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What is chickenpox? Chickenpox is an illness caused by the varicella-zoster virus. It is most common in young children but older children and adults who have never had chickenpox can be sick with it as well.


  • Front of chickenpox fact sheetChickenpox Fact Sheet (PDF)
    View, download and print the Chickenpox Fact Sheet. Chickenpox is an illness caused by the varicella-zoster virus. It is most common in young children but older children and adults who have never had chickenpox can be sick with it as well.

Table of Contents

What are the signs and symptoms of chickenpox?

  • Chickenpox may begin with a mild fever, followed in a day or two by a rash, which may be very itchy.
  • The rash starts with red spots that soon turn into fluid-filled blisters. These blisters then open, the fluid dries and crusts form over the blisters.
  • It takes 14-21 days from the time the virus gets into the body before symptoms start to show.

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For more information, please contact the Infectious Disease Control Team:

  • 519-663-5317 Ext. 2330

How is chickenpox spread?

  • Chickenpox is spread very easily through the air or through contact with the fluid from a chickenpox blister.
  • It can be spread from a pregnant woman to her baby before she gives birth.
  • It spreads easily among people who have never had chickenpox and can spread within childcare centers, schools and families.
  • Chickenpox is contagious one to possibly five days before the rash starts. A person can continue to spread it to others for up to five days from when the rash begins or until all the blisters have crusted over, whichever comes first.

When can children with chickenpox return to childcare or school?

  • Children can return to school or childcare if they feel well enough to participate in all activities even if they still have a rash.


  • People with chickenpox usually get better on their own. Medical treatment for chickenpox is usually not needed.
  • Never give aspirin (acetylsalicylic acid-ASA) or any medicine that contains aspirin to a person who is sick with chickenpox. Aspirin can increase the risk of a severe illness called Reye’s syndrome in people with chickenpox and other viral illnesses. To control fever, use acetaminophen (Tylenol®, Tempra®).
  • For people with a high risk of complications, doctors sometimes prescribe medications to shorten the length of illness. If complications do develop, the doctor will determine the appropriate treatment.
  • Calamine lotion may help with the itching. Keep fingernails short to prevent scratching and scarring.


  • The most effective way to prevent chickenpox is through the chickenpox (varicella) vaccine, known as Varivax III® or Varilrix®. Additional details can be found on our Immunization page.
  • Chickenpox vaccine should NOT be used in pregnancy.

Chickenpox and pregnancy

Pregnant women who become infected with chickenpox can develop severe disease. Infection during pregnancy may lead to problems for the baby.

  • If you are pregnant, have been in contact with someone who has chickenpox, and are unsure if you have had chickenpox, talk to your doctor as soon as possible after the exposure.
  • A blood test can be done to see if you have protection against chickenpox. Depending on the blood test result, there may be further follow-up with your doctor.

For additional information, please see the Middlesex-London Health Unit's fact sheet chickenpox and pregnancy.


  • Anyone who has had chickenpox is at risk of an illness called shingles (also known as herpes zoster). After being sick with chickenpox, the chickenpox virus stays in your body for life. Many years later, the virus can come back as shingles.
  • Shingles causes a painful area of blisters, usually on one part of the body.
  • Shingles cannot be passed from one person to another. However, the virus that causes shingles, can spread from a person with active shingles to cause chickenpox in someone who had never had chickenpox or received chickenpox vaccine.
  • The virus is spread through direct contact with the fluid-filled blisters of someone with Shingles. A person with active sores can spread the virus to others for a week after the blister-like rash begins.
  • A person with shingles can remain at school or work if the blisters are covered. Shingles is not spread through the air.
  • There is a medication your doctor may prescribe that can lessen the severity of the illness.
Date of creation: November 24, 2012
Last modified on: January 29, 2024


1Canadian Pediatric Society. Caring for Kids (2011). Chickenpox Retrieved from
2Heymann, D. L. (2015). Control of communicable diseases manual (20th ed,). Washington, DC: American Public Health Association.
3Pickering, L.K., Baker, C.J, Kimberlin, D.W., & Long, S.S. (Eds.). (2012). Red book 2012: Report of the committee on infectious diseases (28th ed.). Elk Grove Village, Ill: American Academy of Pediatrics.