Allergies - Are they anything to sneeze at?

Allergies are abnormal immune system reactions to things that are typically harmless to most people. Often according to the medical field we are misusing that term – some things we are intolerant to not allergic. Which may be so, so today we are loosely using allergies to mean all adverse reactions our bodies have to what is going on in our world – the foods we eat, the air we breath, the things we touch… What might be behind them?