You don't know if it has been genetically engineered or modified, what has been added, how it really works and what it's made from. Because some bodies recognize it as a poison, that's why. If you have the flu your body activates certain reactions to help you combat it. This is your bodies way of getting rid of the infection. This is a good reaction.
Fever is a good reaction too.
Your body is heating up to combat the invading viral or infection. Keep a thermometer in the house at all times. Get in the practice of taking temperatures. If the temperature is under 100 then let it be. If it starts moving over 100 then you need to take a natural form of aspirin like the HHA Natural Relief .