Does wildfire smoke affect human fertility? Scientists are trying to find out

The number of wildfires burning across the country has increased over the past few years, and now researchers are trying to figure out if those fires — and the smoke they produce — could impact human fertility.

Susan Shain is a freelance journalist based in Washington State and has written about this.

Full conversation

MARK BRODIE: Susan, how robust is the area of study, in terms of the potential impacts of wildfires on fertility?

SUSAN SHAIN: It’s still pretty new, so most of the studies I found came about in the past couple of years. And it seems like it’s an area that’s starting to be researched more, especially when you compare it to the effects of wildfire smoke on pregnancy. It seems like the area of fertility and reproductive health is still pretty new, and a lot of the research, the researchers have said ... “Proceed with caution. We’re not sure exactly what this means yet, but it does underscore the need for more.”

MARK BRODIE: So given that, as you say, there isn’t a whole lot of research, like are there any conclusions that can be drawn based on what we know so far about the impact of wildfire on fertility?

SUSAN SHAIN: I don’t think there are any definitive conclusions that can be drawn so far. You know, the researchers I spoke with just said to, you know, proceed with caution and that they weren’t sure if people who are trying to conceive should be considered, you know, one of the sensitive groups.

So, I’m sure as you’ve seen, when there’s different AQI alerts, sensitive groups — which includes people who are pregnant, elderly, people with lung or heart issues, children, they should have a different set of precautions than the rest of the population. And what researchers are trying to determine right now is whether people who are trying to conceive should be a part of that sensitive group or not.

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MARK BRODIE: Are there any hypotheses floating around about what might happen to either men or women when they inhale too much smoke or are exposed to wildfires and are trying to conceive?

SUSAN SHAIN: Yeah, so the studies that I looked at for this story looked at both sperm and embryo creation. And so some of the studies that looked at exposure to wildfire smoke for men showed that in most men, after episodes of wildfire smoke, sperm quality and quantity declined. And so whether that actually leads to an impact on fertility is still yet to be determined, but there were significant impacts to sperm quality and quantity.

In another study that I looked at for the story was of patients who were undergoing IVF treatment in Portland, and it looked at how their embryo — the process of creating their embryos, was impacted during a smoke event. And so the people whose embryos were being created during the significant smoke event of 10 days in Portland, when the air was like almost off-the-charts bad, they did end up getting, on average, fewer embryos. And so they’re not sure, you know, what impacts that will ultimately have, but they did get fewer embryos. But the researcher cautioned that it was a small sample size and also that there were a few surprising results, like patients who had been exposed to poor air before their eggs were retrieved and so before their embryos were created in a lab did not see significant harm to their embryos’ development. So she found that really surprising.

MARK BRODIE: So would that suggest then that any amount of wildfire smoke in the air could be a problem — not just like if you are a firefighter, for example, and sort of in the thick of it?

SUSAN SHAIN: Yeah, I mean, I think that’s something they’re still looking at. You know, there was another study that was related to wildland firefighters and looked at their sperm and how their sperm quality has changed, and the results of that study will be published later this year.

But, yeah, it seems like exposure to wildfire smoke doesn’t seem like it’s great for anybody. Whether it’s particularly bad for people who are trying to conceive is still a question that’s up in the air. But the researchers I spoke to, you know, urge people to just check the AQI, stay indoors if the air quality is bad, and try to shut windows and try to use an air filter, you know, regardless of what your fertility goals are.

MARK BRODIE: Yeah, I mean, is this something that folks know about generally? Like this doesn’t seem like something that, as you reference earlier, you know, for folks with particular ... sensitivities to poor air quality, you don’t often think of people who are trying to conceive as in that group. I wonder if this is something that, you know, people who are trying to have kids would even think about.

SUSAN SHAIN: I don’t think it’s something I’ve ever thought about, and I’m in that process. I’m actually pregnant right now, which is part of what made me interested in this. And I have an almost a 5-year-old as well, and so it was something that I had never really thought about. And then, you know, as the air has gotten worse over the years, I started wondering, you know, how is this impacting our fertility?

And I think people are very aware of when you’re pregnant, you need to be more cautious. But I don’t think people think about what happens before you get pregnant, and I think that’s especially true when it comes to men. One of the researchers I spoke with, she specializes in men’s fertility, and she said that she hopes that research like hers is going to draw attention to the fact that, you know, sperm is 50% of the equation. And it really matters what men are doing with their health and their exposures in the months and years ... leading up to when they try to conceive as well.

MARK BRODIE: What did the scientists tell you that they are hoping to study next or really sort of figure out in the, you know, maybe the months and years to come?

SUSAN SHAIN: I think one big thing is whether fertility bounces back after a smoke event. So all of the studies that I looked at for this story were retrospective, which meant that they, you know, looked at data after it had already occurred. So they looked at men’s sperm, you know, before these smoke events and then after these smoke events, but they weren’t able to go back and come back to these men and check their sperm again, you know, months, years later and see if it had bounced back. And so I think that’s something that they’re really eager to study is to see if their sperm quantity and quality declined after a severe smoke event, like how long does it take to recover, if it does recover?

MARK BRODIE: Oh, that’s really interesting. So the idea is that maybe the men are affected for a period of time, but not permanently.

SUSAN SHAIN: Yeah ... they’re not sure because they weren’t able to look at that with these studies. So I think that’s something that they’re really interested in in learning. Part of the the research is being done by wildland firefighters. Wildland firefighters are submitting these these semen samples over the over a year, and that that that study is going to get published like later this year or next year.

MARK BRODIE: Well, I guess that kind of goes to the idea of: Is this something that people are thinking about? It seems like maybe at least to some degree, you know, the folks who are finding these fires, it’s something that either they are thinking about or somebody is suggesting to them that they should be thinking about.

SUSAN SHAIN: Yeah. Well, that was the interesting thing is I spoke to one firefighter who was actually a wildland firefighter and then who was also a student researcher at Colorado State University, and he said that fertility wasn’t a topic that really ever came up while he was on the line. But then when he started talking about his work in the off-season, like how he was working as a student researcher assessing the impact of wildfire smoke on semen, his colleagues were like, “Wait, what?”

And they were also really interested in getting involved. Like, he posted about the study in a Facebook group and received more than 150 messages from firefighters who wanted to participate. And he was kind of blown away by that, that there were so many people who were interested in this topic.

And he said, “You know, there’s kind of a stigma among wildland firefighters. It’s a very like macho, male-dominated world,” and he said it was wasn’t kind of it was kind of a stigma to talking about fertility. But once you kind of got over that, they were really interested in hearing about it, and they were concerned with their ability to conceive.

And so this young man, you know, he helped recruit over 100 wildland firefighters to submit semen samples pre-, mid- and post-fire season over the past year. And so that study is going to look at those semen samples and, you know, their quantity and quality, and that study is going to be published like later this year or the next year. So I’m really looking forward to reading that.

MARK BRODIE: All right, that is Susan Shain, a freelance journalist based in Washington state. Susan, thank you so much.

SUSAN SHAIN: Thank you so much for having me.