Chickenpox is a very contagious disease caused by a virus (varicella zoster virus), and can be very serious for babies, pregnant women and people with weakened immune systems.

The virus that causes chickenpox is spread by coughing and sneezing, and also by contact with chickenpox blisters. Infected people are contagious for 1-2 days before the rash appears, and can spread the infection until all of the blisters have formed scabs. People with shingles (a disease caused by the same virus) can also spread the chickenpox virus.

The first signs of chickenpox will appear in your child between 10 and 21 days after infection. Usually he will develop a fever, headache, loss of appetite, tiredness, and the characteristic rash. The rash goes through three phases- firstly raised pink or red bumps, then fluid-filled blisters that form over the red bumps (these break and leak after a day or two), and then finally crusts and scabs that cover the blisters. The whole process happens gradually over several days.

Chickenpox is usually a mild disease but there can be complications – commonly, blisters can become infected with bacteria and antibiotics will be needed to get rid of the infection. Other complications can include bacterial infections (of the soft tissues, bones, joints or the blood), pneumonia, encephalitis (swelling of the brain), toxic shock syndrome (serious bacterial infection), and Reye’s syndrome.

Reye’s syndrome is a swelling in the brain and liver that can be fatal; it is sometimes linked to children taking aspirin when they have chickenpox. Signs that your child might be developing these complications include a lack of energy, drowsiness, confusion, seizures, vomiting, severe headaches, a stiff neck, behavioural changes and problems walking or with balance or speech. See your doctor immediately if you notice any of these symptoms.

Chickenpox can be very serious for pregnant women; if you are infected during the first 28 weeks of pregnancy there is a small risk of the unborn baby developing foetal varicella syndrome (FVS). FVS can cause scarring, eye defects, shortened limbs and brain damage. If you are infected 7 days before or after giving birth your newborn is at risk of serious disease and even death – if you are pregnant or have recently given birth and you have been in contact with someone who has chickenpox, contact your doctor immediately.

Shingles can happen in some people years after getting chickenpox; this is caused by the virus being stored in the nerves and then causing painful blisters on the skin if their immune system can’t control the infection.

Chickenpox is usually a mild disease that healthy adults and children recover from. It can cause serious complications in some people, including young babies, pregnant women, adults and people with weakened immune systems. Newborn babies are at risk of dying if they are exposed to the disease. The chickenpox (varicella) vaccine protects children from the virus that causes chickenpox.