Patient Basics: Reye Syndrome

Reye syndrome (also called Reye’s syndrome) is a rare but very serious illness that causes swelling in the brain and damage to the liver. It mostly affects children and teens who are getting over the flu, chickenpox or another virus, and it is strongly linked to taking aspirin while sick. To help prevent it, don’t give aspirin to anyone under 19 unless a doctor tells you to.

Key points

• Reye syndrome usually starts a few days after a flu-like illness or chickenpox, just as the child seems to be getting better.
• Repeated vomiting followed by sleepiness, confusion or unusual behavior are warning signs. Get emergency care right away.
• There is no cure, but early treatment in an intensive care unit gives the best chance of full recovery.
• Aspirin and related drugs called salicylates are found in some products you might not expect, so read labels.
• Since warnings about aspirin began in the 1980s, Reye syndrome has become very rare in the US.

What causes Reye syndrome

Doctors don’t fully understand the cause. It seems to happen when a viral infection and aspirin together damage mitochondria, the tiny energy factories inside cells. In the liver, fat builds up and the liver can’t clear ammonia and other waste from the blood. The brain swells, and pressure inside the skull rises.

The viruses most often involved are influenza (flu) and chickenpox (varicella). Stomach viruses and colds have also been linked to it.

Some inherited conditions that affect how the body breaks down fat (fatty acid oxidation disorders) can cause a very similar illness. Doctors often test for these, especially in babies and young children, or when a child has had repeated episodes.

Reye syndrome symptoms

Symptoms usually start 3 to 5 days after the first signs of the virus. They can get worse within hours.

Early signs:

• Vomiting that is heavy and keeps happening
• Unusual sleepiness or lack of energy
• Irritability, aggressive behavior or acting out of character
• In babies, diarrhea and fast breathing may come in place of vomiting

Later signs:

• Confusion, not knowing where they are, or seeing things that aren’t there
• Weakness or trouble moving the arms or legs
• Seizures
• Extreme drowsiness, passing out or coma

Call 911 or go to an emergency department right away if a child or teen has these signs, especially after the flu or chickenpox. Tell the team about every medicine the child took, including any that might contain aspirin.

How it’s diagnosed

There is no single test for Reye syndrome. Doctors put together the history and test results, and rule out other causes such as meningitis, encephalitis, poisoning and inherited metabolic disorders.

• Blood tests often show high liver enzymes, high ammonia, low blood sugar and slow blood clotting.
• A spinal tap (lumbar puncture) checks the fluid around the brain and spinal cord for infection.
• A CT scan or MRI of the head looks for brain swelling and other causes.
• Other tests may screen for metabolic disorders. A liver biopsy is rarely needed.

How Reye syndrome is treated

Treatment happens in a hospital, usually in a pediatric intensive care unit. The aim is to protect the brain and support the body while the liver recovers.

• Fluids through a vein (IV) with sugar and salts to correct low blood sugar and imbalances
• Medicines to lower pressure in the brain, and keeping the head raised
• A breathing machine (ventilator) if breathing is affected
• Vitamin K or plasma to help the blood clot
• Medicines to prevent or stop seizures
• Close checks of heart rate, blood pressure, breathing and brain pressure

Recovery

How well a child recovers depends mostly on the amount of brain swelling. Children diagnosed and treated early often recover fully. Severe cases can cause lasting problems with attention, memory, speech, movement or learning, and some cases are fatal. Children who had brain effects may need rehabilitation and school support afterward.

Preventing Reye syndrome

• Don’t give aspirin to children or teens under 19, especially during a fever or viral illness, unless a doctor prescribes it for a specific condition.
• Read labels. Look for aspirin, acetylsalicylic acid, salicylate, salicylic acid, bismuth subsalicylate and oil of wintergreen (methyl salicylate). Some stomach remedies, cold medicines and pain rubs contain these.
• Use other medicine for fever and pain. Acetaminophen or ibuprofen are used for children instead. Ibuprofen is for babies 6 months and older. Follow the dose on the label for your child’s weight or age.
• Get vaccinated. Yearly flu shots and the chickenpox vaccine lower the chance of the infections that can lead to Reye syndrome.
• If your child must take aspirin long term, for example for Kawasaki disease or a heart condition, ask the doctor what to do if they catch the flu or chickenpox, and make sure their vaccines are up to date.

Common questions about Reye syndrome

Can adults get Reye syndrome?

It is very rare in adults, but it has been reported. Nearly all cases are in children and teens. Adults who take aspirin during a viral illness have a very low risk. Still, any adult with confusion and repeated vomiting after the flu needs urgent medical care.

Is Reye syndrome contagious?

No. Reye syndrome itself doesn’t spread from person to person. The viruses that come before it, such as flu and chickenpox, are contagious. Vaccines, handwashing and keeping sick children home help prevent those infections. If a brother or sister catches the same virus, treat their fever with acetaminophen or ibuprofen, never aspirin.

Can children take Pepto-Bismol?

Regular Pepto-Bismol contains bismuth subsalicylate, a chemical related to aspirin. Children and teens should not take it during or after the flu or chickenpox, and the regular product is labeled only for ages 12 and up. Ask a pharmacist about other choices for a child’s upset stomach.

How common is Reye syndrome today?

Very rare. In the US, cases dropped from several hundred a year around 1980 to very few a year today. The drop followed public warnings and label changes on aspirin for children. Because it is so uncommon, doctors may not think of it at first, so mention any aspirin use.

Questions to ask your doctor

• Which fever and pain medicines can my child take, and how much?
• Which products should I avoid because they contain salicylates?
• Is my child up to date on flu and chickenpox vaccines?
• Should my child be tested for a metabolic disorder?
• What follow-up care will my child need after recovering?

Learn more

• Reye’s syndrome (National Institute of Neurological Disorders and Stroke)
• Reye syndrome (MedlinePlus, U.S. National Library of Medicine)

This guide is general information and doesn’t replace advice from your own doctor. Last updated October 2026.