Reye (pronounced “rye”) syndrome is a rare, potentially life-threatening illness. It primarily affects the brain and liver, causing inflammation and pressure inside the head (with corresponding cognitive or behavioral symptoms) and dysfunction of the liver, leading to a dangerous buildup of toxins in the body.

Reye syndrome occurs almost exclusively in children and teenagers recovering from viral illnesses such as a cold, the flu or chickenpox. The use of aspirin or aspirin-containing medication (presumably to treat the viral infection) has been associated with onset of the syndrome.

People of all ages may be affected, but Reye syndrome occurs most often among those under 15 years old. Nearly half of all reported cases have occurred in children under 5 years old, according to the Centers for Disease Control and Prevention (CDC). It is estimated to occur in 1 out of every 100,000 children under the age of 18.

The syndrome is named after an Australian pathologist, Dr. R. Douglas Reye, who along with North Carolina physician George Johnson, published the first study of the syndrome in 1963. Outbreaks of Reye syndrome occurred in the United States during the 1960s and 1970s. Since the early 1980s, the number of cases reported has dropped dramatically. This may be related to increased publicity during the early 1980s warning people about the danger of using aspirin and aspirin-containing medication in children. In addition, several other conditions known as inborn errors of metabolism have since been identified that have symptoms similar to Reye syndrome. Some earlier suspected Reye syndrome cases actually may have been these metabolic conditions.

In 1982, the surgeon general advised against use of these medications in children with influenza or chickenpox. In 1986, the Food and Drug Administration (FDA) ruled that all over-the-counter aspirin and aspirin-containing products must carry a warning label about Reye syndrome. Another warning stating that children and teenagers who have chicken pox or flu symptoms, or are recovering from these illnesses, should not use aspirin became effective in 2004.

Reye syndrome primarily affects the brain and liver. It causes swelling and accumulation of fat in the liver. The liver fails to function as it should, and may cause poor blood clotting and increased bleeding. Patients with Reye syndrome tend to have high levels of ammonia and acidity in their blood and low levels of blood sugar (glucose). 

Reye syndrome may cause brain damage due to accumulation of fluids in the brain, which causes the brain to swell and pressure in the head to increase. This can result in life-threatening seizures, coma and brain damage. Reye syndrome may also affect other organs in the body.

The death rate among patients with Reye syndrome was initially 40 percent, but has decreased to between 20 and 30 percent of reported cases, according to the CDC. Most children with Reye syndrome survive and many have no long-terms complications.