Skin infection is the most common complication of chickenpox. Skin infections occur when bacteria from your skin or under your fingernails get into a chickenpox blister. Sometimes a skin infection from chickenpox can be serious.

Other complications of chickenpox are rare. They include:

• Varicella pneumonia. Pneumonia can develop if the chickenpox virus travels to your lungs. Pneumonia from chickenpox is most common in teens, adults, and pregnant women who have chickenpox in the last part of pregnancy. It is also more likely to develop in people who smoke cigarettes, have lifelong (chronic) lung diseases, or have impaired immune systems.
• Inflammation (swelling) of the brain, known as encephalitis. Encephalitis can develop about 5 to 10 days after the chickenpox rash appears. In children, encephalitis most often affects a specific part of the brain (cerebellum) and is called acute cerebellar ataxia. It mainly causes poor muscle coordination, although other symptoms of encephalitis can also occur. In adults, this complication is more likely to affect a bigger part of the brain and cause more severe symptoms. Encephalitis symptoms include confusion, a high fever, a severe headache, sleepiness, sensitivity to light, and nausea. In the most serious cases, a person may have seizures or tremors. Treatment may include medication to help relieve symptoms. Some people with encephalitis may need to stay in the hospital.
• Vision loss. Chickenpox virus that spreads into the clear eye covering (cornea) can leave scars that can cause vision loss.
• Reye's syndrome. Reye's syndrome can develop in young people who take aspirin during chickenpox or flu treatment. It can be prevented by not giving aspirin to anyone under the age of 20.
• Inflammation of the joints (arthritis). Sometimes people with chickenpox have pain in their muscles and joints. This pain usually lasts as long as the chickenpox rash. Medications taken for fever or other general illness often help ease the pain.

The following complications of chickenpox are very rare:

• Inflammation of the nerves of the eye (optic neuritis) or the spinal cord.
• Inflammation of the tissues surrounding the brain and spinal cord (meningitis).
• Nerve damage that causes problems with movement of the face or other parts of the body.
• Certain blood disorders, such as a decrease in the number of blood cells that help clot blood (thrombocytopenia).
• Death. Before introduction of the chickenpox vaccine in the United States in 1995, about 100 people died each year from chickenpox.¹

Women who are pregnant when they have chickenpox are at risk of complications such as premature labor or varicella pneumonia, and the fetus is at risk of developing chickenpox. Fetuses with chickenpox are more likely to develop birth defects or other complications before and after birth. Newborn babies can also get chickenpox when their mother has the illness within a few days of delivery.