Reye's syndrome is a rare illness that can be life threatening. The illness occurs mainly in young children and usually follows a viral infection, such as the flu, chicken pox, or upper respiratory infection. It occurs most often in children between the ages of 2 and 16 years.
The exact cause of Reye's Syndrome is unknown. It is believed that aspirin use may trigger its development in children. This is why children younger than 18 years of age should not be given aspirin for any reason.