Plant mating season affects more of us every year. We know it better as spring, that magical time of the year when flowers bloom and trees leaf and billions of pollen grains take flight in an attempt to fertilize another flower. Many of these little plant sperms accidentally end up in our noses, though, where they trigger an immune reaction that we call seasonal allergies.

About 25 million Americans get them—more as climate change worsens—and many of those people take some kind of over-the-counter drug to treat their aversion to plant sex. There are a lot of misconceptions about allergies, perhaps in part because we know amazingly little about how they really work. Our knowledge has exploded (much like pollen in May) in the last decade or so, but there’s still plenty we don’t understand.

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