The reason doctors say not to take aspirin is because aspirin has side effects and can irritate your stomach lining and also trigger ulcers, bleeding and gastrointestinal upset in some people.
Aspirin also thins your blood and can be dangerous for people that are at higher risk of bleeding.
Aspirin is an NSAID also known as non steroidal anti inflammatory drugs that is widely used for relieving mild to moderate inflammation and pain.
The reason why aspirin causes Reye's syndrome is when it enters your body it can worsen damage to mitochondria and when damaged the mitochondria causes levels of ammonia to increase in your blood which is followed by swelling of your brain.
Aspirin is most commonly associated with Reye's Syndrome.
Reye's syndrome, is a rare but also very serious condition that causes swelling in the liver and brain.
Reye's syndrome can occur at any age but usually affects children and teenagers after a viral infection, most commonly the flu or chickenpox.