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Chemicals, Fertility, and Our Future: 22 Minutes with Dr. Shanna Swan
August 24, 2026
Q: So, you’ve spent decades studying chemicals and the link to reproductive health. Was there a single moment in your career when you realized, “This is much bigger than I thought?”
I think a turning point was when I was asked to join a committee of the National Academy of Sciences that had been formed to answer the question: Are these chemicals in the environment that affect our hormones — which they termed hormonally active agents in the environment, what we call endocrine-disrupting chemicals — something that might be affecting human health?
The committee was formed to answer that question: Are these chemicals affecting human health? And this committee, which was in D.C., was composed of three categories of people: neutral people who didn’t know at that point; people who strongly believed that these are harmful — yes, the chemicals are affecting human health; and the other, no, which tended to be more industry-influenced.
So there were three groups, and I was in the middle because I had never actually heard of these chemicals. I had studied lots of environmental factors, but not this class of chemicals. So that was interesting for me, and I learned a lot. And yeah, that turned me around, I think, in terms of my thinking.
Q: When we think about human health and plastics and these chemicals — these endocrine-disrupting chemicals — what do you think people get completely wrong about that link?
That’s a good question. Well, I think it depends which people. Some people ignore it completely. Some people are pretty diligent about reducing their exposure, and some people think it’s a problem, but it’s just too big to do anything about.
So I think what we should be paying more attention to is, yes, we can reduce our exposure, and I’m sure we’ll talk about that. But we should also keep in mind that it’s not really our job to do that. This should be taken care of by the government and by the manufacturers. And so I think that’s the main thing that people get wrong, is not to really recognize who is responsible for regulating this. It’s not me and you.
Q: Your research has truly helped uncover how environmental chemicals affect our bodies. Looking at the evidence today, what do you want people to know about the connection between these chemicals and reproductive health?
I think the first thing I want people to know is that the organism that is most sensitive, and whose exposure will matter the most in the future, is the unborn child. The unborn child is totally captive in this environment and is exposed continually throughout gestation to these chemicals at a time, or times, that the organism is just developing and is most sensitive in the organism’s life to these chemicals.
So if I had to stress one thing, it would be protecting the unborn child. Backing that up a little bit is protecting the environment that the unborn child will enter. And what makes that happen? That is the egg and the sperm. And the male plays a role here, of course. In terms of toxics, exposures to the male before conception can influence that development, as well as what the mother-to-be is exposed to while she’s pregnant.
Q: I was digging into your research a little bit more, and I read that sperm counts have declined dramatically over the past several decades. When you first saw that data, did you realize it would fundamentally change the conversation? We’re having a conversation about it today, about environmental health. Or were you concerned that the findings wouldn’t be taken seriously?
I don’t think I ever believed they would not be taken seriously, because the study you’re talking about — the first meta-analysis study of all the papers in the world that we could find on this topic — gave us information about how sperm count had changed over time, and also how it varies geographically. And this is so fundamental to all of reproductive health.
Of course, it’s the male side, and we can come back to the female side, but that’s much harder. But yes, I believed that this was important to do, which is why I did it with my colleagues. We all thought it was important to do and that it would change the conversation. But honestly, I was not prepared for the huge impact of this study.
It was one of the most highly cited papers in the world according to Altmetric, which is a metric that tracks that, and it’s still talked about. And by the way, I think you know that we followed that up with a second meta-analysis to update it, and we found things that were even more alarming, and we might continue that.
So I think it’s a moving target, but it’s not getting better.
Q: It’s getting worse. Why do you feel it’s not getting better?
Because when we do later updates to the meta-analysis, we see the slope — the rate at which sperm concentration and count are declining — increasing. So it went from around 1% per year to over 2% per year in studies after 2000.
And we don’t know what it is right now because now we’ve moved along. We could look at studies after 2020 or 2025, or whatever we decide to do in the next one, but we want to keep tracking this. We don’t want people to feel it’s a done deal. We want them to realize that it’s an ongoing problem. It’s not a past problem.
Q: Many people today, especially women, wonder whether environmental exposures play a role in infertility and reproductive-health challenges. From your standpoint, what does the science tell us, and what are the biggest questions researchers still need to answer?
When it comes to infertility, there are so many unanswered questions. I guess the one really, really critical one is: What kinds of chemicals are we most concerned about?
Reproduction is governed by hormones. And so if we can isolate and identify chemicals that alter the hormones that are critical to successful reproduction, if those are changing, and we show that those chemicals are causing — I’m using that word deliberately — causing us to be less likely to conceive, which is what I believe, that’s really, really important.
But I have to say, we have much more information on the male side than the female side.
Q: Why is that?
You can pretty easily get a sperm sample. Actually, there are companies — Fellow, for example — where men pay a fee, get a kit, collect their semen at home, send it in, and then get their results: their count, concentration, motility, morphology. These are very reliable. There are a couple of very good, reliable companies.
What do you do on the female side? I don’t know what your experience is, but many, many women know how hard it is to learn about their ovaries and their eggs, their egg count and the health of their eggs, how many are left, and so on and so forth. It requires an ultrasound — things that are quite difficult and costly and sometimes painful. It’s not like giving a semen sample.
And so we actually have much less information. I don’t think we’ll have a meta-analysis of ovarian decline because I don’t think the data are there. It’s just too hard to get this information.
So it’s unfortunate. There are some things we can track. We can track, for example, something called premature ovarian failure, which is the cessation of menstruation earlier than expected. We can measure and keep track of menstrual function: How often do women have their periods? How painful are those periods? How irregular are those periods? And so on and so forth.
There are things we can do by testing hormones to see how hormone levels in the body have changed. But the female side is way behind the male side, and it’s just because the testicles are hanging out. They’re very easy to get a sample from. The ovaries are not.
Q: Switching gears for a minute, for decades we’ve treated environmental protection and public health as separate conversations. Do you think science has shown us they’re actually one and the same, and that we need to adjust the way we communicate about the two?
I do. And I think it’s even more — I’d add a couple of layers to that. I would say the picture involves health, reproductive or other, but it also involves the health of not only humans, but other species.
And then, in terms of when you get to the causes, it involves fossil fuels. So I like to talk about the triple threat: climate change, biodiversity loss and reproductive decline. They’re all part of the same picture.
I like to use this image of a three-headed Hydra sitting in a pool of oil. You know what that is, that monster? There’s a monster sitting there, and it’s producing climate change, of course, coming from fossil fuels, biodiversity loss, and then failure of reproductive health.
These are not separate problems. They’re all interlinked. But the problem is, with the Hydra, you can’t cut off one head. You can’t just control, say, biodiversity loss — even if you could — and get rid of the fossil fuel problem and so on. You have to deal with all of them together.
Q: At EARTHDAY.ORG, we have launched a global campaign around food because we truly believe that what we eat connects climate, environmental health and human health. When you think about plastics and food and chemical exposures, do you think people should start asking not only, “What’s in my food?” but also, “What has my food been exposed to before it reaches my plate?”
They’re really not separate questions, right? Because what food has been exposed to along the way — if you want to think of it from farm to fork — the things that matter are the things that stay with the food. If there’s something transient and it’s not going to show up in the final product in some way, then why would you worry about it?
But in fact, everything seems to matter that the food meets along the way. The soil that it’s grown in, what’s in the water that it’s watered with, the pesticides that it’s exposed to, what’s in the transport mechanisms, and then how it’s processed. Processing is a huge source of contamination.
It’s processed typically through plastic. I like to think of the tomato as an example. You pick the tomato and it travels in some kind of train or truck, perhaps to a processing plant. In that plant, it’s broken down and we’re going to make sauce out of the tomato. Then it goes through various steps, including being passed through plastic tubing.
Now, it’s not typically tested for chemicals at that point. But I want to tell you that there are other things that are passed through plastic tubing that are tested. One very dramatic example is children in the neonatal intensive care nursery. This sounds very different, but it actually is similar because those children are being fed and given various things through tubes.
Those tubes are made of soft plastic. Soft plastic is soft because phthalates are added to the material that makes the tube. And those phthalates lower testosterone. They interfere with hormone function. They interfere with reproductive hormone function, and they affect the growth of those children.
How do we know that it plays a role? It’s very simple. You can count the number of tubes that are going into an infant in the NICU, and then you can get their urine, because that’s how you test the level of phthalates in the organism. You run it through a lab that tells you how much phthalate is contained in that urine. And that turns out to be proportional to the number of lines that are going into the newborn.
Here’s another very different example. They did a study in Eastern Europe on a farm — a very clever, simple study. They milked cows the old-fashioned way with a hand milker, and then they milked the same cows on another day with a milking machine. The milking machine contains plastic tubing.
They tested the milk in both cases for phthalates. The hand-milked milk did not contain phthalates, and the machine-milked milk contained phthalates. So whatever you’re passing through this plastic tubing is going to pick up.
The phthalates are put into the plastic matrix to make it soft and flexible. And then when you use it — particularly if you heat it — the phthalates that are put in there to make it soft and flexible are not chemically bound to the matrix. And so they leave it and they go into the food, the milk, the baby. And then we can measure it.
This is why you can’t heat food in plastic. When you heat it, those chemicals can migrate into the food.
Q: Your recent intervention study, featured in the Netflix documentary The Plastic Detox, found that participants who made practical lifestyle changes showed measurable reductions in BPA and phthalate levels — common chemicals found in everyday consumer products — in just a few months. What did that research teach us about our ability to reduce exposure, and how can we educate the public to really understand and test those levels?
Just for people who haven’t seen the movie — and I hope everyone watching this will see the movie — it’s a Netflix movie. What we did was enroll a very small number of couples, and this was only a pilot. By the way, we are applying for federal funding to do this in a much larger sample, and we’ve published it in a scientific journal. So it’s not big science, but it is science.
We enrolled these couples, and there were six originally, and one dropped out. Then we worked with a company called Million Marker. Million Marker did two things. Later, when we got the samples from the subjects, they tested them for these chemicals. But they also spoke to all of these people very personally and often during the three months of the intervention.
They asked them: What did you put on your face this morning? What did you wash your clothes with? How do you store your food in the kitchen? How do you cook your food? And on and on — all the areas where we can get these chemicals. They asked them to try to understand what they were doing and what products they were using that might impact their levels.
Then they talked to them about how to reduce those exposures — actions they could take. You might store your food in glass instead of plastic. You might change out your frying pans so that they’re not nonstick — and by the way, that’s not phthalates, that’s PFAS. You might change your water bottles. Those hard water bottles are actually bisphenols, not phthalates or PFAS, and so on.
So they went into these different areas where people could make changes and suggested these changes. And then this is the hardest part and the most dramatic: I went to their houses. I went to all of their homes.
I brought a big box. This box was actually about $500 worth of products, and I gave it to them as a present. In it were alternative products: different toothbrushes, different soap, different laundry soap, different storage jars, different frying pans, and so on and so forth — things that they could use that would reduce their exposure.
Then we got urine samples at the beginning, at the middle and at the end — at the beginning, six weeks and 12 weeks. It was a 12-week intervention. We asked them what they were doing at those points, and then we looked to see what their levels of these chemicals were in their bodies.
We also had the men give us semen samples, and we looked at the quality of their semen. So the hard measures were their sperm count and so on, and what their body burden was.
And finally, we had quite a few pregnancies, which was really exciting because these couples had been trying for a long time to get pregnant unsuccessfully. It was pretty incredible.
By the way, there were some unexpected benefits that we hadn’t tracked or hadn’t built into the study protocol. We asked them about their sleep and got reports. These are soft endpoints that I wouldn’t put a lot of weight on until we study them in the next study, when they’ll be systematically collected. But many reported sleeping better, many reported being less anxious and many changed their lives.
For example, you’ll see in the movie that one of our men is a preacher. That’s Eric. Eric was so impressed and convinced by this little intervention that he entered law school, and he is now studying law to pursue environmental law. This is his life now.
Q: A lot of our constituents always like to know, “What can I do?” So if you walked into my home today, what are the first three changes you’d recommend to reduce my exposure to plastics and harmful chemicals, and which one would make the biggest impact?
I’ll answer your question, but I’ll say first that there are tools that the film team has produced. One of them is the Unplastic Your Life campaign, where you can go through a house and see where the culprits are — the things you might want to change. In addition, there are some tools that are not related to the film directly.
One of them is EWG, Environmental Working Group. If you’re holding up a new bottle of sunscreen and you say, “Wait, should I have gotten this? Is this okay?” then you go to EWG, go to the consumer guides, look at sunscreens and it ranks the sunscreens. It’s very simple and helpful.
Another simple thing to do is to download an app called Clearya. Clearya does kind of a similar thing but a little differently. You scan the barcode of something you’re thinking of buying in the supermarket, and it gives you a ranking based on what the ingredients are.
Now, I have to say both of these sources do not actually test products. So it’s maybe a little misleading. You might think, “Oh, they’ve tested all these things.” No. What they’ve done is looked at the ingredient list. Then they go to lists out there, like the Proposition 65 list and so on, compare them, look at the number of bad ingredients that are on the list and then rank it that way. That is very useful, but it’s not the same as actually testing.
When you asked me where the science has to go, I mentioned testing products on a global scale. I think that’s a challenge that we as a field are facing, and connected to that is defining what it means for a product to be safe.
If you think about this, it’s not an easy question, because you can ask: Safe for whom? At what stage in life? And so on. I won’t get into the details of that. But the third thing that is probably the hardest of all is to say: What are the safe alternatives? We are all struggling with that, whether it’s biologically based plastic that has a lot of interesting possibilities and some downsides as well.
So I think those are the major problems that we as a society, as a civilization, have to come to grips with. We don’t actually know what it means to say that product A is safer than product B.
Q: A lot of people assume that the kitchen is the biggest source of exposure, possibly because there’s just a lot of plastic. But are we overlooking things like the air we breathe or the clothes we wear by focusing mainly on the kitchen?
Absolutely. The kitchen is, I would say, an easy target, and it’s obvious in some sense — not that it’s unimportant at all — but there’s the bathroom and all the cosmetics.
These chemicals are put into cosmetics because they help absorption. You put some hand cream on your hand, and then you come back and it’s gone, right? Fifteen minutes, gone. So the phthalates make that happen faster. They also hold scent and color. And so anything that’s perfumed is going to have phthalates in it. We showed in our study that women who said they used perfumed products had more phthalates in their urine. It’s measurable.
The air that we breathe contains many chemicals. And now there’s a lot of attention to microplastics, those tiny particles. Those are in the air we breathe all the time and in the water that we drink all the time. So it’s not just one room or one set of shelves that we have to worry about. We have to worry about our total environment.
Q: Thinking about back-to-school season, parents and guardians are thinking about everything from lunch boxes to backpacks, school supplies and snacks. What are some changes families can make to reduce their children’s exposure to harmful chemicals without feeling totally overwhelmed?
I’ll tell you in a minute, but I want to preface this by saying these changes are often not cheap, and so the ability to protect yourself is not an equal-opportunity activity for everybody.
First of all, communities or people that are disadvantaged don’t have the time to learn about this, read about this and find out what the alternatives are. They’re disadvantaged, and they may not have the resources in their neighborhood. There may not be a market nearby that has fresh food, and they may not have the money to buy organic food.
So I’m going to tell you a few things, but recognize that this is a disparity — not everybody has the same ability or possibility of protecting themselves.
One thing we hadn’t mentioned — you mentioned clothes in passing — is that fabrics are really important. Fabrics are my sofa, my rug, my curtains, my clothes. My clothes, particularly if they’re waterproof or stain-proof, are going to contain PFAS.
So one thing you could think about, if you can afford it, is to buy natural fabrics. You want to buy clothes made of linen, wool and cotton. Those are more expensive, absolutely.
Water is a really big concern for me: drinking, showering, bathing. You can do things, but you have to do them carefully because you don’t want your distiller or your filter to introduce more plastic into the water. You have to buy devices or use techniques that don’t make things worse.
And I can’t avoid saying the microwave is a tricky device. It’s helpful and it’s dangerous because we can’t microwave in metal, of course, we know that. But we can’t microwave in plastic either. Many foods are designed to be microwaved in plastic, and that just blows me away. It will introduce the chemicals into the food directly. So don’t do that. Don’t put food in a plastic container and heat it if you want to consume that product.
Q: It’s kind of wild that there’s no regulation. How is there no oversight on this yet, when we know it’s directly affecting our bodies and the bodies of our unborn children?
I want to come back to that because there’s something called the phthalate syndrome.
It’s interesting. I don’t know of any other medical developmental syndrome that is named after a chemical class. So how did that happen?
First of all, human urine was tested and found to contain phthalates. We all have phthalates in our bodies. This is a representative sample of the U.S., so a high percentage of people have phthalates in their bodies.
Around the time they were finding this, the National Toxicology Program started saying, “Okay, it’s in everybody. Let’s see what it does. Start with animals.” What does it do to the offspring of mice or rats that are fed phthalates during pregnancy?
The result was really striking. What they found was — and this was affecting male offspring; other chemicals affect females — the phthalate syndrome affects males. They found that the pups, when they were born, were not completely masculinized.
What does that mean? I hope this isn’t too technical for just a minute. The genital tract in the developing fetus is the same in males and females initially. And then when testosterone comes on board — testes create testosterone — it acts on the genital tract and makes it differentiate between males and females. So you have this divergence into genetic male and genetic female. But it requires that testosterone.
Now, if the organism is being given a chemical that lowers its testosterone, that won’t happen as fully, or maybe at the right time.
The National Toxicology Program saw this. What did they see? First of all, they saw that the testicles were less likely to descend into the scrotum. The penis was smaller. There were other changes — I’ll leave those aside because they’re a little more technical — but the most dramatic was how much space the genitals took up, how much “real estate” the genitals took up.
That’s the distance from the anus to the genitals — the anogenital distance, or AGD. If you work in a lab, you see that this measurement from the anus to the genitals is typically about twice as long in males as in females.
When the mother is exposed to phthalates at the right time, that distance reflects undermasculinization in male offspring: it’s more feminine, it’s shorter. So, in short, AGD is a reflection of what they call the phthalate syndrome.
Then I said, “Well, that’s interesting. What about humans?” Over a period of several years, I conducted two studies. In the first one, we found the phthalate syndrome. We took urine from pregnant women and tested it for phthalates. We couldn’t expose them deliberately — you can’t feed people phthalates when they’re pregnant. They’re exposed through their daily lives.
So we could see what was in their bodies when they were pregnant. Then we said, “Would you bring your child back so we can examine him or her?” And we did that.
We saw that when the phthalate levels were higher in the mothers during pregnancy, in the critical period, the male offspring were affected. The males had anogenital distances that were shorter and more feminine. They were more likely to have undescended testicles, and they were more likely to have smaller genitalia.
So we found the phthalate syndrome in humans, and we did it again in a whole other study. It was a very important study, and it took a long time and a lot of money to do this twice. But we did establish the phthalate syndrome in humans.
Now, we don’t know what other syndromes are present in humans from other chemicals, and that’s part of the work that we need to do.
Q: We’ve talked a lot about what individuals can do, and we touched earlier on governments. Where do you think the greatest opportunity lies for governments and industry to connect the dots and make this planet a healthier place for all of us and for generations to come?
Jillian, I’m going to answer your question, but first I’m going to point out the story of BPA.
BPA, unlike phthalates, makes plastic hard. And it is estrogenic, not anti-androgenic, which phthalates are. So I like to think of it as the evil twin.
When people started getting alarmed about BPA, manufacturers said, “Oh, no problem, we’ll take it out.” And they took it out and replaced it with BPS and BPF, and now some others. Then they could put a tag on their bottle saying “BPA-free.” But what they didn’t tell consumers was that there was this other phenol in there that actually did a very similar thing. That’s called “whack-a-mole” in our community.
It’s a trick in a way. They can go on making their product and people think they’re safe because it says “BPA-free.” It’s misleading.
So I think what we should have in this country is what they have in the EU under REACH. If a manufacturer wants to add BPS or BPF, for example, they should not be allowed to do that until the replacement or newly introduced chemical is shown to be safe.
That’s the assumption: harmful until proven safe. It’s like guilty until proven innocent. And that’s what exists in the EU. In the U.S., we do not have anything like that. The way we find out if something is harmful is to give it to millions of people and then see what the health effects are over the next 10 or 15 years — all that time exposing people to something that hasn’t been tested.
That, to me, is the biggest challenge we face now. We have to test for safety. And I admit that this is difficult, and we have a lot of work to do on that. Test for safety before a new chemical is introduced into the market. And don’t assume, as TSCA does, that a chemical that has been around for a long time has got to be good and is grandfathered in. “It’s okay, it’s been here forever, we’re used to it.” Never mind about that one.
Q: If we sat down ten years from now, what would you hope has changed in the way that governments, industry and everyday people think about not just plastics, but chemicals and human health?
Of course, I would like a REACH equivalent to be worldwide — good luck on that — so that a chemical will be tested before it’s put into commerce.
And I would like people to be aware of the potential for chemical exposure from things that they might not consider. Who would think that a wonderfully smelling perfume could be lowering their testosterone? But it does, and so on and so forth.
There needs to be an awareness that it’s not all safe until somebody points out a harm. It’s potentially harmful if it’s man-made, and particularly if it’s fossil-fuel-based.
