Complications of chickenpox are rare in healthy children. The most common complication is where the blisters become infected with bacteria.

A sign that the blisters have become infected is when the surrounding skin becomes red and sore.

If you think that your child's blisters have become infected, contact your GP as the child may need a course of antibiotics.

Other complications in children

Very rarely, chickenpox can lead to more serious complications involving the nervous system (brain and spinal cord) in children.

These include infections of the brain (encephalitis), the protective membranes around the brain (meningitis) or part of the brain called the cerebellum (cerebellitis).

Signs of these problems can include:

• a lack of energy
• drowsiness
• confusion
• seizures (fits)
• vomiting
• severe headaches
• a stiff neck
• behavioural changes
• problems with walking, balance or speech (ataxia)

Seek medical advice as soon as possible if your child develops any of these symptoms after having chickenpox.

At-risk groups

The people who are most at risk of developing chickenpox complications are:

• adults
• pregnant women
• babies under four weeks old
• people with a weakened immune system 

Adults

Chickenpox can be more serious in adults than in children. Adults with the virus are more likely to be admitted into hospital. Approximately 5-14% of adults with chickenpox develop lung problems, such as pneumonia. If you smoke, your risk of developing lung problems is much higher.

Although it is more serious in adults, most people will still make a full recovery from the chickenpox virus.

Pregnant women

If you're pregnant, chickenpox can occasionally cause complications.

For example, your risk of developing pneumonia is slightly higher if you're pregnant, especially if you smoke. The further you are into your pregnancy, the more serious the risk of pneumonia tends to be.

If you get chickenpox while you're pregnant, there is also a small but significant risk to your unborn baby.  

If you are infected with chickenpox during the first 28 weeks of your pregnancy, there is a risk that your unborn baby could develop a condition known as foetal varicella syndrome (FVS).

This syndrome is rare. The risk of it occurring in the first 12 weeks of pregnancy is less than 1%. Between weeks 13 and 20, the risk is 2%.

There have only been a few reports of FVS due to an infection from weeks 20 to 28 of pregnancy, and the risk is thought to be much less than 1%.

FVS can cause serious complications, including:

• scarring 
• eye defects, such as cataracts
• shortened limbs
• brain damage

There are also other risks from catching chickenpox after week 20 of pregnancy.

It's possible that your baby may be born prematurely (before week 37 of the pregnancy).

If you are infected with chickenpox seven days before or seven days after giving birth, your newborn baby may develop a more serious type of chickenpox. In a few severe cases, this type of chickenpox can be fatal.

See your GP urgently if you're pregnant or have given birth in the last seven days and you think you may have chickenpox, or if you've been exposed to someone who has chickenpox.

People with a weakened immune system

Your immune system is your body's way of defending itself against disease, bacteria and viruses.

If your immune system is weak or does not work properly, you are more susceptible to developing infections such as chickenpox. This is because your body produces fewer antibodies to fight off the infection.

You may have a weakened immune system if you take immunosuppressive medication.

Immunosuppressive medication such as steroid tablets may be used if, for example, you have an inflammatory condition such as rheumatoid arthritis, lupus or certain blood conditions.

If you have a weakened immune system, you're also more at risk of developing complications from chickenpox. These complications include:

• pneumonia
• blood poisoning (septicaemia)
• meningitis

See your GP urgently if you have a weakened immune system and you've been exposed to the chickenpox virus.

For more information, read about how to stop the spread of chickenpox.