Why is everyone getting food allergies?
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Megan Cruz grew up eating tons of shellfish. I'm from Shreveport, Louisiana. So we have lots of crawfish and seafood and all the shrimps.

And she particularly loved it on special occasions. So for my 21st birthday, I decided I would get all the seafood. So that's what I did. Go pick out all my blue crabs. I'm so excited. We have like five pounds. Megan boiled the crabs in some water with a splash of orange juice and sat down to eat with her husband.

I was sitting there eating my crab. Totally, everything was fine. I was happy. I have my daiquiris, living my best life. But pretty soon, she started feeling kind of weird. I started getting really itchy for a second. And I think I went to go pee.

And then when I went to go pee, I like pulled down my pants and there's welts all over my legs and all over my body. And I realized that something was wrong. And so I was like, I'm going to take a shower. That seems like a good option to do. Turns out you're not supposed to take a shower because then everything started to get worse.

And then I like came out to my husband. He's like, why do you look like that? And I'm, I don't know why I look like that. Why am I turning purple? What is going on? They didn't know what to do. So they decided to get to the hospital as fast as they could. He's like speeding past these lights. I was feeling really lightheaded and I felt like I might pass out. But I was also terrified to pass out because I was like, what if I don't get to the hospital in time?

They finally got there, and it was basically a ghost town. It's like midnight. It's the graveyard shift. No one really wants to be there. And then I'm getting admitted, and I'm just trying to like, I like walk up to the lady, and I'm just like, hi, I think I'm having anaphylaxis. Like almost blue in the face, but also I'm panicking on top. Anaphylaxis is a full body response to an allergy.

Symptoms can be different from person to person, but typically the throat swells, making it hard to breathe, blood pressure drops, and the heart rate shoots up.

People can die from it. And when the doctors finally saw Megan, they were floored. So then they called the med students in because they were like, "This is the worst thing we've seen. The worst case of anaphylaxis." I'm like, "Come in. Let's go, you know? It's my birthday. It's a party at this point, right?" The nurses eventually got some epinephrine — that's the stuff in an EpiPen —

And they gave it to Megan through an IV to stop the anaphylaxis. My doctor asked me, he's like, "So what'd you eat?" And then I told him and he's like, "Oh, shellfish. Well, how often do you eat that?" And I'm like, "All the time." So he was like, "Well, I'm guessing that's probably what caused it, but it was just very odd because I've ate it my whole life." Megan couldn't remember having food allergies at all as a kid. I don't, I can't even tell you how much random stuff I ate. I never died then. And now Megan's not just allergic to shellfish,

She can't eat peanuts anymore, or garlic, or a whole bunch of other foods she used to love. I had relatively 22 allergies erupt around the age of 21. But Megan's not the only one who's more allergic than she used to be. According to allergist Scott Citrer, more and more people, both kids and adults, are developing allergies.

Come on, you know, if you're someone who's over the age of 40 or so, you were a kid in school, your friends didn't really have food allergies. You have kids now. Oh, my gosh. You know, like several kids in the classroom have food allergies. I mean, that's sort of like, you know, you don't have to be a scientist to say, hey, wait a minute. It's not really a question that there has been an increase. The question really is why?

I'm Noam Hassenfeld, and this week on Unexplainable, why are so many more people getting food allergies? And is there anything we can do about it? Okay, Umair Irfan. Hello, Noam. You've been reporting on the rise in allergies for Vox.

Before we get to the rise itself and what's going on over there, let's make sure we just have our basic concepts in order here. What exactly is an allergy? An allergy is like a false alarm in the immune system. It involves a very particular mechanism that scientists think that we evolved to help us deal with parasites. These are things like roundworms and hookworms. But occasionally, it seems like the immune system can get confused. It can go from targeting parasites to targeting peanuts.

And then as a result, the immune system starts doing all these things that can actually be harmful to you. So I talked to Scott Satura about this, who we heard from at the top. He's a pediatric allergist at the Mount Sinai School of Medicine. And he told me that the responses can range widely from things like rashes and hives all the way up to anaphylactic shock. And that can send you to the emergency room. It's totally counterproductive. I mean, why should I be eating something and I all of a sudden swell up, can't breathe? You know, that seems kind of ridiculous. Right.

But this is the same system, the same immune components that fight parasites. So you're basically saying that an allergy may have developed in response to something that is actively harmful. But at this point, you know, with something like peanuts and shellfish, someone going into anaphylactic shock from, say, shellfish is really just their body turning on itself. Well, not the body turning on itself. That would be an autoimmune disease. This is a body turning on itself.

an outside source of an allergen that is otherwise benign. So autoimmune diseases actually have a slightly different mechanism. With an allergy, your body is turning on something that's foreign to it, but benign. And that's because your immune system has this very delicate task of trying to sort what is part of you and what is not part of you. But they also have to sort the gray area as well. These are the things that are not part of you, but are harmless. And these are the things that are not part of you that are harmful.

And so the immune system learns to recognize dangerous pathogens and ones that can live with us and may actually be beneficial to our immune system. And that's actually a little bit trickier. And in that gray area, that's where the immune system can get scrambled. And that's where we see allergies arise. They start overreacting or start treating something as harmful that is otherwise actually harmless. So if peanuts are harmless, like how does the body start getting tricked into thinking that they're harmless?

Like, how do you actually start getting allergic to peanuts or shellfish or something like that? Right now, we don't really have a good answer for that. And scientists are hard at work trying to find out. It's an important mystery because we're finding that more and more people are becoming allergic to peanuts and to shellfish. And they're having some very severe allergies. So the health burden from allergies is actually increasing.

So how much have allergies actually gone up recently? The conventional wisdom here in the U.S., maybe going back to the 90s, was that in textbooks you'd see that about 4% of kids had food allergies, maybe 2% of adults. The thinking was that kids would grow out of their allergies as they got older. But now the studies from the U.S. and other locations are saying that it's more like

eight or 10% of children and around the same percentage for adults. Huh. So a little bit higher in kids and like a lot higher in adults. That's right. And, you know, in some instances we're talking about on average, you know, roughly one in every 13 kids has a foodborne allergy. Whoa. That's like two kids per every classroom. So when we're talking about allergies going up, do we know if this is more people being born with allergies or more people developing allergies over time?

It seems to be a mix of both. Doctors are finding that more children are being diagnosed with allergies as babies and as toddlers and so on. But more adults are also reporting that they're becoming sensitive to foods that they weren't sensitive to before. So it seems like we're seeing both an increase in people born with allergies and people acquiring allergies later in life.

Do scientists have any idea at all why this is happening? Like, why allergies are going up so much? Well, one of the best guesses and the one that seems to have the most support behind it is this idea called the hygiene hypothesis. Okay. You know, remember how I said earlier that this was a mechanism in your immune system that's used to deal with parasites?

Well, as we've developed as a society in the U.S. and around the world, as we've improved sanitation and, you know, spending even less time outdoors, we're less likely to be infected by parasites. You start living in houses. You start being able to protect yourself with antibiotics, with vaccines. You start eating food that is clean. It comes in a can. You're using a dishwasher that really cleans every speck of dirt from your dishes. And your immune system is seeing a very different pattern of

And so without these opportunities to be infected, this part of the immune system stays revved up in some people, and then it can turn on more innocuous things. For example, the danders in our pets or the pollens in our air, or in this case, the proteins that are in our foods.

And so we've seen allergies rise with development in countries as sanitation has improved. We see lower rates of allergies in people who live in rural areas, but higher rates in people who live in urban areas. And so there seems to be this very strong association with a heightened level of cleanliness and sanitation and allergies. This is like the general idea behind, I assume, parents who want to be like, oh, we have a kid, like, let's put him on the subway and have him lick a pole.

I mean, don't lick a subway pole. That's gross for a number of reasons beyond allergies. But yeah, there is this idea that maybe being in a less hermetically sealed environment early in life may be beneficial. And now more scientists are actually advocating for a graduated and deliberate way of exposing infants and toddlers to potential allergens. But if hygiene theory is responsible for the rise in allergies here, like why is this so

only happening now. It's not like we didn't have sanitation in the 90s. You're right. Sanitation has been improving for hundreds of years, and we've been seeing this in many parts of the world. So why are we seeing such a big pickup now in the past 20 to 30 years? That's not entirely clear. And for something like allergies, it's pretty likely that there are multiple factors at work here. So even if the hygiene hypothesis seems to be the strongest theory, there might be some other element that is playing a role here as well.

So if this hygiene theory doesn't explain the rise in allergies on its own, what are some other factors that might be contributing here? One idea that scientists are looking into is the timing of food exposure. For instance, this idea that perhaps if a baby is vulnerable to developing allergies, they should not be exposed to foods that could potentially trigger those allergies. Don't give that baby milk protein until age one, egg until age two, peanuts, tree nuts, and fish until age three.

And that was well-intentioned, but it didn't have a lot of research behind it. But now the thinking has almost completely reversed, that if you are at higher risk of allergies, it might be a good idea to expose these babies on a very slow, graduated basis, deliberately early in life. Ingesting the food lets the gut immune system see it and learn about it in a positive way. Like, this is something that's nourishment for me.

And that will help desensitize them. Whereas if you're not eating it, it's still in the environment, meaning that there's still milk in the environment, there's still egg in the environment, there's a peanut around you. All of those proteins that should have been in your mouth are instead all around you and on your skin, and it's hyping up an immune response that's counterproductive.

Then if you were waiting until you're one or two to eat it and you then ate it, it's too late. Your immune system already learned to fight that protein that it should have learned to accept by eating it early on. And so that's one other theory is that the timing of when we're exposed to certain types of foods and allergies, potential threats is changing in the modern world. And if we change the timing of that exposure, that could help counteract that trend.

So it seems like hygiene theory combined with some of this timing of food exposure could explain a lot of this rise in allergies. Are there reasons to be skeptical of both of these theories together? I mean, they do seem to explain a lot, but they don't, again, explain everything. What do you mean? Well, for one thing, why are adults then developing allergies as well? Right. Adults and children sometimes are becoming sensitized to the same things.

So what is at work there? Is there a common environmental exposure, for instance, that might be making people more vulnerable to allergies? Yeah, it seems like hygiene theory and food exposure...

are all about kids having allergies. Are there any ideas about, you know, what's behind this rise in adult onset allergies? That's also a big mystery. You know, there's a few ideas that scientists are studying as well. One is this idea that perhaps in a post-infection state, like maybe if an adult got sick with the flu or some other serious illness,

In that period after the infection, their body's immune system might be recalibrating and in that phase end up targeting something that is otherwise harmless. By post-infection state, you mean sort of like after COVID or someone that might have long COVID, like these lingering symptoms? That's right. You know, even with influenza and many of these other common infections that we see,

We're starting to appreciate more that they can actually have symptoms that last for a long time, even after the virus or the bacteria that caused the illness has been defeated by the body. Perhaps that's playing a role in adult onset allergies as well. Like maybe you had an illness, you got better, but your immune system in that phase got redirected into targeting something that really it shouldn't be targeting. But beyond that, I mean, I think scientists are trying to be open-minded here and just see what else is at play.

So we've got all these possible explanations here. What makes this so complicated to solve? Like, what are scientists still wrestling with? For one thing, it's really hard to isolate any one of these variables because, you know, when we talk about allergies, they do affect individuals. But when we're talking about the rise in allergies, we're talking about something that's happening across tens of thousands, if not millions of people. And there are so many different other variables that are at play as well. You know, the environment that they live in, their genetic susceptibility,

other kinds of environmental exposures, other kinds of sociological exposures as well. So scientists want to have a little bit of humility here and say that, you know, we don't fully grasp all the things that are at play when it comes to these allergies. After the break, just how allergic are we going to get? Is everyone going to get allergic to everything? That's coming up next. Support for Unexplainable comes from Greenlight.

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Umair, we're back. Hey, Noah. So how should I wrap my head around exactly how bad this rise in allergies is? Like, are we all going to just get more and more allergic until everyone has allergies? To answer your second question first, the answer is no. Scientists don't think that we're all going to get allergies. And if you don't have allergies right now, the researchers that I talked to told me that you really shouldn't lose sleep about it.

most people don't develop allergies as adults. And the ones that do, they're just one part of this rise in overall allergies we're seeing in the population. Now, while allergy rates are going up, it does appear that in some circumstances that it's reaching a plateau. It seems to be leveling off when it comes to certain types of foodborne allergies.

And that sort of indicates that there might be just an upper limit to how many people in the population are susceptible to developing allergies. So if we're getting to this plateau, why should we be worried? Is the problem just kind of solving itself? A plateau means that it's staying level. It's not going down. We're talking about close to 33 million people in the U.S. having food allergies. That's about one in 10 people.

So even if that rate holds steady right now, that's a huge health burden, especially for families with kids. You know, that costs them about $25 billion per year. And not only that, like your quality of life goes down. Like imagine being paranoid about eggs being in anything because eggs are used to make everything. Soy is used to make everything. Peanuts are used to make everything. And again, people still die from allergies as well. Like people with severe anaphylaxis do die. It's not in huge numbers, but it can be fatal. And

knowing that that's a possible outcome adds to the stress of dealing with it. And, you know, we're talking everyone from little kids to adults. And so this is a pretty common experience that is, you know, becoming increasingly more common. And then let's just say you do,

develop adult onset allergies or, you know, if you're just one of the unlucky children that seem to be born with more allergies today, like what are you supposed to do? Are these things that can be cured or are these things that just have to be managed? Right now, the big thing is management. With foodborne allergies, I mean, the best thing is to simply avoid the food in most circumstances. Just try not to eat it.

Beyond that, there are some experiments going on about how to use techniques like immunotherapy. And I talked to Ruchi Gupta, this pediatrician and allergy researcher at Northwestern University, and she described this process by where you gradually introduce somebody to a food that they're allergic to over time in order to build up a tolerance. Under an allergist supervision, you slowly up-dose until you can tolerate a certain amount of peanuts. And then...

You keep that amount in your diet so that your body keeps recognizing it. That would sort of be like an allergy vaccination almost, like give you a tiny amount of peanut and kind of vaccinate you against peanuts. Is that is that a wrong analogy? I kind of I mean, I mean, you are talking about, yeah, like introducing the immune system to something. But like with a vaccine, you're teaching your immune system to fight something, whereas with this, you're trying to teach your immune system that it's harmless. Right.

Also be like a reverse vaccine. Yeah, basically. Yeah. You're trying to basically like tell the immune system, hey, this stuff is friendly. It's harmless. Don't overreact. Take a deep breath. But beyond that, there isn't really that much to do because we don't really know how to cure an allergy per se.

So if there's no way to cure it, is there any way to prevent being allergic to something? There isn't, as far as we know, for adults. But I mean, for young infants, it does seem like the earlier exposure to certain types of allergens does play a role. You know, there was this study that was done in the UK called the LEAP study. It was a landmark study where their theory was, OK, maybe if the immune system sees this food in that first year of life,

they're getting used to it and they don't have the allergy. They did a randomized control trial of infants and they exposed them to peanut proteins. They found that incorporating these peanut proteins into some of their food, into their baby formula, in their diet early in life, that led to a much lower rate of peanut allergies. They decreased their development of peanut allergy by 80%. What's exciting about that is knowing that if we

counsel new parents for their babies correctly, and they start peanut products and potentially other food allergens early in life, their immune system recognizes it and does not then go to fight it. So that's a part of the challenge here is figuring out what to introduce babies to and when. And if you can do that, then maybe you can help stem this rise in new allergic reactions in kids.

So is this, are we calling for like a peanut AmeriCorps, like mobilize the country, get tiny amounts of peanuts to all babies across the country? Not quite. You know, it's not as though we can make a categorical recommendation across the board because allergies are very particular and very specific to individuals.

So while we are seeing a society-wide increase in them, the way they manifest in individuals is very unique. A lot of researchers say it's worth getting diagnosed, worth actually seeing an allergist and figuring out what your reaction was when you have a bad reaction to a food because it may not necessarily be the case that you have to avoid it forever. The more you know about what you have, the more you know how to manage it.

So when we've got this collective public health problem that's based on a bunch of hyper-individualized responses to allergies, what are we supposed to do? How are we supposed to solve a problem like this? I mean, you can approach it from multiple angles because like you said, this is a problem which has many different roots and thus requires many different solutions. And so one is trying to

to inoculate the individual, trying to make them desensitized to them, to the allergen to begin with, and trying to head off the allergy, preventing it from beginning. And then if they do develop an allergy, to minimize exposure, so to make sure that they're not being exposed to something dangerous, and to make sure that their symptoms can be easily mitigated, and that people know, for instance, if they see a severe allergic reaction, how to use an EpiPen if they do see somebody with an allergic reaction, and building a culture around that.

So if you see someone and they're turning purple and they can't breathe and like, you know that they're not choking, check them for the EpiPen. And do remember that it's blue to the sky and orange to the thigh. Megan, who talked to us about her seafood allergy at the beginning of the episode, she told me that going out to eat makes her nervous that the wrong exposure could land her in the emergency room again. It's like Russian roulette. You never know. Something could happen. It's a waiting game.

in the foreseeable future, allergies are here to stay. And we might not know fully why these allergies are on the rise, but to whatever extent that we can mitigate allergies to reduce their harm on individuals and help the people with allergies live productive, fruitful, and

like non-anxiety inducing lives, then I think that is a worthwhile endeavor. No one chooses to be allergic to a whole bunch of things. I promise, like me and all my friends, most of us didn't have our allergies onset until we got older. So it's not that we don't miss the cinnamon buns. It's not that we don't miss the Reese's Pieces. It's not any of that stuff. It's that we can't for our health.

This episode was reported by Umair Irfan and produced by me, Manning Nguyen. There was editing from Catherine Wells, Brian Resnick, Meredith Hodnot, and Noam Hassenfeld, who also wrote the music. Christian Ayala did the mixing and the sound design. Zoe Mullick did the fact-checking. And somewhere deep in the woods, Bird Pinkerton found an old key inscribed with an octopus. Additional thank you to Alcus Toyas.

If you have any thoughts about this episode or ideas for the show, please email us. We're at unexplainable at Vox.com. And we'd also love it if you left us a review or a rating. Unexplainable is part of the Vox Media Podcast Network, and we'll be back next week.