Short Wave - A Surprising Culprit of Food Allergies

Episode Date: September 23, 2025

Food allergies have risen in the United States over the last few decades. Research suggests that 40 years ago the prevalence of food allergies was less than 1%. But today that number is closer to 6%. But this trend is not present in all countries — and what people are allergic to varies globally. Today, we dive into the complex world of food allergies with Dr. Waheeda Samady. She's the director of clinical research at Northwestern University's Center for Food Allergy and Asthma Research.Have a food science question? Email us at [e-mail] to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. When I was growing up, I was allergic to dairy. If I had a pizza or a bowl of cereal or ice cream, my nose would get totally stuffed up. In the scheme of things, though, it was just a mild allergy. There are other people that will describe like a sense of doom, almost, that kind of comes over them. This is Wahita Samadhi, the director of clinical research at Northwestern University's Center for Food Allergy and Asthma Research. Like the throat closing can definitely feel like they're breathing out of a straw. They can't take a deep breath.

And then the itching and the swelling kind of comes on very immediately. Nausea and vomiting are very common in all age groups as well. Just because it's like your body's trying to purge something that did not stay well with it. So it is a very wide range of experiences. But I think those who have extreme reactions describe it as just kind of like a whole body takeover. People can be allergic to all sorts of things, from bee stings to medicines. But what he did his specialty is food allergies, and their prevalence is exploding. We call it an epidemic because it really has risen dramatically over the last few decades.

So before the 1990s, the rate of food allergies in the U.S. amongst everyone was below 3%, maybe 2.5%. And just in children alone, research studies have found a dramatic increase over that time. Now we look at one in 13 children have a food allergy. That means allergy rates have basically doubled. But the strange thing is, this rise in allergies is not happening equally across the globe. The rise has definitely occurred in America, the Western Europe, Australia, and then parts of Asia and Africa. But no, there are definitely still places in the world where no one has a food allergy, no one's heard of food allergies. It's a very different experience.

Yeah. And interestingly enough, what people are allergic to is also very different. So that varies globally as well. But no, food allergies are definitely on the rise in certain countries, but not others. And do we know why? That is the million-dollar question, right? We have a lot of theories. Some of them are backed with significant amount of research.

Some are just emerging theories that people are trying to piece together. So today on the show, we try to answer that million-dollar question. One theory, you absorb the food through your skin before you eat it, and then your body decides it is something to attack. Plus, we find out what food allergies are, how they differ around the world, and why only some people develop them. I'm Aaron Scott, you're listening to Shortwave, the science podcast from NPR. So, Wahita, when somebody experiences an allergic reaction to food, will you zoom us in on what is happening on a biological and even a molecular scale. So the food, you know, goes into your stomach, it comes into your intestine, that food gets broken down, broken down, broken down to its basic proteins. And then it gets absorbed

into your intestine. Along the intestinal lining, you've got tons and tons of immune cells. And some one of those immune cells recognizes one of those foods because it's been previously programmed to label this food as something bad. And it sets off signals. We call them cytokines, but just chemicals. that just go through your body and it's like fight, fight, fight. It's basically telling your body an invader has come, we have to fight. And so that sets off multiple different cascades throughout the body. Some of it is to fight the invader. And some of it, some of these symptoms that you're having are just secondary to the inflammation

that the body is creating in order to fight this food that it's labeled as bad for you. So the swelling, for example, that you get in your throat when people have a very severe reaction, That's not really trying to fight anything. That's just secondary to the amount of inflammation your body has. One of the products of these chemical cascades is histamine, and that's why you get itchy, and that's why you get hives. And so what sort of tools do we then have to treat these reactions, and what are they doing on a molecular level? So that really depends on the type of reaction you have.

There are some reactions that are very mild. You have some swollen lips. You have a little bit of itching. have some hives or a rash, that can actually just be treated with antihistamines, and those will kind of stop those uncomfortable symptoms and kind of make the reaction go away. But if you have more severe symptoms, we really can't treat a severe reaction with just an antihistamine. So I'm talking about vomiting. If you're having any trouble breathing, your tongue is swelling or your throat feels like it's swelling. If you feel faint, these are all very, you know, indicative of a more severe reaction.

and that would require a medication called epinephrine, which is essentially adrenaline. So it will open up your airways. It will raise your blood pressure by constricting your blood vessels. The other interesting thing about epinephrine is that it will attach to some of those immune cells and stop the progression of an allergic reaction. But the way that epinephrine is given is through an injection. And that seems to be a hurdle for some folks who have food allergy. when you are in a severe reaction, nothing else is really going to take away the reaction or stop it from progressing the way up in effort and what? What do we know about why some people develop these food allergies while most people do not? So what we do know is specifically in children

that some children are at very high risk and one of the first signs that a child might be at high risk for developing a food allergy is that they have eczema. The earlier you develop eczema and the more severe the eczema is, the higher the risk of developing a food allergy. We think that there's a couple of reasons for that. One is, you know, eczema in and of itself is an allergic disorder. So when you're starting to have an allergic disorder, very early in life, it kind of signals that certain things in the immune system are a little imbalanced. So some people feel, and there have been studies that should look at children with eczema

and how different their gut flora is compared to children without, and there are significant differences. So these bacteria that have lived in our intestines for thousands and thousands of years, we feel like those have changed dramatically in the last 30 or 40 years because of what we're eating, what we're exposed to, certain species have become more dominant. And all of those microbes that live in our gut, they talk to our immune system. And so they might be kind of pushing things towards more of an allergic route. And then if we talk a little bit about one of the other major theories of why we think children are getting food allergies,

is that mislabeling that we talk about with food allergies, we feel very strongly that if you have a disrupted skin barrier and food particles are getting in through the skin, there have been really eloquent studies of testing. You know, if you eat peanut butter in the house, do you have peanut in the dust in your house? Yes, you do. There's peanut particles everywhere.

And so definitely food can get into a broken skin barrier. And when it does, you know, your skin is an organ. Your skin has a very vital role in protecting you. So all those immune cells that live in your skin, ready to fight any sort of invader. And if they're getting a lot of food proteins, they might label those food proteins as something bad and something the body has to fight. So that means the next time you're exposed to it, you're going to have a reaction. How do food allergies differ around the world, especially something with like peanuts, where it's present in some places,

not elsewhere, even within countries? So we know that within the United States, for example, food allergies will differ for different races in different parts geographically. It's not dramatically different, but there are some differences. Globally, for example, different countries will have different types of allergic foods. So in the U.S., you know, peanut is definitely high, egg, cow's milk, tree nuts, and then sesame has become common wheat, fish, and shellfish. If you go to other countries, for example, in India, lentil allergies are common, chickpea allergies are common. Not, again, India has far less food allergy than we do, but when they do have food allergy, it's to different foods.

If you go to East Asia, they'll have different types of shellfish and fish that they'll report allergies to. And so it definitely does vary. There's also thoughts about how we process our food. So, you know, the big question is like, why? Why peanut? Right, because peanuts are a leading allergen. Yeah, and it's a hard one to know. Like, I can't tell you I know the exact answer, but there have been studies that looked at how we manufacture peanuts now. So historically in other countries, peanuts are boiled.

Here they are roasted. And we do think that the roasting process itself makes peanuts, those proteins, just a little bit more likely to kind of set off an allergy as opposed to boiled peanuts, which people are eating in other countries. So if someone thinks they have an issue with a food, what should they do? Where do they start? Yeah. And I love that you're asking this question because there are so many people that think they have

one of these immediate type of reactions, and they don't. but they've been avoiding, like, large groups of foods. And some of these foods are just phenomenal sources of protein. And so what I would really recommend, and I know that there are definitely access to care issues, so I say this with some sensitivity, we really should try to find a health care provider that can help you get tested and at least be able to listen to what your symptoms are. Sometimes you don't even really need tests. You can tell someone what your symptoms are and they can tell you, okay, these are not

consistent with one of these immediate type reactions. Or there's also certain foods that can just kind of lead to histamine release, but they're not actually food allergies and you don't have to carry an epinephrine pen or, you know, some sort of injector with you. They're not those types and they will go away. There's other people who have allergies to things like pollen and when those pollens are on the foods, they can have little bits of reactions. So there's so many different things that could probably free you of thinking you have one of these severe, you know, immediate types of reactions and you can kind of walk freely knowing that you don't have them and kind of go by each day and also understand what kind of allergy you do have and what to do about it.

Well, Wohita Samadhi, it's been a joy talking with you. Thank you for taking time today. Thank you, Erin. Thank you for your interest. Before I head out, I want to thank our shortwave plus listeners by subscribing. You're supporting our show and making it possible to answer. answer questions like, where do allergies come from? And if you're a regular listener, we'd love for you to join, so you can also enjoy the show without sponsor interruptions. You are our community.

We cannot do this without you. Find out more at plus.mpr.org slash shortwave. This episode was produced by Burley McCoy, edited by our managing producer, Rebecca Ramirez, and fact-checked by Anil Oza. The audio engineer was Robert Rodriguez. I'm Aaron Scott. Thanks for listening to Shortwave from NPR.