Rachel Feltman: For Scientific American’s Science Quickly, I’m Rachel Feltman.
An estimated one out of every 10 people in the U.S. has some kind of food allergy, which adds up to more than 33 million Americans. Peanut allergies are among the most common and certainly take the lead as the most visible.
But peanut allergies weren’t always so prevalent. In the late 1990s a nationwide survey found that peanut allergies were reported in 0.4 percent of American children. Just over a decade later that number had more than tripled.
On supporting science journalism
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Scientists still aren’t completely sure what led to this big uptick, but it could stem in part from parental anxiety over peanut allergies—and misguided advice about how to keep kids safe.
Here to tell us more about the latest research on peanut allergies, including new avenues for treatment and prevention, is Maryn McKenna, the author of a recent article on the subject for Scientific American. Maryn is a journalist who covers food policy and public health.
Thank you so much for coming on to chat with us today.
Maryn McKenna: Thanks for having me.
Feltman: So what do we know about the origins of peanut allergies?
McKenna: This is a really interesting mystery still. No matter how much study and how much research funding has gone into the problem of peanut allergy—and food allergies more broadly—a lot of it still remains kind of opaque.
Feltman: Mm.
McKenna: We know the biological mechanisms of what makes an allergy happen, but why peanut allergy in particular came on the scene 20, 30 years ago or so and why it blew up to such a major public health problem—people are still working that out.
Feltman: So I guess let’s start with the easier question, then, which is: What is a food allergy? How does it work, both genetically and in the moment in a person’s body?
McKenna: I think most people are familiar with the concept of our having an immune system that, through a variety of mechanisms, defends our bodies against the outside world, broadly speaking—against things that are not us. Most of the time the immune system works really well to adapt its reactions, its defenses of us, to the way we continue to live our lives.
Sometimes its reactions get wildly out of scale, and that’s what happens in food allergy and peanut allergy. The immune system recognizes proteins in these foods as being sort of not self, not part of us, and mounts an extraordinary reaction that expresses itself in the kind of symptoms that, if you’re allergic, you’ve experienced or that you may be familiar with from hearing about them from other people: hives, itchiness, difficulty breathing, difficulty swallowing; in the worst presentations depressed blood pressure, inability to breathe and sometimes, in, in the worst case, a heart attack.
Feltman: And what are the actual rates of nut allergy? It’s definitely one of the ones we hear about a lot, but how prevalent is it?
McKenna: This can be a frustrating question to try to answer because what we know about people being allergic depends on their telling researchers that they’re allergic …
Feltman: Mm.
McKenna: So it’s all self-reported. There are biological markers for allergy, but we don’t apply tests for those biological markers to the entire population, so all of the data relies on people telling researchers who have asked that an allergy is present in themselves or in their kids, if they’re parents answering for children.
All of that said the numbers are really big. It’s estimated that one out of every 10 individuals just in the United States has some kind of food allergy …
Feltman: Mm.
McKenna: That’s more than 33 million people. And one of the folks I spoke to for this story said: “If you think of the average size of a classroom in elementary school, for instance, that means in every classroom two to three kids are going to have food allergy …”
Feltman: Mm.
McKenna: And peanut is one of the most common food allergies. It’s actually probably not the most common, but it tends to be the one that we hear about the most: if we have kids in school and they’re aware that in, in the lunchroom there’s a peanut-free table, or if you get on an airplane and realize that you can’t have peanuts on the airplane because there might be an allergic person on the plane with you that day. So peanut’s very sort of front of mind …
Feltman: Mm.
McKenna: For a lot of people.
Feltman: Yeah, and why is that? Why do you think it’s the one that we hear about the most? Is that to do with the, like, typical degree of the allergy?
McKenna: The funny thing is that, according to the best data, the number-one food allergy, the most commonly experienced food allergy in the United States, is actually against shellfish …
Feltman: Mm.
McKenna: And it affects, in the most recent data, more than eight million people, whereas peanut and milk allergies, which are two and three, affect a little bit more than six million. But most people don’t stroll around their lives eating shrimp, right?
Feltman: [Laughs] Sure.
McKenna: This is not a thing that, for most of us, that we munch walking down the street or eat in a protein bar. But peanuts are incredibly portable, they’re a favorite food for kids—peanut butter is pretty much ubiquitous, and so peanuts are just present in our lives a lot.
But why peanuts cause such reactions is one of those enduring unanswered questions. There are a lot of hypotheses advanced for why that is, ranging from the way that allergy happens in general; that there are things in the environment that are more present than they used to be or that the environments that we grow up in are cleaner and so we tend to overreact to them; to the ubiquity of ultraprocessing in food, which might be distributing these proteins more broadly so that kids are exposed to them when they aren’t aware that they’re exposed to them; or it could just be that we like peanuts [laughs].
Feltman: [Laughs]
McKenna: But as a result, for all of those reasons and probably others as well, peanut allergy is very present in the lives of families, and it can be very serious.
Feltman: And speaking of the top food allergies in general, what are the “big eight”?
McKenna: So the “big eight,” that’s an actual legal term, and it indicates the allergens, the proteins, that are present in food that, when it’s a processed food, have to be declared …
Feltman: Mm.
McKenna: On the label. Up to 90 percent of food allergies are caused by these eight things; that’s why they were made the subject of legislation back in 2004. So peanuts, milk, eggs, fish, shellfish, tree nuts—so things like almonds, for instance—wheat and soybeans, and there’s actually a ninth, a sort of footnote to the “big eight” that was added just a few years ago, which is sesame.
So those nine allergens are responsible for an enormous amount of food allergy in the United States, and sometimes they’re linked allergies, like someone who has an allergy to peanut might also be allergic to egg or to milk, but as a category they cause a great deal of distress.
Feltman: And I know you touched on this a bit a minute ago, but how much do scientists know about how we got to the point we are now with food allergies? Why are they so prevalent?
McKenna: The question of why food allergies, and peanut allergy within that, is so common and seems to be getting more common, at the base—like, why this starts—is still really an unanswered question. But that it’s increasing, no one disputes that.
You can go by some sort of qualitative measures, like if you are an adult who’s been flying on airplanes for 30 years, 30 years ago you might have been able to have a peanut snack inside an airplane, and you would not have heard a member of the cabin crew saying, “If you brought peanut snacks on board, please do not eat them because there’s an allergic person sitting somewhere near you.”
A set, a sort of nested set, of surveys of the population done over a couple of decades made it really clear how food allergies are increasing. The first was done in 1997; these were all done by researchers at Mount Sinai School of Medicine in New York City. And 11 years from the first study—1.4 percent of kids in the U.S. were allergic to peanut. So that’s a threefold increase across just 11 years, starting in the late 1990s. That’s really remarkable.
Feltman: Yeah. So your piece really focuses on treatments. You know, even with all the remaining uncertainty around peanut allergies, what did you find out about where science is making the most progress and how they’re doing that?
McKenna: Reporting this story was really a journey because I went into it being interested in one particular therapy that had been advanced just a [few] years ago. It was the first [Food and Drug Administration]-approved therapy …
Feltman: Mm-hmm.
McKenna: For peanut allergy, not a cure—a method of desensitization. This method of desensitization is a drug called Palforzia, and what it actually is, is minutely powdered peanut protein …
Feltman: Mm.
McKenna: That’s given to kids in very precisely measured doses by mouth over a period of time, and it’s meant to desensitize them. I was interested in it because I felt that it hadn’t done very well in the marketplace, and I wasn’t sure if that was because of the dosing regime or because it happened to be introduced to the market at the start of COVID, but I wondered, “If this [allergy] was such a big problem, why hadn’t this [medication] taken off?”
So I started to look at this, and it turns out that there was a bunch more science that I was not aware of. And this one particular FDA-approved therapy, Palforzia, was only a small part of the story.
Feltman: Hmm.
McKenna: So the bigger story is that there have been really remarkable advances in desensitizing people to the allergy …
Feltman: Right.
McKenna: So that they can go from being in danger of anaphylactic shock to actually being safe to eat a small amount of peanut or peanut protein or peanut butter. And exactly how small that small amount is depends in part on how allergic they were to begin with.
Some people have been made relatively safe from accidental exposures …
Feltman: Mm-hmm.
McKenna: Like cross-contamination in food manufacturing. Some people who were less allergic to start with have actually been made safe enough to be able to eat peanuts or peanut butter if they want to.
Feltman: Wow.
McKenna: Now, some researchers in this field will say, “Well, you still aren’t getting all that far. We are making people safe in their lives, but they still have to be careful about what they’re eating; they can’t go face first into a jar of peanut butter.” And therefore, I found as I was working on this story, there are other really interesting efforts going on to try to keep the allergy from developing and to effectively nullify the allergy once it has developed. And those are sort of like the far horizons of food-allergy science, [but] as it says in the story they are things that people are beginning to explore.
Feltman: Yeah, what’s your sense of where things are going in the next few years?
McKenna: So right at this moment a clinical trial is starting that is really unusual, and it’s extremely early days; they are getting to just a phase 1 at this point—only one patient has actually been reported out. But what it does is it uses a combination of drugs made by a company called Regeneron, to essentially reset or rewrite the body’s understanding of what it’s supposed to react to.
And there was research into the effect of one of these drugs; the name for it is Dupixent. And researchers gave this drug and then tested people with their allergy, with the food they were allergic to, which was peanuts, and discovered that though it seemed promising it didn’t actually have a long-term effect.
And then they decided to try adding in a second drug, which has just been approved for a particular cancer, a cancer of the cells that make the antibodies that cause the body to overreact in an allergic situation. They believe they can use that combination to cause the body to forget that it’s overreacted to a particular thing …
Feltman: Hmm.
McKenna: To essentially set the allergy back to zero—again, very early. But if that trial, which will take a number of years, if that trial proceeds, that’s a really promising avenue of inquiry.
The other thing that’s really interesting and that’s beginning to get traction is that there is a school of thought based on a set of studies that were done in England that asks: Well, maybe food allergy, especially peanut allergy, maybe it’s kind of our fault because maybe we, as a society, are not introducing children …
Feltman: Hmm.
McKenna: When their immune systems are developing to peanuts at a time when their immune systems could handle them and not overreact to them.
And where this came from was an accidental finding by a British pediatrician who was speaking to a group of pediatricians in Israel and asked them how many of them were treating food-allergic kids, expecting every hand to shoot up …
Feltman: Mm-hmm.
McKenna: And in fact, almost no one did. Very few people in the audience were actually treating allergic kids. And this was a fascinating difference between the U.K., where the scientist had come from, and Israel, where he was speaking at the time.
And through a set of very clever experiments they discovered that the difference was that there’s a ubiquitous snack in Israel called Bamba. That was what …
Feltman: Yeah, it’s also ubiquitous in Germany [laughs] …
McKenna: Oh, interesting.
Feltman: I love Bambas, yeah [laughs].
McKenna: So they, they—there’s—here in the United States, in Trader Joe’s, they make a Bamba equivalent; I saw it the other day.
So Bambas are kind of—for people who have not experienced them—Bambas are kind of like Cheetos. They’re a puffy, extruded product, but instead of cheese on the outside they have peanut butter on the outside. And they’re very light and wispy, and they collapse, and they’re easy to chew; they’re not as tough as a Cheeto.
And Israeli kids, it turned out, get them quite early in life, and so they were getting an exposure to peanuts at a time when the British kids were being held strictly away from peanuts …
Feltman: Mm.
McKenna: Because that was the dominant advice at the time—this is just a few years ago—for any child in a family with a history of allergy was: keep them away from allergenic foods.
And so this pediatrician who led the study, Dr. Gideon Lack, proposed that if we sort of abandoned our current guidelines, if we started to introduce kids to peanuts very early—which takes some doing because they have to be introduced to solids in time to be able to swallow peanut butter or peanut powder safely—then it seemed likely that they would be at less risk of developing allergy.
And, and his research proved that was correct. And now the public health establishment and pediatrics and pediatric nutrition are struggling with this conundrum of the excellent advice that seemed to keep kids safe for so long may actually have set some kids up for allergy instead …
Feltman: Mm.
McKenna: And how do we implement the new findings now that they exist?
Feltman: Yeah, that’s really interesting. My last question is just that, you know, you were really careful with the word “cure” in your story for Scientific American, but do the [researchers] that you talk to seem to think that that’s a possibility in the future?
McKenna: Everyone is extremely careful around the word “cure” in this situation, and I respect that. They’re careful about it for a couple of reasons.
First, even the most optimistic researchers to whom I spoke are clear in saying that when they do these various new modalities of desensitization, that’s all they’re doing; they are not curing the allergy, but they are making it safer for people to live everyday lives.
And the second is: these other avenues in which the allergy might actually be remodeled, those are such early days that whether it’s actually going to work in broad populations, either the very early feeding or this drug administration, it’s way too early to make confident statements about them.
But I think, also, the reason that they’re so careful about this word “cure” is because there are so many families out there—you know, families of millions of kids in the U.S. have had their lives disrupted by food allergy, especially peanut allergy. It really profoundly changes the life not just of a child, but the life of a family.
Feltman: Mm.
McKenna: And therefore, families are very eager for something dramatic to happen, and no one wants to overpromise. Even though they believe they see real hope coming over the horizon it’s too early for them to say with confidence that it will really change the game.
Feltman: Thank you so much for coming on to talk us through this story. I’m sure our listeners will enjoy checking it out in the magazine.
McKenna: I hope they read it. Thank you so much for having me.
Feltman: That’s all for today’s episode. We’ll be back on Monday.
Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Kelso Harper and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.
For Scientific American, this is Rachel Feltman. Have a great weekend!
