Chickenpox

• 1. Introduction

  ›

  Chickenpox earned its first documented mention in 1658, and ever since, people have argued about where the name came from. Some traced it to chickpeas, claiming the tiny blisters looked like the legumes scattered across the skin. Others said the rash resembled the marks left by a chicken's pecking beak. Samuel Johnson offered a blunter theory. He explained the name as coming from the disease being of no very great danger. That casual dismissal hides a stranger truth. The virus behind those itchy blisters does not leave when the rash heals. It hides in the body's nerve tissue and waits, sometimes for fifty years, before returning under a different name. How does a childhood illness become a disease of the elderly? Why did doctors fail to tell it apart from a far deadlier rash until the late nineteenth century? And what makes a mild infection in a five-year-old a grave threat to a pregnant woman or a newborn? The answers begin with a single virus that learned to live with us permanently.

• 2. The Virus And Its Spread

  ›

  Varicella zoster virus belongs to the herpesvirus family, and it travels through the air with unsettling ease. An infected person coughs or sneezes, and the virus spreads through respiratory droplets. The infection rate in close contacts reaches 90 percent. That makes it one of the most transmissible diseases a child can catch. The incubation period runs from 10 to 21 days before the rash ever appears. Contagiousness begins one to two days before the disease can be recognized, because watery nasal discharge carrying live virus precedes both the external rash and the oral ulcers. A person spreads the virus until every vesicular lesion has dried into a crust, which usually takes four or five days. By then, nasal shedding of live virus ceases. The virus also passes through direct contact with the blisters themselves. There is an odd twist in transmission. Someone with shingles can give chickenpox to a person who is not immune, through contact with their blisters. The virus is also fragile outside the body. Like all enveloped viruses, it is sensitive to drying, heat, and detergents, and it is susceptible to chlorine bleach, or sodium hypochlorite.

• 3. The Rash And Its Course

  ›

  The rash begins as small red dots on the face, scalp, torso, upper arms, and legs. Over 10 to 12 hours, those dots progress into small bumps, then blisters, then pustules, before they umbilicate and form scabs. At the blister stage, intense itching usually sets in. Blisters can also appear on the palms, the soles, and the genital area. Inside the mouth, the disease often shows itself differently. Small ulcers develop in the oral cavity and tonsil areas, painful or itchy or both. This internal rash, the enanthem, can precede the external rash, the exanthem, by one to three days, or appear at the same time. Symptoms typically surface 10 to 21 days after exposure to a contagious person. In adolescents and adults, the illness opens with early prodromal symptoms: nausea, loss of appetite, aching muscles, and headache, followed by malaise and a low-grade fever. Children rarely get this warning. For them, the first sign is the rash or the spots inside the mouth. The whole episode usually resolves on its own within a week or two, though the rash itself may linger for up to a month. The appearance of new blisters begins to subside after the fifth day.

• 4. When It Turns Dangerous

  ›

  Up to 10 percent of pregnant women with chickenpox develop pneumonia, and the severity increases the later it strikes in gestation. The disease, mild in young children, grows more severe with age and more dangerous in certain bodies. It is generally worse in adult men than in women or children. Non-immune pregnant women and people with suppressed immune systems face the highest risk of serious complications. In England and Wales, 75 percent of deaths due to chickenpox occur in adults. The list of complications stretches far beyond an itchy week. In adults, infection brings greater morbidity and mortality from pneumonia, bronchitis, hepatitis, and encephalitis. Ninety percent of cases of varicella pneumonia occur in the adult population. Secondary bacterial infection of the skin lesions, showing up as impetigo, cellulitis, and erysipelas, is the most common complication in healthy children. The virus can even reach the blood vessels. Arterial ischemic stroke associated with chickenpox in the previous year accounts for nearly one-third of childhood arterial ischemic stroke. Among the rarest and most feared outcomes are the hemorrhagic syndromes. Five have been described, and one of them, malignant chickenpox with purpura, carries a mortality rate greater than 70 percent. The cause of these hemorrhagic syndromes is not known.

• 5. Threat To The Unborn

  ›

  If infection strikes during the first 28 weeks of gestation, it can produce fetal varicella syndrome. The danger to the fetus from a primary infection is greatest in the first six months of pregnancy, when the virus can cross the placenta and infect the developing child. The effects range from underdeveloped toes and fingers to severe anal and bladder malformation. The damage can reach the brain, causing encephalitis, microcephaly, hydrocephaly, or aplasia of the brain. It can reach the eye, producing microphthalmia, cataracts, chorioretinitis, or optic atrophy. It can leave skin lesions and patches of hypopigmentation. Timing near birth creates its own peril. Infection late in gestation or just after birth is called neonatal varicella. The risk to the baby is greatest when the mother is exposed in the window from seven days before delivery to eight days after the birth. Newborns who develop symptoms face a high risk of pneumonia and other serious complications. There is one natural defense at work here. Antibodies a mother produces from immunization or previous infection cross the placenta to the fetus, which is why a baby exposed by infectious siblings is of less concern when the mother is immune.

• 6. The Virus That Comes Back

  ›

  After the rash heals, varicella zoster virus does not leave the body. It retreats into the dorsal ganglion cells of the sensory nerves and remains latent, dormant in nerve tissue for about fifty years. The immune system holds it in check. But when that defense weakens, the virus can reactivate as an entirely different illness called shingles, or herpes zoster. This is the most common late complication of chickenpox, surfacing decades after the original, often childhood, infection. Shingles affects one in five adults who had chickenpox as children. The risk climbs for those who are immune-suppressed, particularly from cancer, HIV, or other conditions, and stress can bring it on, though scientists are still studying that link. Adults over 60 who had chickenpox but not shingles are the most prone age group. Because the immune system weakens with age, the United States Advisory Committee on Immunization Practices suggests every adult over 50 get the herpes zoster vaccine. In England, a routine shingles vaccination programme for adults aged 70 to 80 began in 2013. The reactivating virus can also strike the arteries of the neck and head, producing a stroke, either in childhood or after a latency period of many years.

• 7. The Vaccine And Its Paradox

  ›

  Michiaki Takahashi and his colleagues in Japan developed a live attenuated varicella vaccine, the Oka strain, in the early 1970s. In 1995, Merck and Co. licensed the Oka strain in the United States, and Maurice Hilleman's team at Merck invented a varicella vaccine that same year. Since its introduction in 1995, the vaccine has driven down both cases and complications. It protects about 70 to 90 percent of people, with a greater benefit against severe disease. A second dose is recommended five years after the first. Even a vaccinated person who gets infected is likely to have a milder case. The vaccine raised a genuine puzzle for public health. Being exposed to chickenpox as an adult, through contact with infected children, may boost immunity to shingles. So planners worried that vaccinating most children would strip adults of that natural boost, lowering immunity and causing more shingles. The counterargument is that exposure to children with varicella may not be critical to maintaining immunity. Multiple subclinical reactivations of the virus may happen spontaneously, providing an internal boost against zoster without ever causing illness. Policy reflects this tension. In the UK as of 2014, the vaccine was recommended only for the particularly vulnerable, deliberately keeping the virus in circulation. That changed when the Joint Committee on Vaccination and Immunisation recommended in November 2023 that all children be vaccinated at 12 months and 18 months. The programme was inaugurated in January 2026.

• 8. Living With The Itch

  ›

  Calamine lotion, a topical barrier containing zinc oxide, is one of the most commonly used interventions, despite no formal clinical studies of its effectiveness, and it carries an excellent safety profile. Most treatment simply eases symptoms while the immune system does the real work. Cutting fingernails short or wearing gloves prevents scratching and reduces the risk of secondary infection. For children, keeping nails short and clean matters especially, since they scratch their blisters more deeply than adults. One medicine carries a stark warning. Paracetamol, also called acetaminophen, can reduce fever, but aspirin must not be used. Aspirin given to someone with chickenpox may cause Reye syndrome, a serious and sometimes fatal disease of the liver and brain. It is highly contraindicated in children younger than 16. Antivirals occupy a careful middle ground. Aciclovir taken by mouth within 24 hours of rash onset shortens symptoms by one day but does not change complication rates, so it is not recommended for people with normal immune function. For adults, who tend to have more severe infections, treatment with aciclovir or valaciclovir is generally advised if started within 24 to 48 hours of the rash. People at high risk who have had significant exposure may receive varicella zoster immune globulin to ward off the disease. Because the danger of catching it as an adult is real, some parents take the opposite approach, deliberately exposing children at chickenpox parties, even as doctors warn the vaccine is the safer path. Humans are the only species the disease affects naturally, though it has been induced in chimpanzees and gorillas.