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t m c » p u l s e | n o v e m b e r 2 0 1 7 34 More than 90 percent of all food allergies are caused by just eight types of foods. Four of those—milk, eggs, soy and wheat allergies—are commonly outgrown, whereas allergies to peanuts, tree nuts, fish and shellfish are often lifelong. Davis said that only about 20 percent of children with a peanut allergy will outgrow it, a statistic made more sobering by the fact that food allergies are on the rise in the U.S. and other developed countries. In fact, research compiled from the Centers for Disease Control and Prevention shows that food allergies in children increased approximately 50 percent between 1997 and 2011. But it remains unclear as to why there has been a surge in food allergy cases, and why food allergies are all but nonexistent in underdevel- oped countries. Theories range from genetic to environmental, and one proposition, the hygiene hypothesis, blames Western culture's obsession with cleanliness. "Our immune system has been geared to fight off things like parasitic diseases, and in first-world developed countries, we're not exposed to these anymore," Davis explained. "We think the immune system has been redirected to attack food." Perhaps that idling of the immune system explains why research related to the microbiome—described by science writer Carl Zimmer as the approxi- mately 100 trillion bacteria and other microbes living inside the human body—is beginning to give clues about food allergies. It is known that the microbiome plays a critical role in the immune system, and research has shown that the composition of the microbiome is related to the susceptibility of food allergies. In fact, studies using mice models have shown a class of bacteria called Clostridia protected mice against certain food sensitizations, which could potentially lead to future development of probiotic therapies. Researchers and clinicians are opti- mistic that treatments for food allergies will be developed, but until then, the only course of action is avoidance of the specific food group. Still, there are the lucky ones who, for reasons not com- pletely understood, experience a drop in their IgE antibodies. Some of them will sit at a doctor's office and take a series of smaller bites, then larger ones. Then, like Parmer, they'll celebrate with something long forbidden. "The first thing I had was a Reese's Peanut Butter Cup," Parmer said. "It was really good."