What Is It?
Chickenpox is an infection that causes an itchy, blistering rash and is very contagious, meaning it is spread easily from one person to another. It is caused by varicella-zoster virus (VZV), which enters the body through the mouth and nose after contact with an infected person.
A person with chickenpox can spread the disease to someone else from one day before the rash appears until all chickenpox blisters have crusted over. Once someone has had a chickenpox infection, he or she almost always develops a lifelong immunity, meaning that person usually does not get chickenpox a second time. The exception is a child who is infected at a very young age. Young children usually have milder cases and may not build up enough protection against the disease. Therefore, these children may develop the disease again later in life.
Because chickenpox is so contagious, 90 percent of a patient's family also will develop the illness if they live in the same house and are not already immune. In the past, chickenpox cases often occurred in groups (epidemics), usually during the late winter and early spring. However, the number of cases of chickenpox has dropped dramatically because of the chickenpox (varicella) vaccine, which was licensed in 1995 and is recommended for all children.