I have a freakishly large Golden Retriever named Ozzy. He performs some important household chores like waking me up at 6am every day, pre-rinsing the dishes in the dishwasher and destroying any rogue tennis balls that might be laying around the house. He’s two, now, which for a Golden means that he’s still really energetic. If I don’t find time to let him do what he was bred to do, run around like crazy chasing stuff then bringing it back to me, he will start to act out.
The immune system of an allergic person is sort of like Ozzy. It’s designed to to a specific job and do it well and when it isn’t presented with the chance to do that job, it will find something else to do. The part of the immune system that is responsible for allergies is really designed to fight off parasites. We don’t have a big parasite problem is the Western world anymore, but we do have a huge, and growing, allergy problem. One theory as to why allergies are becoming more common states that since the parasite arm of the immune system is not required to do its job much anymore, it goes looking for something else to do. What it finds, instead of parasites, is pollens, dust mites, peanuts, and the rest of the common allergens. It incorrectly senses that these things are potentially harmful and it sets up a reaction to get rid of them. That reaction causes the symptoms experienced by allergy sufferers.
Some people have taken this theory as far as infecting themselves with hookworms to see if it improves their allergies and there are anecdotal reports of this process working. Usually these reports come directly from the people selling the worms, however. There is serious research into this treatment going on at present and the results should interesting. For now, though, we’ll stick to antihistamines, nasal steroid sprays, and immunotherapy.