Chickenpox is a very common illness caused by the varicella-zoster virus. It's extremely contagious. The rash that it produces is usually harmless and goes away on its own.
While you can get chickenpox at any age, most cases occur before the age of 14. Anyone who's had the disease once is usually immune for life, although they can still get shingles, a painful skin rash caused when the varicella-zoster virus becomes active again, even many years after they've had chickenpox.
Chickenpox usually occurs in late winter and early spring. Since the introduction of the chickenpox vaccine, many children never get chickenpox.
The varicella-zoster virus may be spread through the air or by direct contact with the blisters (lesions) of someone infected with chickenpox or shingles.
Once someone is infected, the virus usually incubates for 14 to 16 days before a rash appears, although incubation can last from 10 days to 21 days. There are no symptoms during incubation and a person is contagious from 1 to 2 days before symptoms appear. The person remains contagious until all the blisters have dried and scabs have formed.
Flu-like symptoms start to develop a day or two before an itchy red rash appears. Fatigue, mild headache, fever, chills, and muscle or joint aches are typical. The rash emerges as raised red bumps that turn to teardrop-shaped blisters that are extremely itchy.
These blisters may appear anywhere on the body, usually starting on the scalp, spreading to the trunk or torso, and then to the arms, legs, and face. In some cases, the rash may even spread across your entire body, including areas such as the throat, mouth, and vagina.
The blisters come in waves, with new crops developing as old ones burst. New blisters stop forming within about 5 days. By the sixth day, most blisters will have burst, dried, and crusted over. 2 weeks after that, most of the scabs will have disappeared.
Children usually have a much milder infection and recover faster than adults. Babies, adults, and those with weakened immune systems tend to have more severe and longer-lasting symptoms. They are at higher risk of developing complications, including inflammation of the brain (encephalitis) and pneumonia.
Newborns whose mothers develop chickenpox during early pregnancy are at risk for low birth weight and birth defects. If the mother develops chickenpox a week before birth, the newborn is at risk for a life-threatening infection.
Children who have had the chickenpox vaccine can still get chickenpox. However, they usually have a much milder case with a smaller number of blisters.
Cellulitis (a skin infection from bacteria) is by far the most common complication in children. It may leave scarring, especially if the child scratches the lesions. Necrotizing fasciitis ("flesh-eating disease") in children, though extremely rare, can occur as a complication of infection entering through the chickenpox lesions. An awkward problem occurs when chickenpox blisters appear in the mouth, throat, or anus. Lesions in these places are very uncomfortable. If the rash gets near the eyes, consult your doctor.
Like many viruses, the varicella-zoster virus is never completely gone once it has entered your body. Anyone who's had chickenpox carries dormant viruses in the roots of their nerve cells. These can sometimes reappear years later as shingles, a painful skin rash that affects a particular area of skin.
Shingles can appear at times of emotional stress, or when the immune system is low. It's not always known what has provoked the virus to come out of hiding. It's important to know that the shingles rash can transmit chickenpox. People who have already had chickenpox are immune, but people who haven't can get it from other people's shingles.