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Sneezing in the rain.

I'm Bob Karson with the Discovery Files, from the National Science Foundation.

(Sound effect: spring music, birdies) When spring is in the air, so's the pollen. (Sound effect: cartoon sneeze). With allergies, I usually (Sound effect: doors slam, windows shut) hole up indoors, pop some antihistamines and hope (Sound effect: light thunder, rain) for a rainy day (Sound effect: steady rain) I mean, rain kind of cleanses the air, right? A new study from researchers at the University of Iowa says, well, that's partially true. A good rain really does keep full-size pollen grains in check but we're not 'out of the woods' yet.

Right in their own back yard, in Iowa City, the team found tons of tree pollen, and ample rain for their study, over a month and a half in spring 2019 -- prime tree pollen season. There were 28 days of 'rain events' -- from sprinkles to major downpours.

(Sound effect: windy rainstorm) Since pollen grains can break up in high humidity, the team found as they're swept up into the storm's soaky updraft, they fragment. The ultra-light fragments are way smaller sometimes about 1/10th of a grain that go flying and get blown back downward with the rain. The really high concentrations will get ya mostly when it's raining, but concentrations remain elevated two-and-a half to eleven hours after a rain. The bigger the storm, the more they're around.

If you have seasonal allergies, it might be a good idea to chill at home a few hours during and after a heavy rain.

Stallin' 'cause the pollen's still a-fallin.'

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