Aspirin is a staple in many medicine cabinets. But if you have children, this common medication is a potentially dangerous drug. Aspirin has been linked with Reye's syndrome, a rare but serious condition that can affect children and teenagers recovering from a viral infection.

Reye's syndrome is characterized by swelling in the liver and the brain. Early diagnosis and treatment of Reye's syndrome can save a child's life.

Cases of Reye's syndrome peaked in the 1970s and early 1980s. Today, most children and teenagers who are evaluated for Reye's syndrome don't have the disease. Still, prevention remains important. The basic rule: Don't give aspirin to anyone age 18 or younger, unless specifically recommended by the child's doctor.

In Reye's syndrome, a child's blood sugar level typically drops while the level of ammonia and acidity in his or her blood rises. At the same time, the liver may swell and develop fatty deposits. Swelling may also occur in the brain, which can cause seizures, convulsions or loss of consciousness.

The signs and symptoms of Reye's syndrome typically appear about one week after a viral infection, such as the flu or chickenpox, or an upper respiratory infection, such as a cold. For children younger than age 2, the first signs of Reye's syndrome may be diarrhea and rapid breathing. For older children and teenagers, early signs of Reye's syndrome may include:

• Persistent or continuous vomiting
• Unusual sleepiness or lethargy

As the condition progresses, signs and symptoms may become more serious:

• Irritable, aggressive or irrational behavior
• Confusion
• Weakness or paralysis in the arms and legs
• Seizures
• Loss of consciousness

These signs and symptoms require emergency treatment.

The exact cause of Reye's syndrome is unknown. Reye's syndrome seems to be triggered by using aspirin to treat a viral illness or infection — particularly influenza and chickenpox — in children and teenagers. In some cases, Reye's syndrome may be an underlying metabolic condition that's unmasked by a viral illness. Exposure to certain toxins — such as insecticides, herbicides and paint thinner — also may contribute to Reye's syndrome.

Early diagnosis and treatment of Reye's syndrome can save a child's life. If you suspect that your child has Reye's syndrome, it's important to act quickly. Contact your child's doctor if your child becomes unusually sleepy or lethargic or has sudden behavior changes following a common cold or a bout with the flu or chickenpox. Seek emergency medical help if your child has seizures or convulsions or loses consciousness.

There's no specific test for Reye's syndrome. Instead, screening for Reye's syndrome usually begins with blood and urine tests. Sometimes more invasive diagnostic tests are needed to evaluate other possible causes of liver problems and investigate any neurological abnormalities. For example:

• Spinal tap (lumbar puncture). A spinal tap can help the doctor identify or rule out other diseases with similar signs and symptoms, such as infection of the lining that surrounds the brain and spinal cord (meningitis) or inflammation or infection of the brain (encephalitis). During a spinal tap, a needle is inserted through the lower back into a space below the end of the spinal cord. A small sample of cerebrospinal fluid is removed and sent to a lab for analysis.
• Liver biopsy. A liver biopsy can help the doctor identify or rule out other conditions that may be affecting the liver. During a liver biopsy, a needle is inserted through the skin on the upper right side of the abdomen and into the liver. A small sample of liver tissue is removed and sent to a lab for analysis.
• Computerized tomography (CT) or magnetic resonance imaging (MRI). A head CT or MRI scan can help the doctor identify or rule out other causes of behavior changes or decreased alertness. A CT scan uses a sophisticated X-ray machine linked to a computer to produce detailed, two-dimensional images of the brain. An MRI scan uses magnetic fields and radio waves to generate images of the brain.

More than 80 percent of children and teenagers who have Reye's syndrome survive, although varying degrees of permanent brain damage are possible. Without proper diagnosis and treatment, Reye's syndrome can be fatal within a few days.

Reye's syndrome is usually treated in the hospital. Severe cases may be treated in the intensive care unit. The hospital staff will closely monitor your child's blood pressure and other vital signs. Specific treatment may include:

• Intravenous fluids. Your child may be fed through an intravenous (IV) line. Glucose and an electrolyte solution containing sodium, potassium and chloride may be given through the IV, too.
• Insulin. Small amounts of insulin may be used to increase sugar metabolism.
• Corticosteroids. These medications may be used to reduce swelling in the brain.
• Diuretics. These medications may be used to increase fluid loss through urination.

If your child has trouble breathing, he or she may need assistance from a breathing machine (ventilator).

Don't give aspirin to anyone age 18 or younger, especially to treat a viral illness. This includes aspirin and medications that contain aspirin.

Always check the label before you give your child medication, including over-the-counter products and alternative or herbal remedies. Aspirin can show up in some unexpected places, such as Alka-Seltzer and Pepto-Bismol. Keep in mind that sometimes aspirin goes by other names, too, such as:

• Acetylsalicylic acid
• Acetylsalicylate
• Salicylic acid
• Salicylate

If your child has the flu, chickenpox or another viral illness, use other medications — such as acetaminophen (Tylenol, others), ibuprofen (Advil, Motrin, others) or naproxen sodium (Aleve) — to reduce fever or relieve pain.

There's one caveat to the aspirin rule, however. Children and teenagers who have certain chronic diseases, such as Kawasaki disease and juvenile rheumatoid arthritis, may need long-term treatment with drugs that contain aspirin. If your child needs aspirin therapy, make sure his or her vaccines are current — including two doses of the varicella (chickenpox) vaccine and a yearly flu vaccine. Avoiding these two viral illnesses can help prevent Reye's syndrome.