Reye’s syndrome is a rare but serious illness that causes sudden brain swelling and a dangerous buildup of fat in the liver, most often in children and teenagers recovering from a viral infection such as the flu or chickenpox. What makes it unusual, and largely preventable, is its strong link to aspirin: taking aspirin or other salicylate medicines during a viral illness in a young person sharply raises the risk. Public-health warnings in the 1980s made avoiding aspirin routine, and cases have since become very rare. This guide explains what Reye’s syndrome is, how to recognize its warning signs, why aspirin matters, how doctors diagnose it with blood tests, and what current treatment, prevention, and research have to offer.
What is Reye’s syndrome?
Reye’s syndrome damages two organs at once: the brain, where it causes acute swelling known as encephalopathy, and the liver, where fat accumulates in the cells and normal function breaks down. It was first described in 1963 by the Australian pathologist R.D.K. Reye and drew intense attention in later decades when doctors linked it to aspirin given during common childhood infections. The illness is not an infection itself and does not spread from person to person; it appears to be a rare reaction in a small number of susceptible children after an ordinary virus.
The timing is one of its most recognizable features. Reye’s syndrome follows a biphasic course, striking in two waves: a child catches a virus and begins to get better, and then, usually within a few days to a week, a second and far more dangerous phase begins with relentless vomiting and rapidly changing behavior. Because both organs are affected, the blood chemistry shifts in ways a laboratory can detect early, which is central to how the diagnosis is made.
Symptoms of Reye’s syndrome
The warning signs typically appear three to seven days after a viral infection, often just as the child seems to be improving. The first and most consistent symptom is persistent vomiting that does not settle, followed by changes in alertness and behavior as the brain begins to swell. In very young children the picture can differ, with diarrhea and rapid breathing rather than vomiting. Reye’s syndrome does not usually cause a rash of its own; when a rash is present, it generally belongs to the preceding chickenpox.
As the condition advances, the neurological symptoms become more alarming. A child may grow unusually sleepy and hard to rouse, then irritable, confused, or combative, and can progress to seizures, loss of consciousness, and coma if the illness is not treated quickly. Any child who develops repeated vomiting and a change in behavior while recovering from a viral illness needs urgent medical assessment.
| Stage | Typical signs |
|---|---|
| Early symptoms | Persistent vomiting that will not stop; in infants, diarrhea and fast breathing instead |
| Behavioral changes | Unusual sleepiness and lethargy, followed by irritability, confusion, or aggressive behavior |
| Advancing signs | Disorientation, hallucinations, and weakness in the arms and legs |
| Severe stage | Seizures, loss of consciousness, and coma, which are medical emergencies |
Causes and risk factors: the aspirin connection
The central risk factor for Reye’s syndrome is taking aspirin or other salicylate-containing medicines during a viral illness in childhood or the teenage years. The exact mechanism is still not fully understood, but the statistical link is strong enough that health authorities changed medical practice around it. The infections most often involved are influenza and chickenpox, which is why it helps to read the flu symptoms, causes, and treatment options and to review the chickenpox symptoms, causes, treatments, and prevention guide.
Because of this link, aspirin is generally not recommended for anyone under about 19 with a viral infection, and acetaminophen or ibuprofen are the usual alternatives. Salicylates hide in more products than people expect, including some bismuth subsalicylate stomach remedies and certain cold preparations, so reading medicine labels matters. One exception is that a small number of children take daily low-dose aspirin for specific heart or rheumatic conditions, such as Kawasaki disease; those children are managed carefully by their own doctors, who advise families on what to do during viral illnesses.
Reye’s syndrome and inborn errors of metabolism
A key development in understanding this condition is the recognition that many children who appear to have Reye’s syndrome actually have an underlying inherited metabolic disorder. These conditions, called inborn errors of metabolism, interfere with how the body breaks down fats or clears toxins, and a common viral illness can push them into a crisis that looks almost identical to classic Reye’s syndrome. A well-known example is a group of fatty-acid oxidation disorders that includes medium-chain acyl-CoA dehydrogenase deficiency, or MCAD deficiency.
This overlap is why doctors now test to exclude metabolic conditions whenever a child presents with a Reye-like illness. Because a struggling liver leaks enzymes into the blood in both situations, these children often show elevated liver enzymes, and it can help to see what alanine aminotransferase (ALT) reveals about the liver. Identifying an inborn error of metabolism changes treatment and long-term care, and in many places newborn screening now catches some of these disorders before a crisis ever occurs.
How Reye’s syndrome is diagnosed
Because the early symptoms overlap with many childhood illnesses, laboratory testing is central to recognizing Reye’s syndrome, and the blood results follow a distinctive pattern. Liver enzymes rise sharply as liver cells are injured, so clinicians may review how aspartate aminotransferase (AST) levels are interpreted. A markedly high blood ammonia level is one of the most telling findings, and it helps to understand what a high ammonia level means on a blood test. Blood sugar often falls at the same time and clotting slows, so doctors measure prothrombin time; you can review what prothrombin time reveals about blood clotting.
A revealing detail is what is usually missing: despite the liver injury, children with Reye’s syndrome typically do not turn yellow, because bilirubin often stays within its normal range, and in this condition you can read why the total bilirubin level usually stays normal. To rule out other causes, doctors may add brain imaging with a CT or MRI scan, a spinal tap to exclude infections such as meningitis, and metabolic testing for an inborn error of metabolism. In some cases a liver biopsy is performed, which shows the tiny fat droplets, called microvesicular steatosis, that are characteristic of the condition.
| Test | What it typically shows in Reye’s syndrome |
|---|---|
| Liver enzymes (AST and ALT) | Elevated, reflecting injury to liver cells |
| Blood ammonia | Markedly high, a hallmark of the disrupted liver metabolism |
| Blood glucose | Often low (hypoglycemia), especially in younger children |
| Prothrombin time | Prolonged, showing that clotting is impaired |
| Bilirubin | Usually normal, so jaundice is typically absent |
| Liver biopsy | Microvesicular fatty change, when a biopsy is needed to confirm |
Treatment and recovery
There is no specific cure for Reye’s syndrome, so treatment is supportive and urgent, given in a hospital and usually an intensive care unit. The central goal is to protect the brain while the body recovers, which means controlling the raised pressure inside the skull that comes from cerebral edema, the swelling that makes the condition so dangerous. Care teams also correct the metabolic problems the blood tests reveal, giving intravenous fluids and glucose to steady blood sugar, and it can help to learn how blood glucose test results are read.
Doctors also correct clotting problems, sometimes with vitamin K or plasma products, and use medications and positioning to ease pressure on the brain. Children whose breathing or consciousness is failing may need a breathing tube and mechanical ventilation. The most important factor in recovery is time: early recognition and prompt hospital treatment substantially improve the odds, which is why any suspicion of Reye’s syndrome should be treated as an emergency rather than watched at home.
Prevention
Reye’s syndrome is one of the few serious childhood illnesses that is largely preventable, and prevention comes down to a few clear habits. The most important is avoiding aspirin and other salicylate products in children and teenagers who have a viral infection, and choosing acetaminophen or ibuprofen instead when a fever reducer is needed. Reading the ingredient list on over-the-counter medicines matters too, because salicylates can appear under names such as acetylsalicylic acid or bismuth subsalicylate rather than the word aspirin.
- Do not give aspirin or salicylate products to anyone under about 19 during a viral illness unless a doctor has specifically prescribed it.
- Use acetaminophen or ibuprofen for fever and aches in children, following the dosing directions for their age and weight.
- Check the labels of cold, flu, and stomach remedies for hidden salicylates, including bismuth subsalicylate.
- Keep routine vaccinations up to date, including the influenza and chickenpox vaccines, to reduce the viral infections that can precede Reye’s syndrome.
- If your child takes daily aspirin for a diagnosed condition, ask their doctor in advance what to do when they catch a virus.
Complications and long-term outlook
The most dangerous complication is the brain swelling itself, which can lead to seizures, coma, permanent neurological damage, and, in the most severe cases, death. Outcomes have improved as recognition and intensive care have advanced, and many children treated early recover completely with no lasting effects. Others are left with problems that reflect the degree of brain injury, from mild difficulties with attention or coordination to more significant intellectual or physical disability.
The strongest predictor of a good outcome is how quickly the illness is recognized and treatment begins, before the brain swelling reaches its most severe stage. Because Reye’s syndrome can move quickly, the practical message for families is the same one the diagnosis rests on: relentless vomiting and confusion in a child recovering from a virus is a reason to seek emergency care without delay.
Latest scientific advances in Reye’s syndrome research
Reye’s syndrome is now so rare that large new clinical trials are uncommon, and much of the recent literature focuses on recognizing it correctly rather than on new cures. A 2025 review examined adult-onset Reye’s syndrome and whether people who had the illness as children can later take low-dose aspirin safely; it found the older evidence thin and often unconfirmed, and called for better-documented studies before firm advice can be given (Gibson et al., 2025). What this means for you: Reye’s syndrome is overwhelmingly a childhood illness, and if you have a personal history of it, decisions about aspirin as an adult should be made individually with your doctor rather than from general rules.
Other recent work sharpens the line between true Reye’s syndrome and the metabolic disorders that imitate it. A 2025 report on a national newborn screening program described how tandem mass spectrometry detects MCAD deficiency, a fatty-acid oxidation disorder that can cause a Reye-like crisis of low blood sugar and encephalopathy, so that many affected infants are identified before they ever become ill (Glab-Jablonska et al., 2025). What this means for you: some children once labeled as having Reye’s syndrome actually have a treatable inherited condition, and modern screening increasingly catches these disorders early, which changes both treatment and family planning.
Researchers also continue to re-examine when aspirin is genuinely unsafe in children. A 2026 narrative review of hazardous drugs in the pediatric intensive care unit reaffirmed that aspirin is contraindicated in children up to about 18 with a suspected viral illness because of the Reye’s syndrome risk, while noting that it remains necessary for specific conditions such as Kawasaki disease and after certain heart surgeries (Beckers et al., 2026). What this means for you: the everyday advice to avoid aspirin in young people with viral infections still stands, and the exceptions are narrow, doctor-supervised situations rather than something families judge on their own.
Glossary of key terms
| Term | Definition |
|---|---|
| Encephalopathy | A general term for damage or dysfunction of the brain, which in Reye’s syndrome means acute swelling. |
| Salicylate | A family of medicines that includes aspirin and bismuth subsalicylate, linked to Reye’s syndrome in children. |
| Cerebral edema | Swelling of the brain that raises pressure inside the skull and drives the most serious symptoms. |
| Hyperammonemia | A high level of ammonia in the blood, a hallmark laboratory finding in Reye’s syndrome. |
| Microvesicular steatosis | The pattern of tiny fat droplets inside liver cells seen on a biopsy in this condition. |
| Inborn error of metabolism | An inherited disorder of body chemistry that can cause a Reye-like illness and must be excluded. |
| MCAD deficiency | A fatty-acid oxidation disorder that can mimic Reye’s syndrome and is often found on newborn screening. |
| Antipyretic | A medicine that lowers fever, such as acetaminophen or ibuprofen, used in place of aspirin in children. |
Frequently asked questions
How does aspirin cause Reye’s syndrome?
The precise mechanism is still not fully understood, but aspirin and other salicylates appear to interfere with mitochondria, the tiny energy factories in liver and brain cells, in a way some children cannot tolerate during a viral infection. The result can be the liver injury and brain swelling that define Reye’s syndrome. What is certain is the strong statistical link, which is why aspirin is avoided in children and teens with viral illnesses even though not every exposed child is affected.
At what age should children avoid aspirin during a viral illness?
General guidance is to avoid aspirin and salicylate-containing products in anyone under about 19 years old who has a viral infection such as the flu or chickenpox. Acetaminophen or ibuprofen are the usual alternatives for fever and pain. The main exception is a child who has been prescribed daily aspirin for a specific medical condition, whose care is directed by their own doctor.
Can adults get Reye’s syndrome?
Reye’s syndrome is overwhelmingly a disease of children and teenagers, and true adult cases are extremely rare and sometimes difficult to confirm. Adults who had the illness as children and have questions about taking aspirin should discuss their individual situation with a clinician rather than relying on general rules.
Can Pepto-Bismol cause Reye’s syndrome in children?
Bismuth subsalicylate, the active ingredient in some stomach remedies including Pepto-Bismol, is a salicylate, and salicylates are exactly what should be avoided in children and teens with a viral illness. For that reason these products are generally not recommended for young people who may have a virus. Read labels for salicylate ingredients and ask a pharmacist if you are unsure whether a medicine is safe.
What is the classic triad of Reye’s syndrome?
The condition is classically described by a recent viral infection, sudden brain dysfunction (encephalopathy) with vomiting and confusion, and liver problems marked by fatty change and abnormal blood tests. Doctors recognize it by that sequence together with the distinctive laboratory pattern of high ammonia, elevated liver enzymes, low blood sugar, and slowed clotting, usually without jaundice.
How common is Reye’s syndrome today?
It is now very rare. After public-health warnings in the 1980s advised against giving aspirin to children with viral illnesses, reported cases fell dramatically and have stayed extremely low ever since. The decline is widely regarded as a clear example of a public-health message preventing a serious disease, and it is why avoiding aspirin in young people remains so important.
Sources
- National Institute of Neurological Disorders and Stroke — Reye’s Syndrome — NINDS Health Information, 2024 — ninds.nih.gov
- Mayo Clinic — Reye’s Syndrome: Symptoms and Causes — Mayo Clinic, 2024 — mayoclinic.org
- Cleveland Clinic — Reye’s Syndrome: Preventing and Recognizing It — Cleveland Clinic Health Library, 2023 — my.clevelandclinic.org
- MedlinePlus, National Library of Medicine — Reye Syndrome — MedlinePlus Health Topics, reviewed 2024 — medlineplus.gov
- Gibson C, Noyes J, Goliger M, Guo J — Adult-Onset Reye’s Syndrome and the Risks of Low-Dose Aspirin Rechallenge: A Review of Current Literature and Future Directions — Cureus, 2025 — doi.org/10.7759/cureus.96332
- Glab-Jablonska E, Taybert J, Wisniewska A, et al. — Medium-chain Acyl-CoA Dehydrogenase Deficiency Identified by MS/MS Newborn Screening Challenges — Journal of Mother and Child, 2025 — doi.org/10.34763/jmotherandchild.20252901.d-25-00025
- Beckers L, Verbruggen J, Saldien V, et al. — Potentially Hazardous Drugs in the Paediatric ICU: A Narrative Review on the Exemplary Cases of Propofol, Chloramphenicol, and Acetylsalicylic Acid — Children (Basel), 2026 — doi.org/10.3390/children13040579
Further reading
- Understand the clotting tests mentioned above by reading this guide to your coagulation test results.
- Explore how technology reads abnormal liver results by reading this guide to interpreting liver enzyme spikes with AI.
- Learn how clotting speed is standardized by reading about what the international normalized ratio (INR) means.
- Read about another illness caused by the varicella-zoster virus in this guide to shingles symptoms, causes, and treatments.
- Build a fuller picture of your own numbers with this guide to reading reference ranges, flags, and trends in a lab report.
Understand your lab results with BloodSense
Recognizing Reye’s syndrome rests on a distinctive pattern of blood tests, from a high ammonia level and rising liver enzymes to low blood sugar and slowed clotting, often with a normal bilirubin. Those same markers appear on ordinary lab reports for many reasons, and they can be hard to interpret on your own when a value is flagged high or low. BloodSense translates a full lab report into plain language, showing where each value sits relative to its reference range and explaining what an abnormal liver enzyme, ammonia, glucose, or clotting result means.
Whether you are following up on a child’s illness or your own bloodwork, understanding the numbers is a strong first step toward a useful conversation with your clinician. Get your results interpreted in minutes
