Why should aspirin not be administered to children under 18?

Aspirin should not be administered to children under 18 primarily because it can cause Reye's syndrome. Reye's syndrome is a rare but serious condition that causes swelling in the liver and brain, and it has been linked to the use of aspirin during viral infections such as influenza or chickenpox. This disease can lead to severe complications, including neurological damage or death.

The risk associated with aspirin use in young individuals is especially concerning when they are experiencing viral illnesses because the combination poses a heightened threat to their health. Thus, health organizations widely recommend avoiding the use of aspirin in this age group to prevent the onset of Reye's syndrome and to ensure their safety during recovery from illnesses.

Other options listed do not have the same level of association with aspirin use in children, making them less relevant to the question.