For healthy babies, chicken pox is usually more of a nuisance than a real threat. On rare occasions, though, even healthy children can develop serious complications from chicken pox, like a bacterial skin infection, pneumonia, or encephalitis, a swelling of the brain.
If your child has chicken pox, call the doctor if she seems sicker than expected, if she develops a fever after the first few days, if the rash spreads to her eyes, or if the skin around the pox becomes swollen, painful, or very red.
If your child has a weakened immune system from a chronic illness such as leukemia or from taking high-dose oral steroids (for asthma, for example), the infection can cause grave complications. Some special protective measures, such as an injection of varicella zoster immune globulin or the varicella vaccine, can only be useful shortly after exposure. If your baby's immune system is compromised, call her doctor at the first sign of chicken pox — or even if she's only been exposed to someone who's sick.
Adults who come down with chicken pox can get very sick and are at risk for such complications as bacterial pneumonia. If you're pregnant and have never had chicken pox, read our article on chicken pox during pregnancy and ask your doctor what precautions you should take and what to do if you've been exposed.