In the United States, allergy rates have been on the rise for half a century. According to the American Academy of Allergy, Asthma, and Immunology, or AAAAI--a terrible collection for a Scrabble hand but a pretty good one for a bunch of smart folks in white coats--almost one in 10 adults suffers from hay fever (happy spring!), and roughly the same proportion of children deals with one or more food allergies. When the consequences for an allergic attack range anywhere from a stuffy nose to itchy elbows to anaphylaxis, it's plain to see that this continued upward trend of allergies is a serious problem. And most serious of all? No one really knows why we have allergies in the first place.
Let's start with a little Immunology 101 to understand how allergies happen--more on why they might happen later. Your immune system is made up of two complementary parts: the innate immune response, and the adaptive immune response. Innate immunity responds pretty much the same way to any threat it picks up on: kickstarting some inflammation, thanks to a molecule called histamine, and sending out chemical signals to recruit the blood-cell cavalry to the injured area. The adaptive immune system, on the other hand, is more picky. The white blood cells in your body are each specialized to recognize only a very particular type of invader. That means that any given bacteria will be able to float cheekily past most of these defenders; but if it bumps into one of the cells whose molecules are a match for its creepy little bacteria face--that sends the signal for the serious immune system work to get going.
The problem, then, is that some people's particular array of invader-detecting molecules recognize things that aren't actually invaders. A fleck of dog dander, for example; or a crumble of peanut. For some reason, these people's bodies are making molecules that treat a dust mite's desiccated corpse as something equally dangerous as the bacteria and viruses that cause strep throat, measles, or the flu. Or even more dangerous: the signal can be so strong that a person's immune system kicks into hyperdrive, dumping histamines into the bloodstream at a frantic pace. Our bodies require a delicate balance: too little of an inflammatory response from us and bacteria can ignore it and get on with their pathogenic nonsense; too much, and tissues become so swollen that airways close and eyes squeeze shut. (Antihistamines are drugs that block histamines from being able to do their job, and prevent that "more inflammation!! signal from going out.)
As you may have pieced together, it is not in our evolutionary best interest to shut our bodies down completely over a fragment of walnut ending up in our dinner salad. Evolution, unfortunately, works without the benefit of foresight; and so some options it set up for our immune system in the distant past are now working against us. But what is going haywire, exactly? Scientists don't know for sure, but they have a few ideas.
One of the most popular explanations for not just the existence but the increasing prevalence of allergies is something called the 'hygiene hypothesis'. The very basic idea is that our immune systems have gotten so bored by all the Clorox, 409, and Arm & Hammer in use in our modern world that, without their usual hobby of killing bad guys, they've turned against us to entertain themselves instead. The rather more complicated explanation revolves around a molecule called Immunoglobulin-E, or IgE. IgE is one of those invader-recognizing molecules made by your body's white blood cells, and its particular realm of defense is against parasitic infections: worms, mainly, as well as the creepy critters that cause malaria.
If you live in a developed country, you've probably never had, or even known anyone who's had, a parasitic disease caused by worms--but your body is still cranking out IgE anyway. (In fact, individuals who suffer from allergies may have as much as 10 times as much IgE as other people.)
But if IgE isn't really a bored defender turned delinquent, another scientist suggests that it actually plays an important role in our body's ability to purge itself of unwanted chemicals: the running eyes, drippy nose, and even diarrhea and vomiting that can come along with allergies are all (extremely unpleasant, mind) ways of making things inside your body go outside of it. The increase in allergies, then, is related to the change in our way of life and its corresponding increase in the number of chemicals we're routinely exposed to as part of life in an indoors-oriented society.
Unfortunately, neither eating a pile of tapeworm eggs nor living as a hermit in the great outdoors sounds like a terribly appealing way to rid yourself of your allergies. And with a lot of other factors at play (allergies have some genetic basis, and there also seems to be a lot of correlation with the kinds of allergens you were exposed to at a young age, as well as the method with which you were first exposed to them--on the skin versus inside digestive tract). Either way, there's a lot we have left to understand about allergies; and we should all have a strong inflammatory response to the prospect of stagnant or shrinking research budgets at the NIH when there's so much out there to learn.
(Feature image: itVega / Shutterstock)