Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Febrile Seizures

What Is It?

Febrile seizures occur in children. They are caused by a high fever or by a sudden rise in body temperature. These seizures usually happen at the beginning of an illness, soon after the fever first starts. Febrile seizures affect about 3 percent of children. They are most common between ages 6 months and 5 years.

What is a seizure? The brain's nerve cells (neurons) communicate with each other by giving off tiny electric signals. When someone has a seizure (convulsion), the way the brain's nerve cells give off signals suddenly changes, causing different muscles in the body to twitch or jerk uncontrollably.

More than one in three children who have had a febrile seizure will have another one within one year, but most children eventually grow out of this condition. The risk of having another seizure is greater in children with a family history of febrile seizures, and in children who had their first seizure when they were younger than 12 months old. Children who have delays in normal development are also more likely to have seizures with fever.