Can planting more trees make allergies worse?

Trees provide shade and clean air in congested cities, so planting more of them seems like a straightforward solution. But trees also produce a natural pollutant— pollen. In this episode, producer Juan Diego Ramirez reports on the link between growing urban canopies and allergy exposure, and what you can do to protect yourself. Interested in more health stories? Email us your question at [email protected] mailto:[email protected]. Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org http://plus.npr.org. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:36Speaker 02

  You're listening to Short Wave from NPR.

• 0:42Speaker 01

  If you live in a city, heck, if you live anywhere, you know how important trees are for a person's well-being. They provide shade and shelter, perches for chirping birds. They clean air, manage stormwater in places like New York, Chicago, Detroit, Miami. They are a refuge in the concrete.

• 0:59Speaker 03

  Yeah, they're great in many ways, but I gotta tell you, Nate, they're not perfect.

• 1:04Speaker 01

  Ooh.

• 1:05Speaker 03

  As someone who suffers from asthma and gets wrecked by pollen.

• 1:09Speaker 01

  OK, Juan Diego Ramirez, you produce the show every week, so I know that nothing could actually wreck you.

• 1:17Speaker 03

  Oh, man, you'd be surprised. For me, I call this the hospital season.

• 1:22Speaker 01

  Oh, my gosh, OK, it's that bad. So how are trees sending you to the hospital?

• 1:27Speaker 03

  OK, well, tree pollen can build on many factors and cause asthma flare-ups, right? Like where breathing gets difficult and there could be a lot of coughing. We've seen chest tightness because of the pollen irritating the airways, right? And I thought I was alone, and I learned that it's not just a me problem. There are tens of millions of people like me in the US who suffer from asthma.

• 1:52Speaker 04

  Pollen interacts with air pollution from the cars and the trucks. And that makes the pollen basically like super pollen. And that makes them much more allergenic.

• 2:06Speaker 03

  Nate, that's Tom Ogrin, a horticulturalist based in Salo Luizo, baseball, California.

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  As the climate changes, the more you increase carbon dioxide in there, the more these male trees produce pollen.

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  Tom has been studying urban tree canopies for decades and attributes why pollen has been more on the rise across the country to a few factors. One of them, which is climate change.

• 2:31Speaker 01

  Right, because climate change creates warmer weather, making trees bloom earlier in the year, making pollen seasons last longer, right?

• 2:39Speaker 03

  Exactly, right? So people whose allergies are triggered by pollen tend to have a bad time during pollen seasons, like me, which happens most of the year.

• 2:50Speaker 03

  Tom calls this a perfect storm.

• 2:53Speaker 04

  Where the bloom season is getting longer, they're producing more and more pollen every year, not less, which is absurd because that's not what we want to do. We want clean air.

• 3:13Speaker 01

  So today on the show, the complicated reality of more tree cover in cities. They're important for local ecosystems and they help keep cities cool. But how trees and urban green spaces can trigger respiratory symptoms in people living with pollen allergies. You're listening to Short Wave, the science podcast from NPR.

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• 4:48Speaker 01

  OK, JD, it sounds like you've been on a, can we call it a real personal and professional journey with this question about trees, pollen, their benefits, potential risks? I mean, how did this all start for you?

• 5:00Speaker 03

  Oh, man, where to begin? Well, OK, so I grew up in California. And in my mid-20s, I moved to the Pacific Northwest. I started developing itchy eyes. And one day on a hike, I just couldn't breathe. It turned out that I was having an asthma attack.

• 5:17Speaker 01

  Oh, man, what a terrifying way to learn that you have asthma.

• 5:21Speaker 03

  Yeah, it was very scary. But this kind of thing happens to a lot of people, right? You move to a new place you're not used to, and your body's sometimes like, hey, what the heck? You are in this new environment. There's new plants, there's all these new things.

• 5:36Speaker 01

  Yeah, that totally makes sense. It's like something you're not used to at all.

• 5:39Speaker 03

  Yeah, you know, like, I'm older now and I've accepted my fate. But, you know, I have a kid, so I've been wondering, is it any better for her since she's grown up just in one place, like here in NYC?

• 5:52Speaker 01

  Oh, that's interesting, yeah, I can understand that. I'm a father, too. So what did you find?

• 5:56Speaker 03

  I found this really interesting study looking at pollen and asthma in cities. This study, published in 2013 in the journal Environmental Health Perspective. And it looked at kids living close to tree canopies and if they're allergic to tree pollen.

• 6:13Speaker 05

  What we wanted to understand was whether living in an area with more trees earlier in life would lead to avoiding asthma. That was the hope.

• 6:22Speaker 03

  I spoke to one of the study authors, Gina Lovasi. She's a professor of epidemiology at Drexel University.

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  Importantly, we don't always get the result that we expect.

• 6:33Speaker 01

  OK, so what did she find?

• 6:36Speaker 03

  So basically, within the study, there was four groups, from kids with least to the most tree cover. Moms were recruited during pregnancy, and their children were studied from birth until they were seven years old.

• 6:49Speaker 05

  The group with the least amount of tree coverage near their birth home had 12% showing allergic sensitization to tree pollen. And those with the highest amount of tree coverage, 26% had allergic sensitization to tree pollen. Having this allergic sensitization to tree pollen was much more likely if you had trees around you very early in life.

• 7:14Speaker 01

  Whoa, so what Gina's saying is that people living under more tree cover are more likely to develop allergies to them?

• 7:20Speaker 03

  That's right.

• 7:21Speaker 01

  Oh, man, that seems so counterintuitive to, like, everything we believe about trees being better for air quality.

• 7:28Speaker 03

  Yeah, trees definitely do create better air quality, right? Like, they help reduce pollution. They store carbon, which warms the atmosphere. So there's a lot of good.

• 7:38Speaker 01

  Yeah, a lot of good, but what you're saying is there's kind of a double-edged sword here.

• 7:42Speaker 03

  Exactly.

• 7:43Speaker 01

  OK, what are some things we can do about this, then, JD? Because, like, we need trees, right?

• 7:50Speaker 03

  We definitely do need trees. So the first thing people can do is just be aware of when pollen season is for the plants that you're allergic to. So for me, my interest is in tracking tree pollen. But other people are also allergic to other vegetations. I talked about this with Dr. Jay Portnoy, an allergist at Children's Mercy Hospital in Kansas City, Missouri. And he says pollen season occurs at predictable times in a year. So if you're allergic, you can keep track throughout the year. One of those seasons, Jay says, runs from around May into early July.

• 8:28Speaker 06

  It's a very intense season, one giant season, six to eight weeks long. And it causes a lot of misery in the late spring, early summer months. Pollen tends to decrease in July and early August. It's really hot at that time of year, and so the plants tend to go dormant.

• 8:46Speaker 03

  So later in the year, there's ragweed season, which starts in mid-August. That peaks around Labor Day and then in late September into early October, ragweed pollen decreases. As for trees, some elm trees also tend to pollinate in the fall. But again, Nate, these are regional, so you have to look at what's blooming in your neck of the woods, right, around each season.

• 9:14Speaker 01

  That makes total sense because this country is so vast and there is so much biodiversity. It's not like, you know, Phoenix, Arizona, an arid place would have the same trees and plants pollinating as, say, in Portland, Maine.

• 9:26Speaker 03

  They're very different and have different seasonal patterns.

• 9:30Speaker 01

  So JD, is there anything people can do with that knowledge? Like, any tips for them that you have that might help lessen their symptoms during those really pollen-heavy months?

• 9:42Speaker 03

  Yes. Keep the outside outside.

• 9:46Speaker 06

  Maybe your windows are open more so you're able to get fresh air. You're going to get more pollen. It's likely to trigger your allergies. If you have nasal and eye allergies, it may trigger your asthma, too.

• 9:58Speaker 03

  So during that time of the year, it's a good idea to do things like keeping your windows closed. That goes for, you know, being in your car as well, driving with your windows up. If you're outside for a long period of time, take a shower when you come home. You don't want to bring in the pollen to your couch. I personally have an air purifier on all the time. And lastly, check on the pollen count, right? Like, this is what I personally do every day to see the pollen levels every time I step outside.

• 10:31Speaker 01

  Wait, you can just, like, look up pollen levels?

• 10:33Speaker 03

  You definitely can.

• 10:34Speaker 01

  Oh, man. I had no idea. Okay. So it sounds like these are things that individuals can do. They sound very similar to what people do for wildfire smoke, honestly. But does that mean, JD, that you're kind of just left having to fend for yourself during these pollen seasons and especially in areas where communities are planting more trees because of the other benefits to them?

• 10:57Speaker 03

  Well, one of the things I realized in talking with everyone about this is that this idea of humans versus trees is maybe too simplistic because there are many different types of trees. So it's important to think about what kinds of trees we're planting. Jay says, if you have a variety of trees planted in an area, that can help lower the burden on any one person with allergies.

• 11:23Speaker 06

  If all of them are elm trees, then the elm pollen will be overwhelming during elm season. If you plant a variety of different trees, maybe there will be less of each of the pollens.

• 11:33Speaker 03

  That mix puts less burden on any one person with allergies, right? But that isn't necessarily in one single resident's control. It's something that's in the hands of policymakers, you know, people who might not be aware of this issue.

• 11:47Speaker 06

  And I think urban planners need to take all of those things into consideration.

• 11:51Speaker 01

  Interesting.

• 11:52Speaker 03

  You know, if we can plant more trees in a more mindful way, then everyone gets to reap the rewards.

• 11:59Speaker 01

  Yeah, we get to hang out under trees and toss a ball back and forth with our kids. That sounds great.

• 12:05Speaker 03

  Now, that's a good idea, man. And, you know, whenever we need a break from work, having that more enticing outdoor space can mean the difference between going out for a walk and clearing your head or staying inside and stewing or doom scrolling. And those are real benefits for your physical and mental health that can totally shift how you interact with the world afterwards.

• 12:31Speaker 01

  Totally. JD, thank you very much for bringing us this reporting.

• 12:36Speaker 03

  Anytime, Nate. And now I have to go take my antihistamine meds so I don't have, you know, to start sneezing everywhere.

• 12:43Speaker 01

  Oh, man. I... Good luck to you, my friend. I don't know what to say. This episode was produced by Alana Gordon. It was edited by our showrunner, Rebecca Ramirez. Tyler Jones checked the facts. An Li Wong was the audio engineer. I'm Nate Rot. Thanks for listening to Short Wave, the science podcast from NPR.

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