autonomic nervous system. There, it enters a dormant state that can last for decades. During this time, the virus keeps a tiny portion of its genetic code active, just enough to maintain its foothold without triggering symptoms.
Years or even decades later, the virus can reactivate and travel back along a nerve to the skin, causing shingles: a painful, blistering rash that typically appears in a band on one side of the body. Reactivation is more common when the immune system weakens, whether from aging, stress, illness, or medications that suppress immune function. Roughly one in three people who had chickenpox will eventually develop shingles. A separate shingles vaccine, recommended for adults 50 and older, significantly reduces this risk.
How Vaccination Works
The varicella vaccine is the most effective way to prevent chickenpox. The CDC recommends two doses for children: the first between 12 and 15 months of age, and the second between ages 4 and 6. Adolescents and adults aged 13 or older who were never vaccinated or infected should receive two doses spaced four to eight weeks apart.
A single dose provides about 82% protection against chickenpox of any severity, while the full two-dose series raises that to 92%. Breakthrough infections can still occur in vaccinated people, but they tend to be much milder, with fewer blisters, less fever, and faster recovery. One-dose recipients are more likely to experience breakthrough infection than those who received both doses.
Vaccinated individuals who do develop chickenpox sometimes get flat, reddish spots that never form true blisters and don’t crust over in the usual way. These people are considered contagious until no new spots have appeared for 24 hours, rather than waiting for crusting.