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Every seasonal allergy sufferer has been there. From the moment that first spray of pollen floats through the air, the roof of your mouth begins to tingle, your eyes won’t stay open, and violent sneezes interrupt every conversation. Your body has succumbed to an allergic response to pollen.

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According to the American College of Allergy, Asthma, and Immunology, more than 50 million Americans suffer from allergies each year. Allergens, or allergy-causing substances, are not limited to pollen, but can also include bee stings, latex, gold, penicillin, peanuts, perfume, pecans, salmon, beef, gluten, and nickel. And the allergic reactions that these substances trigger can range anywhere from a few sniffles to vomiting, diarrhea, and—in a small minority of people—a whole-body reaction known as anaphylactic shock.

While they’re a nuisance, our body’s allergic responses, which have existed for millions of years, seem to be a great way to protect us from potentially harmful chemicals. When allergens land on our body, immune cells immediately chomp them up, then adorn their surface with fragments of the allergen. These cells then flow to the body’s lymph tissue, where these fragments are relayed to other immune cells which produce special antibodies that can trigger the allergic response. The allergic response involves a torrent of chemicals that set our bodies itching, coughing, and sneezing.

Even though we know how allergies work, another question that remains is why we have them at all. Margie Profet, an evolutionary biologist from University of California, Berkeley, believes that allergies evolved as a “last line of defense against the extensive array of toxic substances that exist in the environment in the form of secondary plant compounds and venoms.” In other words, as annoying as our allergies can be, they protect us from potential toxins. The speed at which our allergies manifest, she says, also supports her hypothesis that the allergic response evolved to defend against some sort of immediate danger, contrary to the slower immune response our bodies have against viruses or bacteria, which are not thought to pose an immediate threat.

So while some of us might spend spring uncomfortable due to allergies, it’s possible that without our bodies’ allergic responses, we might be in a lot more trouble.

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The Quarterly Review of Biology, Vol. 66, No. 1 (Mar., 1991), pp. 23-62
The University of Chicago Press