Record High Pollen Levels? Here's Why Sniffling and sneezing your way through spring? Record high pollen levels in some places may be to blame. But why do plants produce more pollen in some years? Aerobiologist Estelle Levetin explains the biology of pollen production and the reasons for the yearly variation.
NPR logo

Record High Pollen Levels? Here's Why

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
Record High Pollen Levels? Here's Why

Record High Pollen Levels? Here's Why

Record High Pollen Levels? Here's Why

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

Sniffling and sneezing your way through spring? Record high pollen levels in some places may be to blame. But why do plants produce more pollen in some years? Aerobiologist Estelle Levetin explains the biology of pollen production and the reasons for the yearly variation.


Up next, some time for pollen appreciation. Now, I know that you're out there hacking, wheezing and sneezing and doing all that stuff. You say, how can I appreciate pollen? I'm suffering from the allergies this spring. Because this has really - been a really bad season for some people in some parts of the country for pollen.

But I'm going to ask you to keep an open mind to try to appreciate pollen from the plant side, from the other side of what - what is pollen's job? What does it do? Why do - this pollen exist, you know?

Without pollen, we wouldn't have many of the plants we've come to rely on. We wouldnt have some fruits or trees or grain crops, or even a perfumy bouquet of flowers. And pollen makes the flowering plant world go round, so to speak. And this year, as I say, there's a lot of pollen going around. Some places of the country are reporting record-high pollen levels. Why is that? Why is this year different from other years? Why do plants seem to make more pollen in some years than others? Wonder about that? Well, we wondered about that, too.

And we're bringing in Estelle Levetin to tell us. She is professor of biology and chair of the Biology Department at the University of Tulsa in Oklahoma. She also runs the aerobiology lab there. Did you hear of aerobiology? She's going to tell us about it.

Welcome to SCIENCE FRIDAY, Dr. Levetin. Hi.

Dr. ESTELLE LEVETIN (Professor of Biology, University of Tulsa, Oklahoma): Hi.

FLATOW: Hi there. What is aerobiology?

Dr. LEVETIN: Well, aerobiology is the study of airborne particles of biological origin. And in a simple sense, it's the study of the airborne pollen and mold spores.

FLATOW: So you don't do chemicals and things like that, just stuff - the biological stuff floating around in the air.

Dr. LEVETIN: Correct. Correct.

FLATOW: And do plants produce more pollen in some years, or are we just - there's a concentrate somehow.

Dr. LEVETIN: Actually, a little of both. It does produce more pollen. Plants do produce more pollen in some years because of the influence of the winter and early spring conditions. Years that had a very cold winter and cold, early spring may actually delay the pollen release. Flowering is delayed. Pollen release is delayed. On the other hand, winters that tend to be mild tend to have earlier pollen seasons.


Dr. LEVETIN: And plants need a certain warm up in the spring in order to flower or release pollen.

FLATOW: Mm-hmm. So if you had, let's say, a very heavy winter, a lot of snow...

Dr. LEVETIN: Mm-hmm.

FLATOW: ...and it stayed around for awhile, that's the formula for a really bad pollen season.

Dr. LEVETIN: Well, in a lot of sense, it is, because it compressed the season.


Dr. LEVETIN: Things get delayed. But once it warmed up, like this year, it seemed to warm up really quickly. We almost went from winter to summer.

FLATOW: Right.

Dr. LEVETIN: And when it warmed up, everything started pollinating.

FLATOW: Right.

Dr. LEVETIN: We, in Oklahoma, normally have pollen release starting in early February, but it was still too cold and too snowy at that time, and so we lost our early season.

FLATOW: Mm-hmm.

Dr. LEVETIN: It got delayed until March.


Dr. LEVETIN: And so that once things started pollinating, it seemed heavier than normal.

FLATOW: Huh. And, of course, I imagine if you have a lot of snow like we really had this winter, you're nourishing all those plants, right?

Dr. LEVETIN: You've got it.

FLATOW: ...with all that water.

Dr. LEVETIN: Absolutely. Although it's treacherous when we're out there in the snow as it's melting, the plants love it.

FLATOW: Huh. So it's like a perfect storm in some places this year.

Dr. LEVETIN: That's right.

FLATOW: Yeah. And what kind of pollen - is there a progression of the kinds of pollen that come out?

Dr. LEVETIN: Actually, there is. I can't speak for every place, but in Oklahoma and I expect in other areas of the South, we see cedar pollen and elm pollen very early. And then we start getting maple, oak, ash, mulberry, sycamore, and it keeps going. We'll pick up walnuts, hickory as we go from April into early May. And then once the trees end, we hit the grass pollen season. And in Oklahoma, that's May. Further north, it's going to be June. And to a lesser extent, the grasses continue all summer.

FLATOW: And is all pollen cause - do they all cause allergies at - the same way?

Dr. LEVETIN: Not all. Some are worse than others.


Dr. LEVETIN: The most notorious, of course, is ragweed pollen that hits us in late summer and fall. As far as the trees go, some of the bad ones are the cedar, the elm, oak, mulberry pollen is pretty allergenic, ash. So there are a lot of highly allergenic trees.

FLATOW: So when people say they look at the flowers, it's not really the flowers they're most affected by. It's the trees.

Dr. LEVETIN: Well, it isn't. Plants with showy flowers are producing pollen that are carried by insects. These don't get airborne. The grains are large and sticky and heavy. It's the plants that produce inconspicuous flowers. So we don't even realize that there are flowers there, they're so small. These are the ones that get wind-pollinated.

FLATOW: Well, as long as I've got you and you're an aerobiologist, then you can talk about molds. Is it a bad year for mold, too?

Dr. LEVETIN: Not yet.

FLATOW: Not yet.

(Soundbite of laughter)

Dr. LEVETIN: But who knows what's going to happen? This is about the time that molds just start off, in April. Of course, there are some year-round, but the levels tend to be low until we get the rains of April and the warmer temperatures of May.

FLATOW: Mm-hmm.

Dr. LEVETIN: So I may not know the answer to that for another few weeks.

FLATOW: I see. You mentioned about the winter affecting this year's pollen. How about the summer or the spring from last year, did that affect?

Dr. LEVETIN: Oh, that certainly can for the trees, because trees actually put on flower buds, and they're in tiny embryonic form. But they're there all winter. They're there - they're formed the previous summer. So growing conditions during the summer of 2009...

FLATOW: Right.

Dr. LEVETIN: ...develop the buds that are now pollinating.

FLATOW: All right. Well, thank you very much. And, I mean, I didn't know there was so much to pollen.

Dr. LEVETIN: Oh, there is. And a lot more.

FLATOW: Now, we're going to actually talk a little bit - a lot more. But I want to thank you very much for taking time to be with us, Dr. Levetin.

Dr. LEVETIN: You're quite welcome.

FLATOW: Estelle Levetin is a professor of biology and chair of the biology department at the University of Tulsa in Oklahoma.


Joining us now is Flora Lichtman. Hi, Flora.


FLATOW: She is our editor, our video editor. And you've got a - well, of course, a related Video Pick of the Week, right?

LICHTMAN: Yes, it is relevant on this, and the pollen appreciation train has been - keep on rolling with it. The - so the pollen news was flying in this week. There is a new study in the journal The Proceedings in the National Academy of Sciences about the architecture of pollen grains. And apparently - so they're these teeny little things, right?

FLATOW: Right. Right.

LICHTMAN: But they have this enormous job to do. I mean, you know, let's just consider what a pollen grain has to do. It carries the genetic material from plant to fertilize another, right?

FLATOW: Mm-hmm.

LICHTMAN: And sometimes these little guys can go as far as miles, apparently.

FLATOW: Mm-hmm. Mm-hmm.

LICHTMAN: But once they leave the flower, they start to dehydrate.

FLATOW: Not a good thing? Good thing?

LICHTMAN: This is not a good thing.

FLATOW: Not a good thing if you're...

LICHTMAN: Apparently, this is not a good thing.

FLATOW: Because when you want to get there, you want to start sprouting your pollen out of it.

LICHTMAN: You want to make sure all of that genetic material hasn't...

FLATOW: Right. Right. Right.

LICHTMAN: ...dried up, basically. So pollen has come up with this really clever adaptation to prevent themselves from becoming sort of completely...

FLATOW: Dehydrated.

LICHTMAN: ...raisin-afied(ph), dehydrated.

FLATOW: Right.

LICHTMAN: Right. And what the researchers, this week reported, which is Eleni Katifori and some of her colleagues at Harvard, was how the geometry of these pollen grains is designed in such a way so that when they start to dehydrate, they fold up.

FLATOW: Like origami.

LICHTMAN: Just like origami.

FLATOW: And they fold - I mean, that's what you're showing on your Video Pick of the Week. If you go to, you'll see Flora's Video Pick of the Week, gorgeous photos, video of how the variety - I didn't know the shapes and varieties of pollen.

LICHTMAN: It's like pollen glamour shots. I mean, they're really...

FLATOW: Pollen runway show, you know?


FLATOW: And they really - and you show video of how the pollen folds and unfolds to self-preserve.

LICHTMAN: This is the neat thing that Eleni Katifori did. She took this, you know, high-power microscope, and over the course of a minute just took picture after picture after picture. So it's a time lapse of pollen...

FLATOW: Right.

LICHTMAN: ...(makes noise) like really coming into themselves like a clamshell. And what they do when they fold up is that they cover the areas where they're losing water, so they just like zip up, kind of -they look like shells or coffee beans, almost, when they're folded.

FLATOW: Mm-hmm. And, of course, when they get there, they have to find a way to unfold.

LICHTMAN: Right. So the - yeah. Of course, this is the miraculous thing. So they - it's just as geometry that sort of folds them up. And then once they reach their destination, they gradually...

FLATOW: Mm-hmm.

LICHTMAN: ...exhale, you know, unfold.

FLATOW: Right. And she studied these? She goes down, collects the pollen...

LICHTMAN: Yes, she...

FLATOW: ...and goes to - out in the field?

LICHTMAN: She actually...

FLATOW: Is she wearing any mask?

(Soundbite of laughter)

LICHTMAN: Yes. I don't know if you can do it if you're a seasonal allergy sufferer. But she said that, actually, she was - we were in Central Park doing the interview, and there are all these beautiful flowers around us. And she was thinking, like, oh, I should really be collecting right now, because you can't get this pollen all the time. You really have to do it at the exact moment when the flowers are producing it.

FLATOW: Mm-hmm. Oh, that's interesting, yeah, because you're taking your work with you, like anybody who's interested in something.


FLATOW: I got to - you know, I know them off the job, but I better take a sample, right now.

LICHTMAN: Right. Right. Exactly. And one of the things that was sort of interesting is that this folding allows pollen grains - it really extends the lifespan. So not every pollen grain does the folding, but it seems like if you are a pollen grain and you can fold, you can survive days...

FLATOW: Mm-hmm. Yeah.

LICHTMAN: opposed to hours.

FLATOW: Yeah. And it was also, from the photos you have there, to see now the little sticky parts, they're like spikes coming out of all that pollen.

LICHTMAN: Yeah. This is a little aside that I was reading - when I was reading about pollen, apparently, the barbs on pollen are designed so that insects can pick them up.


LICHTMAN: And this is, you know - the - my - the person I interviewed is not a biologist, but I think this is sort of a well-known pollen factoid.

FLATOW: Yeah. Well, then you would think that if you want to survive as pollen, that's what you. You'd stick onto something.


FLATOW: And then you get picked up by stuff. Well, that's it. That's -thank you, Flora. That's Flora's Video Pick of the Week. It's on our Web site at, right there in the box on the left. And you can see a lot of other Video Picks of the Week, so - while you're there surfing around. So, thank you, Flora.

LICHTMAN: Thanks, Ira.

FLATOW: We'll see you next week. That's about all the time we have for today.

Copyright © 2010 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.