When I was a kid, I took a peanut butter and jelly sandwich to school almost every day. In fact, most of the kids in my class ate peanut butter and jelly weekly, if not daily for the entire duration of elementary school—it was our parents' go-to lunch for kids.

Anyone who has had kids more recently than the early 1980s knows that this isn’t the case anymore. Many schools are nut-free zones now, and others restrict the consumption of milk products and even eggs because so many children these days are allergic to these foods. Nut allergies in particular can be incredibly dangerous, so most schools and other public agencies just don’t want to take the risk of allowing nuts into their buildings.

An allergy is when your body treats a particular substance as an intruder, which makes your immune system release various chemicals that cause physical symptoms. Seasonal allergies just generally make you sneezy and sleepy (and grumpy, if we’re naming dwarfs). Pollen, grass, mold, and ragweed seem to be the biggest culprits.

But food allergies—the most common of which are to milk, eggs, nuts, wheat, soy, fish (especially shellfish), and sesame—can cause severe damage to the body and even result in death if not addressed quickly. In fact, 40 percent of children and more than half of adults with food allergies have experienced severe allergic reactions including anaphylaxis.

The reason some people have allergies and others don’t is mostly genetic—if one of your parents is allergic to something, it increases your odds of being allergic as well; if both parents are allergic, it increases your odds even more (Koplin et al., 2013). Eczema is another early risk factor: One study found that infants with eczema were........

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