Why do we have allergies?
Here's a summary if you're in a hurry:<p>"Why do we get allergies? No one has a firm answer, but what is arguably the leading theory suggests that allergies are a misfiring of a defense against parasitic worms. In the industrialized world, where such infections are rare, this system reacts in an exaggerated fashion to harmless targets, making us miserable in the process.<p>Medzhitov thinks that’s wrong. Allergies are not simply a biological blunder. Instead, they’re an essential defense against noxious chemicals–a defence that has served our ancestors for tens of millions of years and continues to do so today."