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About chickenpox


What is a chickenpox?

Chickenpox or varicella is a viral infection that can be easily passed from person to person. A person with chickenpox is contagious from one to two days before the rash appears until all the rash has crusted over. It can be a very serious illness in a child with an immune system that has been weakened by cancer therapy or other immune problems. The virus usually causes fever, loss of appetite, and decreased activity followed by an itchy rash. In children with weakened immune system, it may progress to infect other organs including brain, lungs, and liver.

What does it look like?

It takes 10 to 21 days from the time the child is exposed before you will begin to see the pox (rash).

The chickenpox rash usually appears first on the trunk and face, and then it spreads to almost everywhere else on the body, including the scalp and groin, and inside the mouth, nose, and ears.

At first, the rash looks like pinkish dots that quickly develop a small blister on top (a blister is a bump on the skin that fills up with fluid). After about 24 hours, the fluid in the blisters gets cloudy and the blisters begin to break open and crust over.

How long will it last?

Chickenpox blisters show up in waves, so after some have broken open, a new group of spots may appear. Typically, new chickenpox blisters usually stop appearing by the third day, and by the sixth day, all the blisters should have scabs on them and start to heal. In children who have a weakened immune system, the rash is usually more severe and will last longer than 3–6 days. This happens because the child is not able to fight the virus as well as a healthy child.

The illness cannot be passed to others after the blisters have completely dried and healed. Children are usually "immune to" (protected from) chickenpox after having the illness although the virus remains present in the body.

What is shingles?

Shingles is another illness caused by the varicella virus. The child who has had chickenpox is at risk for developing shingles because the virus remains present in body and can move back down nerves to the skin.

Although it is more common in adults, anyone who has had chickenpox is at risk for developing shingles. Shingles is also more common in people with weakened immune systems from HIV infection, chemotherapy, radiation treatments, transplant operations, and stress.

What about the vaccine?

The chickenpox (or varicella) vaccine is now recommended for all children in the United States. It is a weakened form of the virus that causes very little disease but protects against the more dangerous natural form of the virus. Children who have had the chickenpox shot rarely develop actual chickenpox, even if their immune systems are weakened. Because the weakened virus remains in the body just like the natural form, persons who have had the shot can also get shingles later in life, although it is rare. Chickenpox vaccine should not be given to children with weakened immune system because it contains weakened live virus. It is important that the siblings of a child with weakened immune system receive the chickenpox vaccine to protect them from getting the infection and thus indirectly protecting the child with weakened immune system.

Being around someone (brother, sister, friend) with chickenpox or shingles is a danger to the child with a weak immune system who has never had chickenpox or has never had the chickenpox vaccine. The child's doctor should be told right away if the child comes in contact with someone who has chickenpox or if the child was exposed 2 days before the other child developed the chickenpox rash.

If the child has been exposed and has never had chickenpox or the chickenpox vaccine, your doctor may recommend medicine for chickenpox or may give a treatment that contains antibodies against the chickenpox virus. Children who have been exposed to chickenpox must stay apart from other children with weakened immune systems for several weeks to make sure they do not pass the virus on to another child.

Your hometown doctor, nurse, school teachers, and parents of friends should be told about the danger of chickenpox to your child.

When to call the doctor

If your child has a weak immune system, call his doctor if you find blisters or a rash on your child. Call your hometown doctor or St. Jude Children's Research Hospital right away, day or night.

Also call your child’s St. Jude doctor right away, if your child has never had chickenpox or the chickenpox vaccine and is exposed to someone with chickenpox or shingles. This staff member can help you decide if the exposure is cause for alarm. See “Do you know… The Signs of Infection” for more details about when you should call your child’s doctor.

Important message

Many St. Jude patients are at increased risk of infection. If your child has a rash, has been exposed to chickenpox or shingles, or has any infection that could be passed to other patients, such as a virus or diarrhea, the condition needs to be checked before you allow your child to be near other St. Jude patients. Please call the hospital switchboard at 901-595-3300 and ask for the nursing coordinator; from outside Memphis, dial toll-free 1-866-2ST-JUDE. St. Jude staff will make special plans:

  • For your child to be seen in one of the clinic isolation rooms;
  • For private transportation and entrance to the hospital, so other patients are not exposed to a contagious illness; and
  • For you to stay at a hotel where your child will not be around other patients.
  • The doctor and nurse will wear masks, gowns, and gloves when they examine your child.

If you have questions about your child’s risk of infection, talk to your child’s doctor or nurse.


This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

ATTENTION: If you speak another language, assistance services, free of charge, are available to you. Call 1-866-278-5833 (TTY: 1-901-595-1040).

ATENCIÓN: si habla español, tiene a su disposición servicios gratuitos de asistencia lingüística. Llame al 1-866-278-5833 (TTY: 1-901-595-1040).

تنبيه: إذا كنت تتحدث باللغة العربية فيمكنك الاستعانة بخدمات المساعدة اللغوية المتوفرة لك مجانا. .يرجى الاتصال بالرقم. 5833-278-866-1  (الهاتف النصي: 1040-595-901-1).