Why do we have allergies?
Here's a summary if you're in a hurry:"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.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."