< Why our allergies are getting worse —and what to do about it

DAVE DAVIES, HOST:

This is FRESH AIR. I'm Dave Davies. When my guest, author and medical anthropologist Theresa MacPhail, finished researching and writing her new book, she made some lifestyle changes. She stopped taking daily showers and changing her sheets as often, along with eating more natural food and making sure to get enough sleep and exercise. Her book is about allergies, which are a growing challenge for humanity as our environment changes. In the U.S., nut allergies in children, hospital admissions for asthma and prescriptions for EpiPens, which treat extreme allergic reactions, have all tripled in recent years. Estimates are that 30 to 40% of the world's population now have some form of allergy.

Some allergic reactions are a nuisance - the congestion and burning eyes that come with a high pollen count - and some are deadly, like anaphylaxis that can follow a bee sting, something MacPhail has had personal experience with in her own family. There are allergies to airborne irritants, food allergies and skin allergies. MacPhail found the causes of allergies to be complex and often misunderstood. For decades, they were thought to mainly afflict people who were nervous, anxious or temperamental. While there's new science on the causes of allergic reactions, effective treatments are hard to come by and expensive when one shows promise.

Theresa MacPhail is an associate professor of science and technology studies at Stevens Institute of Technology in New Jersey. She researches and writes about global health, biomedicine and disease. She holds a Ph.D. in medical anthropology from the University of California, Berkeley and the University of California, San Francisco. Her new book is "Allergic: Our Irritated Bodies In A Changing World." Theresa MacPhail, welcome to FRESH AIR.

THERESA MACPHAIL: Hi. Thanks for having me.

DAVIES: You know, you take us on quite a journey through the world of allergies and how they are changing. You open the book with a story about your father. Why don't you share that with us?

MACPHAIL: Sure. So let me set the stage a little bit. It was 1996, which is going to be important in a second. And my father was in his car with his girlfriend at the time and had stopped at a stop sign. And it was a summer day, late August. And so he had the window rolled down because he happened to be an inveterate smoker. And a bee, just on its daily pollen-gathering trajectory, accidentally flew into his window. My father got confused. The bee ended up stinging him right in the neck, and that set a whole cascade of biological events in process.

So basically, an allergic reaction - an anaphylactic reaction is a little bit like - you've seen the nuclear reaction examples of the ping pong ball. It's similar in your body. One of a few cells in his neck noticed that the bee venom was in his neck, didn't appreciate that - most of our cells don't - and sent out cell signals called histamine. It's just a little compound that cells send out when they're damaged or stressed, and that sends every other cell around it into a similar pattern.

And so before long, my father's cells were just emitting histamine, and histamine does a lot of things in your body. It is one of the reasons you get mucus in your nasal passages. It can constrict the muscles around your lungs. So my dad started to have trouble breathing. It can swell your tissues. So his neck started to swell up, so he couldn't get air that way either. And it also dilates your blood vessels, which ends up crashing your blood flow to your heart. So often, people can go into cardiac arrest during an anaphylactic event.

And unfortunately for my father, he was sitting in the cab of his car the entire time, sitting upright. And so within 30 minutes, he was dead on arrival at the hospital. His girlfriend did drive him to a drugstore, which was the closest medical assistance in our area. We lived in rural New Hampshire at the time, and hospitals were going to be 30 minutes, an hour away. But at the time, laws were in place that the pharmacist could not give my dad a lifesaving injection of adrenaline or an EpiPen injection. His hands were tied.

And at the time, most ambulances - because this is pre-food allergy spike, so anaphylaxis was - I wouldn't say incredibly rare but rare enough that most EMTs just didn't have an EpiPen on hand. And so the ambulance didn't have an EpiPen either. So they basically just had to try to stabilize him and keep him alive to the hospital, and it didn't work. So my dad died that day within 30 minutes of being stung by the bee.

DAVIES: That was a long time ago. Was it something that drove your interest in allergies?

MACPHAIL: Yes, but in a circuitous way because at the time, I was very young. I was only 24 years old when he passed away. And it was quite a shock because we knew he had maybe a mild allergy to bee stings. He had been stung a few times in the past that we knew of, and he had always reacted. But it was quite a shock. And I think that I always have been nervous if I, too, might have a similar reaction, if such a thing could be inherited. But for years, I kind of just panicked whenever I saw a bee at a picnic or when walking through the park. But other than that, I didn't think much about it.

That was until I started getting allergic reactions myself to things like grasses and tree pollen. And then I started wondering if I had inherited those tendencies, if all allergies are alike. And that really got me started on unearthing not just what happened to my dad but what happens to millions of people around the world when they come into contact with something that their immune system just has decided that it shouldn't be there, it just decides it doesn't like - an otherwise harmless substance.

DAVIES: All right. So we'll get into some of the science here, but what symptoms do you have from allergies yourself?

MACPHAIL: Luckily, I'm pretty mild. So my allergies are seasonal and respiratory allergies. I have them all year round. I'm an interesting case because I cannot be tested for what I actually am allergic to, and that's because I have historically low levels of the antibody IgE, which is the antibody that actually reacts to allergens in your body. So I have a localized reaction. So I will get itchy eyes, and I will get stuffy and runny nose and a sore throat. But there's no way to tell because my skin and my blood both don't react to whatever it is in the air that I react to. I've had to guess, basically, based on pollen counts that are released daily. So if I'm reacting, I'll look at the app, like many of us do, and try to figure it out. It's like I'm trying to - a detective trying to figure out what's going on with me.

DAVIES: Speaking generally, allergic reactions are a product of our immune system, right? I mean, what do we know about why our immune system, which protects us from disease, sometimes reacts to bodies in a way that, you know, gives us these troubling symptoms?

MACPHAIL: It's a really interesting question. I think a lot of people in general are confused about what an allergy really is and what a sensitivity is or an intolerance is. And the basic difference is, is that your body can react to a whole host of things, and the symptoms can be similar. But with an allergy, it's really triggering your immune system itself. So your immune cells - there are, you know, billions in your body - they're reacting to foreign objects that it comes into contact with. So that can be anything from a tree pollen to a dust mite. And their jobs are basically - we've heard that they're like police officers. I prefer to think of them as bouncers or curators. Their job is to kind of scan the crowd and make split-second decisions about whether or not that thing is OK to hang out or can become a part of us, in the case of food, or needs to go, in the case of a virus.

DAVIES: And then what happens when pollen comes in, for example, or ragweed or...

MACPHAIL: The way I like to think of it is an allergic reaction is usually driven by a class of antibodies called IgE. And if you think of - we usually hear about T cells, which - those are the police officers of our body. They're constantly circulating and finding things in our body that shouldn't be there. So if a T cell comes into contact with an oak pollen, say, and it says, you know, I don't like the looks of this, it's got to go, it gives that information to a class of cells called B cells. And think of them as nightclub managers (laughter) in your body, on the street that the T cell is patrolling. And he shows a picture of this oak pollen and says, hey; I really don't like this guy. If you see him, you got to let me know. Like, let's contact some people. We got to get it out.

And so these B cells, who are like these nightclub managers, basically, they go to - they produce cells called IgE or little proteins, Y-shaped proteins, and those are like the bouncers. But if you like to think of this metaphor as in, like, every IgE is unique to the perp - so at the nightclub entrance, you've got a bouncer there ready to spot oak pollen, but you've got 50 bouncers at the door all looking for specific things. And so when they see it or something similar to it, they send out the signal. So they alert all of the other immune cells that something's up. You got to come and take care of this guy. So that's basically going on in your body all the time. So the things can either stay, have a great dance party in the club with all of your cells, or they've got to go.

But you can already see the problems because say there's a guy who's 6'2'' with brown hair. He might look similar to something else, and that antibody is still going to react to it. So that's why you get - a lot of people who are allergic to one tree nut will be allergic to all of them, if that makes sense. It's because of the similarities in their protein.

DAVIES: And once the bouncers take action, then we have a rumble.

MACPHAIL: Right.

DAVIES: And your eyes water, and you sneeze, or your skin breaks out or something worse.

MACPHAIL: (Laughter) Yes. Yeah. It's not a very fun nightclub to be in after that.

DAVIES: We'll talk about this some more in a moment. We're going to take a break here. Let me reintroduce you. We are speaking with Theresa MacPhail. She's a medical anthropologist. Her new book is "Allergic: Our Irritated Bodies In A Changing World." We'll continue our conversation in just a moment. This is FRESH AIR.

(SOUNDBITE OF JOAN JEANRENAUD'S "DERVISH")

DAVIES: This is FRESH AIR. And we're speaking with Theresa MacPhail. She is a medical anthropologist who writes about global health, biomedicine and disease. Her new book is "Allergic: Our Irritated Bodies In A Changing World."

There are interesting theories that help or that may help explain why we see so many more allergies in the United States and around the world. One of them, you say, is the hygiene hypothesis. We're just too darn clean. What's going on here?

MACPHAIL: Right. The hygiene hypothesis - if you've heard about it, you've probably heard that we don't let kids eat enough dirt. They don't play in enough dirt. They're not around enough germs. And that's part of it. So what ended up happening is, in the 1970s, this British researcher did a metadata study. So he kind of looked at all the factors involved in developing an allergy. And what he found was that in families that had multiple children, you tended to have - the youngest children had much lower rates of allergic disease. And so he posited that that was probably because they had older siblings who got sick a lot. And so they would bring home all of these bacteria and viruses, and the littlest ones would be exposed to a whole bevy of things that maybe the eldest didn't have the same exposures to. And so that - there was something about this, there was something about being the youngest that was protective.

And, in fact, we have seen that people who send their children to day care centers - there's something about being in a day care center that is also protective and is probably the same theory, that you're just getting exposed to more germs on a day-to-day basis and that, at a young age, that's actually helpful because it helps to train your immune system and - so it's not going to be oversensitive when the kid gets a little bit older.

DAVIES: Yeah. This is interesting. So our immune system kind of needs to learn the neighborhood. It needs to - I mean, it - to distinguish, get to know the various antigens and either how to handle them or how not to worry about them. I don't know. What happens here exactly?

MACPHAIL: Yeah. That's exactly the theory. It's basically - to go back to the bouncer and the police officer, you're absolutely right. It's getting familiar with everything in your neighborhood. So it's your body learning, oh, Bob just lives down the street. He's fine. I don't have to worry about Bob. And if you get that training prior to the age of 3, there's something that happens in early childhood development. By around 3, your immune system is kind of set up, and it's very hard to change it after that point. But it's very malleable before that point, which is why early exposures to things seems to be so protective.

So the landmark studies that support the hygiene hypothesis were done, actually, in Switzerland and Germany, where they found that children who were regularly exposed to dust in animal barns - and it's interesting because the animals seem to be a key component. So if you're living on a farm with livestock, you tend - and you're a baby, and you're being carried by your mom in and out of this barn where there are pigs and cows and ducks and dogs and whatever, you tend to have very low rates of sensitization and allergic response in those adults once they grow up. So there's something happening.

And so the theory is it could be anything. It could be the allergens in the air mixed with certain types of bacteria that would be in a barn. But the animals do seem key. And I will say that if you grow up with a dog in particular, dogs seem to be protective. So people who grow up in a household with a dog also tend to have a slightly lower rate of allergies than people who grow up in a household without pets.

DAVIES: Right. But you want that dog when the kids are little, right?

MACPHAIL: Right.

DAVIES: Right. And just to come back to this - so the older kids who are actually bringing some of these bugs and viruses home - I mean, they're not getting that exposure when they were younger and it might have been more beneficial to their immune system.

MACPHAIL: Right. So when we talk about the immune system, I often heard the experts that I talked to talk about, it's needing to be trained to tolerate certain things. And one of the most interesting things is we don't really understand tolerance. For instance, all the foods we eat are foreign, so we should respond to them in some way because they are foreign particles entering our system except that, of course, we don't. We accept them. We break them down. They become part of us. And so the real question is, how does a cell make that decision? And it seems to be trained very early on in the development of the immune system once the child is born to age three, that it is learning slowly how to do that, how to differentiate. So our cells, by being exposed to a multiplicity of things, somehow learn to be more tolerant.

DAVIES: Right. And it's interesting - you note that that, you know, peanut allergy can be a serious problem for kids and that for a long time, parents were advised to keep their kids away from peanuts when they were little. Turns out to have been exactly the wrong advice, right?

MACPHAIL: Correct. And it's unfortunate. So prior to 2016, when the advice changed, we were, as just normal best practices, telling parents to not only avoid certain allergenic foods like peanuts, strawberries, eggs, milk when they were pregnant, but also to avoid giving them to their younger children until after the age of three. And it turns out that was exactly the wrong advice. And the way we figured that out is a researcher from Israel actually noticed that in places that supplemented their young children's diet with Bamba or this, like, peanut paste, they actually had incredibly lower rates of allergy to peanuts. And so he did a more official study and did find that the early exposure seemed to be protective.

But the tricky thing is, is it's not protective for everyone. So if you give a six-month-old baby a trace amount of peanut butter, say, some of them will learn to tolerate it and some of them will still react because they might already have been sensitized through their skin. And so it's a dice throw. And the best practice now is we tell them, you know, expose to a tiny amount and see what happens. But we could also be seeing an earlier reaction because they've been pre-sensitized. So that's the best advice we can give for now. But it's not perfect advice.

DAVIES: You know, before we wrap up this discussion of this hygiene hypothesis, that increased allergies is in part a function of us getting less exposure to germs and other pathogens when we're little, there's other evidence that kind of leans the other way, that countries with, you know, larger families and that are more based in rural areas are also finding allergies steadily increasing. So it's not all so clear; is it?

MACPHAIL: No, not at all. And in fact - so I grew up in rural Indiana when I was younger. And if this were true, you would think that people growing up in my town, which was a farming community, would have a much lower rate of allergies. And in fact, we don't either. And a researcher at the University of Nebraska found that farmers are sensitized to whole bunches of things - particularly mold, because as grain is stored, it produces mold. So they have a pretty high rate of asthma as well.

And so that is kind of flying in the face of this whole theory that if somehow, magically, if you're exposed or if you live the way that we used to live, that somehow you're protected. But that doesn't seem to be the case. And the other big evidence is places like Uganda, for instance, which is still fairly rural although, you know, a lot of people live in Kinshasa, the city center - but what researchers there have found is that even in the smallest farming villages, if you go out and you look at sensitization rates, they're quite high and that people are starting to develop more respiratory allergies, especially.

DAVIES: So it's complicated.

MACPHAIL: It's complicated.

DAVIES: All right. Let me reintroduce you. We're going to take another break here. We are speaking with Theresa MacPhail. She's a medical anthropologist who writes about global health, biomedicine and disease. Her new book is "Allergic: Our Irritated Bodies In A Changing World." We'll continue our conversation after this short break. I'm Dave Davies, and this is FRESH AIR.

(SOUNDBITE OF HELEN SUNG'S "SUNGBIRD")

DAVIES: This is FRESH AIR. I'm Dave Davies. We're speaking with writer and medical anthropologist Theresa MacPhail. She has a new book about allergies, which studies show are afflicting a growing number of people in the United States and worldwide. She finds there's new research on causes and treatments of allergies, but many still find effective therapies for serious allergic conditions hard to come by or enormously expensive. Her book is "Allergic: Our Irritated Bodies In A Changing World."

There are theories about how our diet and changes to the microbes in our gut, the so-called microbiome, are affecting the course of allergies. What's the theory here?

MACPHAIL: Well, I went to the University of Chicago to talk to one of the top microbiome researchers, and she specifically looks at the development of allergies in relationship to the composition of our gut microbiome. So most people have probably heard by now that billions, trillions of bacteria live inside of our intestinal tract. Our guts are just replete with things that are not us, but that help break down foods and are the reason that we can eat food and turn them into things and stay alive, basically. One theory about the rise of allergies is that over the last 200 years, our diets have gotten dramatically different in terms of what we eat, the types of food we eat - so more processed foods, less fresh fruit and vegetables, different foods, so different diet. And we just eat at a different - in a different way. We cook differently. We manufacture differently. We grow differently. And so that we're feeding ourselves different food, which is a problem for the microbiota that have co-evolved with us.

So for millennia, for thousands of years, they got the same diet or a similar diet, and now suddenly they're being flooded with a lot more fats, a lot more sugars, a lot less fiber. I don't know about you, but I really don't get enough fiber. And that's the majority of us. And so fiber is necessary for a lot of those good, healthy bacteria that are helping us to digest food. And so the theory goes, without all of that, there has been a difference in the composition of what types of bacteria are thriving, what ones are accidentally being starved because they're not getting the right types of food from us anymore. And so if you change that balance in our gut microbiome, then you're throwing off the immune system itself.

DAVIES: And there's also the matter of antibiotics. I mean, we - you know, we get antibiotics when we have ear infections as babies. And we're eating, you know, I guess, food from livestock that have been given antibiotics. Is that a part of this?

MACPHAIL: Yes, absolutely. Researchers - we're constantly harping on about especially the antibiotics being given to the livestock. But even studies have been done to show that if children have repeated doses of antibiotics prior to the age of 2, it dramatically alters the makeup of their gut microbiome because when you take an antibiotic, it's not choosing which bacteria to affect. It's affecting all of them. So, sure, it's taking out the bacteria in your ears that are causing the ear infection, but it's also killing a lot of healthy, good, positive bacteria in the guts. And so we found that if children get too many doses of antibiotics too young, they do tend to be more prone to develop eczema, asthma and food allergies as they age.

DAVIES: Yeah. You know, I think of these problems with, you know, our microbiome as affecting, you know, digestion, but it affects the entire immune system, therefore things like eczema and all of the other things as well.

MACPHAIL: Yes, absolutely, because our guts are lined with mast cells, and they're basically just a thin layer of cells that are part of our immune system, that are part of that process. So they can send up those histamine flags also. They can start a reaction also. So in a child that has food allergies - they might not actually have gastrointestinal symptoms. They might get hives, or they might develop an itch, or they might get wheezing, they might have a wheeze instead of an upset stomach, or they could get stomach pain and/or, in worst case scenarios, as we know, they'll be similar to what my father went through. They'll go into an anaphylactic attack and have a much more serious response from eating a food.

DAVIES: So what's your advice for what we should be eating and not eating?

MACPHAIL: This is so difficult. One of the biggest problems that I faced when I was writing the book is I really wanted to give people hard and fast tips to avoid allergies. But, you know, even the top researchers - there are so many hundreds of different bacteria in our guts. And right now we're only starting to tease out which ones might be crucial to us maintaining a balanced equilibrium of our microbiome that leads to a healthy immune system. So things like taking probiotics don't really work because they're only a few strains of bacteria, and we're not sure that those are the key strains that help maintain that equilibrium.

The best advice that I was given over and over again is just to eat more whole foods and more fruit and vegetables. So getting more fiber is key. So I personally - I'm not a huge vegetable fan, but I have made a concerted effort to make sure that I'm having something green. I've upped my intake of fruits. I eat whole grains now. I grab brown rice rather than white rice. I'm doing my best to try to give a wide variety of foods to a wide variety of bacteria.

DAVIES: You know, this idea of keeping a diverse microbiome kind of dovetails with the idea we spoke about earlier of getting introduced to a lot of germs when we're little - you know, the idea that you don't want to be overly clean. You know, the kid should eat a little dirt maybe and bring that kind of diversity. Is it thought that bathing too frequently or using a lot of detergents is a bad idea? Is that why you've decided you're not going to bathe every day now? You're not going to shower every day?

MACPHAIL: (Laughter) I'd just like everyone to know that I'm perfectly clean.

(LAUGHTER)

MACPHAIL: It's not a problem. I usually try to wait every other day. I mean, there will be times, obviously. We're coming into the summer months. It's kind of - it's hard. It gets harder to make that a reality. But, yeah, the gut microbiome is only one part of this story. The other is your skin microbiome. So there are lots of organisms living happily and healthily and helping our skin out also. And if you'd like to think of your skin as part of the immune system, you should, because it's basically the first line of defense. It's what keeps things out, mostly. And what we've found is if you use harsh detergents, if you put a lot of things on your skin, you are either stripping the skin of some of those natural - again, you're killing off the good bacteria or you're disrupting the delicate balance between fungi and bacteria on your skin, causing a huge problem, or you are just adding more things that your - the immune cells in your skin have to deal with.

So probably most people don't realize that there are 85,000 chemicals on the Environmental Protection Agency's Toxic Control Substances Act watch list. Boy, that was a mouthful. But that's a lot of different, you know, chemicals that we've introduced into our environment, that we're inhaling or that we're coming into contact with through our skin or eating. I mean, you know, there have been lots of research on - I think I read something the other day that we eat about a credit card's worth of plastic every week. So we're just coming into contact with all of these things, and our skin is a barrier.

And so one of the theories of allergy causation is barrier hypothesis. So if you have, quote-unquote, "leaky skin," so if your skin is more porous or is irritated, things are more easily going to get introduced into your immune system and possibly your immune system is going to decide that thing is not great.

DAVIES: So leave your skin alone. Let it breathe a little, right? But my dermatologist says sunscreen all the time, everywhere, and plenty of it. Is this contradictory advice?

MACPHAIL: Well, it's a Scylla and Charybdis situation, I think. You know, skin damage from sun rays is serious and can lead to increase in cancers. Are all of those chemicals confusing our immune systems? Probably. But it's really hard to tell people what's the right thing to do.

I think erring on the side of caution and getting - there are some sunscreens that are made for sensitive skin types. Those are probably better than ones with a lot of perfumes in them or a lot of excess dyes or other things. So just being more careful about what you put on your skin or what you expose yourself to.

DAVIES: All right. So good old long sleeves and hats, maybe, instead of the sunscreen.

MACPHAIL: Right. Right.

DAVIES: You know, one of the things that you said you're also doing less of is you're changing your bedsheets less frequently. Why is that?

MACPHAIL: Well, it's - again, it's a delicate balance. We don't want to let dust mites get out of control. But our skin - the natural bacteria that's just in our environment that we track in throughout the day - it's not a bad idea. It's, again, just exposing my body to a panoply of things. So I tend to change my sheets every other week instead of every week, just to let my body get a little bit more exposure than not, and while still keeping things like dust mites in check.

DAVIES: Let me take another break here. Let me reintroduce you. We are speaking with Theresa MacPhail. She's a medical anthropologist who writes about global health, biomedicine and disease. Her new book is "Allergic: Our Irritated Bodies In A Changing World." She'll be back to talk more after this break. This is FRESH AIR.

(SOUNDBITE OF ROBBEN FORD AND BILL EVANS' "CATCH A RIDE")

DAVIES: This is FRESH AIR, and we're speaking with Theresa MacPhail. She is a medical anthropologist who writes about global health, biomedicine and disease. She has a new book. It is "Allergic: Our Irritated Bodies In A Changing World."

One of the things you say in here is that our pets are, in a way, canaries in the coal mine - those which alert us to a coming danger. What do you mean?

MACPHAIL: Well, I think the fact that we are doing something that is also affecting our pets is the best evidence we have that we're really causing allergies, full stop. And what I mean is there's no evidence that we have, that we know of, that any animal in the wild develops allergic responses. So all mammals, all animals, have immune systems, but only the ones that live with us are negatively reacting the way that we are - so dogs, cats, birds, horses, some pigs, some cows, although less so because they live in barns, not with us. But anything that is really a companion animal has been showing signs of the same sensitization that we are. So in dogs, that'll be a lot of scratching, a lot of itch. In cats, it can be scratching, but it can also be wheezing. A lot of cats get asthma, just like we can get asthma. For birds, it's the same. It's asthma and itch. And for horses, it's asthma and itch also.

So we've been seeing - I actually went to Cornell, to their veterinary school, which is one of the best veterinary schools in here in the U.S. And they said it's absolutely the fact that there's more allergies in pets, except that it's less diagnosed and less surveyed, so we don't have solid numbers, but they've been seeing an increase in rates and it's becoming a larger problem. And their hypothesis is that it is directly linked to lifestyle since our pets are living exactly like we're living, and we have also changed their food. So a lot of this is that we're producing their food exactly the way we produce our food.

DAVIES: You know, I know pet owners who are worried about this. I have a friend whose cat is just scratching itself. And this has been going on for months. And their owners have been trying to figure it out. Do we need pet allergists? Or - I don't know. What do we do? I mean...

MACPHAIL: I think more and more veterinarians are getting on board and learning about and being trained to spot allergies because it is becoming such a big problem. And often, the fix is a specialized diet. I mean, unfortunately, they can be allergic to their food or something in their environment, just the ways that we can. And interestingly enough, a little fun fact is that they can actually be allergic to our dander. So all dander is, is dead skin cells. And so they can actually become sensitized to our dead skin cells just like we are sensitized to them.

DAVIES: And they're complaining to each other about us. I want to talk a little about treatments. You know, you say the most common treatment for typical respiratory allergens is simply avoidance, right? You know, keep an eye on the pollen count. Try and avoid it. Beyond that, you say, you know, thorough household cleaning is something that is done, you know, washing all of the bedding, you know, showering as soon as you come home on a day when the pollen count is high. That would seem to contradict the earlier advice about, you know, tolerating, you know, the microbes around us.

MACPHAIL: Right. But if you wash right when you come in during the pollen season, you're getting the pollen off of your body. You're basically coated in pollen. If I take a walk through Central Park right now and I come in, I'm coated in multitudes of pollen. So just getting that off of you, if you happen to be pollen allergic, is a great idea. The treatments that we have for allergy are not great until recently. They've been the same for approximately 200 years (laughter). There hasn't been much advancement in allergy treatments. And avoidance or stopping the reaction before it even starts is the gold standard. So - but that's increasingly difficult. Like, where are you supposed to go if you're allergic to tree pollen? I mean, I guess you could move to the desert. But even, as I discovered when I was researching this book, the desert, they have their own problems right now - I mean, Bermuda grasses and certain trees that we've imported into the desert. So there really isn't anywhere to go to escape some of our allergy problems or allergens.

DAVIES: Yeah. Plus, we love trees. You know...

MACPHAIL: Yeah, exactly (laughter). I know. I don't want to sound like I'm down with trees (laughter).

DAVIES: Yeah.

MACPHAIL: I love trees.

DAVIES: Somebody pointed out that in some cases, municipalities, when they import and plant trees, will plant all - do I have this right? - all male trees. And this can create a problem. Are you aware of this?

MACPHAIL: Yes. So because female trees, they tend to be messier. So they have, you know, seeds falling and things like that. So they're harder to clean up after. And so for years it was thought, oh, well, let's just have the trees that don't have that problem, except that they're pumping out pollen to pollinate the female trees (laughter). And so you accidentally get this imbalance of pollen-producing trees that I'm not actually sure - one of the most interesting things is that I couldn't get anyone from any parks department to talk to me. I - because I wanted to know, do you still plant the same way, like, if you're planting trees now? I constantly am seeing new trees being planted in my neighborhood. And I want to know, are these trees that produce a lot of pollen? Like, have you thought about that? And I couldn't get anyone on the phone, so I have no idea if we're still making the same mistakes. Probably yes.

DAVIES: Let me take another break here. Let me reintroduce you. We are speaking with Theresa MacPhail. She's a medical anthropologist who writes about global health, biomedicine and disease. Her new book is "Allergic: Our Irritated Bodies In A Changing World." She'll be back to talk more after this break. This is FRESH AIR.

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DAVIES: This is FRESH AIR. And we're speaking with Theresa MacPhail. She is a medical anthropologist who writes about global health, biomedicine and disease. She has a new book, it is "Allergic: Our Irritated Bodies In A Changing World."

A few other things I wanted to get to - you know, seasonal allergies can be annoying, but are there long-term effects from dealing with them or treating them, you know, year in, year out?

MACPHAIL: Yeah. One of the most interesting things when I was researching this book is - so I would ask to talk to regular people about their allergies. And everyone initially was like, why do you want to talk to me about my hay fever? That's so weird. And I was like, well, I want to understand how you live your life with it. And it was almost like being a priest because once they got talking, it was like I was in a confessional booth. And these things really do affect the quality of people's lives. I - that is something that I absolutely learned in the five years I was researching this book. It doesn't matter if it's a mild allergy to a severe allergy, everyone's basic quality of life suffers when they have an allergy.

You're spending - first of all, you're spending a lot of money on treatments. So you're taking Zyrtec or whatever you're taking, your antihistamines. You're buying them. You're taking them on a regular basis. You're buying air purifiers. You're doing all of these things. You're buying allergy-free foods if you've got food allergies. You're spending a lot of money. The second thing is, is you just don't feel well. You don't feel at your best. So most people with mild allergies don't sleep well. So their sleep is affected, which means they're not as productive. Their mental health suffers. Like, most people with a moderate allergy have some form of depression or anxiety. We can say that that's correlation and not causation. But if you're constantly lacking sleep and you're constantly not feeling your best, that - it takes a toll after a certain amount of time.

DAVIES: And does it grind down the body in any way physically? Or do...

MACPHAIL: Absolutely. I mean, people that have allergies, seasonal allergies especially, you're more likely to get sick, because think of it as - say, you're at a gate at Yankee Stadium. And your immune cells - like, we're back to the bouncers. The bouncers are there. Everybody is there trying to stop viruses from coming in. If you're being - if millions of oak pollen particles are trying to come in and you're dealing with them, are you really going to spot the SARS-COVID virus when it comes in? No. Your immune system is distracted. It's - it can only do so much. And so if it's busy responding to one thing, it could lead to you missing something else.

So we really want healthy immune systems. That being said, I will say a little positive. There's not much positive here (laughter). One of the things I'm really aware of is when I talk, it can sound pretty depressing. But people with allergies, actually, you should feel happy because your immune systems are strong and functioning. And it turns out that people with allergies actually can have lower levels of certain cancers, like gliomas, partially because your immune system is so strong. And it's on the alert. So there's downsides, but there's a small upside.

DAVIES: You know, it's - in the book you say that in some way, maybe, you embarked on this quest to study allergies because of your father's death to the anaphylactic shock from a bee sting. And heaven knows you learned a lot. I mean, do you feel that you came away with any particular new perspective or insight about his death?

MACPHAIL: I do. I started off simply wanting to know, why him? So millions of people are stung by a bee every year, but very, very, very few of them will die. And so I really wanted to understand why. And I think with any tragedy, that's the case. But what I ended up learning throughout the research is that there are so many things that intersected that led to my father's reaction. You know, he had his window down because he was smoking - and why was he smoking? - because he was stressed. And why was he stressed? Because he was trying to make a living in a capitalistic society.

And, you know, stress had a lot of role to play in how he ate. So he didn't take particularly good care of himself. He drank too much bourbon and ate too many steaks. And so, you know, those kinds of factors really are at play. And we are really all interconnected. And so I think, by the end, I had realized that allergy is an individual biological problem, but that's not all it is. It's also a community problem and very much deeply a social problem.

DAVIES: Well, Theresa MacPhail, thank you so much for speaking with us.

MACPHAIL: Thank you. I've enjoyed it.

DAVIES: Theresa McPhail is a medical anthropologist who writes about global health, biomedicine and disease. Her new book is "Allergic: Our Irritated Bodies In A Changing World." To keep up with what's on the show and get highlights of our interviews, follow us on Instagram at @nprfreshair.

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DAVIES: FRESH AIR's executive producer is Danny Miller. Our senior producer today is Roberta Shorrock. Our technical director is Audrey Bentham. Our interviews and reviews are produced and edited by Amy Salit, Phyllis Myers, Sam Briger, Lauren Krenzel, Heidi Saman, Therese Madden, Ann Marie Baldonado, Thea Chaloner, Seth Kelley and Susan Nyakundi. Our digital media producer is Molly Seavy-Nesper. For Terry Gross and Tonya Mosley, I'm Dave Davies.

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