So You Think You Have Allergies

There's a lot of talk about allergies. But just what is an allergy and what causes them? Why do some people have them while others don't? And why are people with one allergy more inclined to have many?

The immune system is set up to protect our bodies from harmful, foreign substances. Like viruses and bacteria (dirt and germs). Sometimes the immune system doesn't develop properly or is just oversensitive and doesn't react right.

In these cases, it reacts to things that aren't harmful and don'...