Reye (RYE) syndrome is a rare but potentially fatal illness of preschool and school-age children. It usually occurs between ages three and 12 and causes liver damage and swelling of the brain, which can lead to permanent brain damage. Its exact cause isn't known, but it always occurs in someone who's had a viral infection, such as chicken pox or the flu. There are theories as to what causes it, such as reactions to medication, especially aspirin, given during the illness; a toxin released while the child is sick; or some chemical changes in the body of a susceptible child caused by the illness. When some children have a viral infection, they may exhibit signs of having contracted (con-TRAC-ted) Reye syndrome if they gradually improve, then go into sudden, repeated vomiting over a 36-hour period. The child also may seem irritable, confused, and lethargic. Children with Reye syndrome must be hospitalized. As a precaution, never give a child aspirin, and check labels of products to make sure they don't contain aspirin. If you must give a child medication, make sure it's a pain reliever that's been approved by a doctor.