It’s difficult to ignore the recent prevalence of allergies in the United States today. Gone are the days of swapping lunches in the school cafeteria and munching on salty airline peanuts. Today’s world is full of allergy alert bracelets and nut-free, wheat-free, dairy-free, egg-free cookies. These changes are necessary, since up to 15 million Americans have food allergies today. In fact, food allergies affect 1 in 13 children under 18 years old: that’s an average of two kids in every classroom. And that number keeps rising—a 2013 study by the Centers for Disease Control and Prevention (CDC) showed that the number of American children with food allergies jumped about 50% between 1997 and 2011. Although this change may partially result from more children seeing allergists and receiving a diagnosis than in the past, that’s still a staggering leap. Of course, food isn’t the only culprit causing allergies—almost 8 million children in the United States experience respiratory allergies, and almost 9 million children suffer from skin allergies. Many children outgrow their allergies, but some struggle with them for the rest of their lives. So what’s going on? That’s the same question researchers are asking. Unfortunately, we’re not quite sure what’s causing this allergy epidemic. But we do have some promising theories, and researchers are closer than ever to cracking the code. The Hygiene Hypothesis Although this surge in allergies seems like a new phenomenon, the leading theory behind it was actually first proposed in 1958—but it’s more relevant than ever today. In a nutshell, the hygiene hypothesis theorizes that we’ve become too clean for our own good. The thought is, although our Western anti-bacterial lifestyles help us to avoid infections (great!), the bacteria we’re killing or avoiding are instrumental in training our immune systems to differentiate between harmless and harmful irritants (not so great). Without these helpful bacteria, our bodies become hyper sensitive to foreign particles, and react accordingly—causing allergic reactions that sometimes include life-threatening anaphylaxis. The hygiene hypothesis leaves us with a lose-lose outcome: in effect, it’s like saying, “bacteria: can’t live with them, can’t live without them.” By using anti-bacterial soaps, decontaminating our water supply, pasteurizing and sterilizing milk and other food products, vaccinating against childhood infections, and using antibiotics, we’re protecting ourselves against life-threatening infections like hepatitis A and childhood diarrhea. These infectious diseases still chronically affect countries where high health standards don’t exist. But on the other hand, the number of people with allergies in those countries is very low. And researchers have found that when those countries put measures in place to eliminate common infections, the rate of allergic diseases rapidly increases. But there is hope: studies have shown that children who grow up on farms develop fewer allergies, possibly because being around farm animals exposes these kids to more germs, which help their immune systems learn what to attack and what to accept. So, while your instinct may go against letting your toddler crawl around in a barn, it turns out it might be the best thing for him. And a recent 2015 study revolutionized the way we think about food allergies—researchers found that introducing peanut-based products to infants actually prevented them from developing an allergy to peanuts. This finding goes against the prevailing theory that early introduction of allergens actually increases the risk of developing an allergy. Essentially, exposing young kids to allergens has been shown to help strengthen children’s immune systems—not weaken them. A Gut Feeling In the same vein of the hygiene hypothesis comes the theory that the decrease in specific bacteria found in our gastrointestinal tracts is related to the increase of allergic conditions in our society. Because of a variety of factors, like our super-hygienic environments, the rise in cesarean section (C-section) births, and the increase in antibiotic use, children are less exposed to gut microorganisms, which are thought to help the immune system develop. In a natural birth, an infant’s digestive tract picks up microorganisms from the mother; these microorganisms set off a complex order of events that drive the healthy regulation of the baby’s immune system. However, children born by C-section skip this part, which may lead them to develop allergies. In addition, the prevalence of antibiotics correlates with the prevalence of allergies—antibiotics kill bad bacteria in our gut, of course, but they also kill the beneficial bacteria that serve to strengthen our immune systems. When these helpful bacteria are lacking, our immune systems are lacking, as well, and we become more susceptible to allergic disorders. That’s why it’s so important to only take antibiotics when you absolutely need them. Again, though, there’s hope: you may have heard about the public’s latest obsession with fermented foods and yogurt. That’s because both contain probiotics, which are essentially the “good” bacteria we may lack in our guts. By eating these foods, or taking probiotic supplements, we reintroduce these helpful bacteria back into our systems, where they are theoretically able to help our immune systems get back to normal. Blame Your Genes Another theory behind the rise in allergies relates to genetics: your risk of developing allergies doubles if you have one parent with allergies. Scientists have identified specific changes in specific genes in people with allergies—genes that they pass along to their children, who pass them along to their children, and so forth. In effect, allergies beget more allergies. Researchers are still determining how this knowledge can help them treat and prevent allergies, but it’s a big step in the right direction. Looking to the Future Scientists are studying the cause of the rise in allergies—and they’re also looking at ways to treat them in new and innovative ways. Novel therapies that train the immune system to accommodate allergens, like oral immunotherapy and sublingual (under the tongue) immunotherapy are helping people tolerate allergens and reduce the likelihood of severe allergic reactions like anaphylaxis. Yes, it’s unfortunate that allergies are so prevalent today—however, this surge has led to a renewed focus in finding the cause and most effective treatments for allergic conditions.