|MadSci Network: Immunology|
The easiest way to explain why some people are allergic to anything compared to others is that they have a hyperactive (overactive)immune system. These people's immune systems see the foreign substance (such as dust, food, or antibiotics) as something foreign. It is like a lock and key system. The foreign object is a lock and the body's immune system has keys that "fit" exactly with the foreign object. If there is not a key that "fits" then the body has a build up histamine. This alerts the body's immune system. Because it cannot be identified as helpful or ignored, the body's immune system mounts a defense against the foreign substance that varies in degree. Some people's reactions are so severe that they go into anaphylactic shock.
I have listed a few websites where some of these questions are answered. I hope this helps you
Allergies to pets
Try the links in the MadSci Library for more information on Immunology.