A Surprising Culprit of Food Allergies

Summary

Podcast Summary: Short Wave – "A Surprising Culprit of Food Allergies"

Host: Aaron Scott
Guest: Dr. Wahida Samady (Director of Clinical Research, Northwestern University’s Center for Food Allergy and Asthma Research)
Date: September 23, 2025
Duration: ~15 minutes

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Overview

In this episode, Short Wave dives into the growing phenomenon of food allergies, exploring why their prevalence is rising, the biological mechanisms behind allergic reactions, and a surprising theory about how we may become allergic to foods. Host Aaron Scott is joined by Dr. Wahida Samady, who shares the latest science and global context on food allergies, including the role of the skin, the environment, and dietary habits around the world.

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Key Discussion Points and Insights

1. Food Allergies: The Personal and Scientific Spectrum

• Host’s Experience: Aaron Scott discusses his childhood dairy allergy.
  • "When I was growing up, I was allergic to dairy...my nose would get totally stuffed up." (00:24)
• Severity Can Vary: Dr. Samady outlines the range of food allergy reactions.
  • "There are other people that will describe like a sense of doom almost that kind of comes over them...throat closing...itching and swelling...nausea and vomiting...a whole body takeover." (00:35–01:13)

2. The Food Allergy Epidemic

• Prevalence Has Risen Sharply:
  • "Before the 1990s, the rate...was below 3%...Now, 1 in 13 children have a food allergy." (01:24–01:48)
• Geographical Differences:
  • The rise is concentrated in "America, Western Europe, Australia, and parts of Asia and Africa. But...there are still places...where no one has a food allergy." (01:58)

3. Theories Behind the Increase

• The Mystery:
  • "That is the million dollar question. We have a lot of theories." (02:27)
• Featured Theory:
  • "You absorb the food through your skin before you eat it and then your body decides it is something to attack." (02:40)

4. What Happens During An Allergic Reaction?

• Biological Process (04:13–05:37):
  • Food is broken down in the intestine, then absorbed.
  • Immune cells along the gut label certain foods as threats, releasing chemicals (cytokines).
    • "It’s basically telling your body an invader has come, we have to fight."
  • This triggers inflammatory cascades, leading to swelling, hives, and itching.
  • "One of the products...is histamine. And that's why you get itchy, and that's why you get hives." (05:37)

5. Treating Allergic Reactions

• Mild Reactions:
  • Treated with antihistamines (for itching, hives, rash).
• Severe Reactions:
  • Require epinephrine (adrenaline) via injection.
  • "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." (06:00–07:00)

6. Why Do Some People Develop Food Allergies?

• High-Risk Indicator:
  • Early, severe eczema in children is a strong predictor.
  • "One of the first signs...is that they have eczema. The earlier you develop eczema, and the more severe...the higher the risk." (07:07–07:42)
  • Gut flora differences noted in children with eczema.
• Skin Barrier Hypothesis:
  • Disrupted skin allows food particles in, teaching immune cells to treat foods as threats.
    • "Food can get into a broken skin barrier...they might label those food proteins as something bad." (08:33–09:01)

7. Global Differences in Food Allergies

• Vary by Region and Culture:
  • Different foods are allergenic in different countries (e.g., lentil/chickpea in India, shellfish in East Asia).
    • "Globally, for example, different countries will have different types of allergic foods." (09:10)
  • Processing methods matter:
    • In the U.S., peanuts are mostly roasted, which may enhance allergenicity versus boiling in other regions.
    • "We do think the roasting process itself makes peanuts...more likely to set off an allergy." (10:17)

8. If You Suspect a Food Allergy

• Seek Medical Advice:
  • Avoid unnecessary dietary restrictions—consult professionals for testing and diagnosis.
  • Some symptoms may not be immediate-type allergies, but rather histamine reactions or oral allergy syndrome.
    • "There are so many people that think they have one of these immediate-type reactions and they don't. But they've been avoiding large groups of foods." (10:29–11:51)

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Notable Quotes and Memorable Moments

• "We call it an epidemic because it has risen dramatically over the last few decades."
  – Dr. Wahida Samady (01:24)
• "Some of these symptoms that you're having are just secondary to the inflammation that the body is creating."
  – Dr. Samady (05:10)
• "If you have a disrupted skin barrier and food particles are getting in through the skin...those immune cells...might label those food proteins as something bad."
  – Dr. Samady (07:58–09:01)
• "Different countries will have different types of allergic foods...It's also thoughts about how we process our food."
  – Dr. Samady (09:10–10:17)
• "When you are in a severe reaction, nothing else is really going to take away the reaction or stop it from progressing the way epinephrine would."
  – Dr. Samady (06:54)
• "What I would really recommend...we really should try to find a healthcare provider that can help you get tested."
  – Dr. Samady (10:34–11:51)

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Timestamps for Key Segments

• 00:24: Aaron’s personal food allergy story
• 00:35–01:13: Dr. Samady describes severity of reactions
• 01:24: Food allergy statistics and the "epidemic"
• 01:58: Global prevalence differences
• 02:27: Theories behind the rise in food allergies
• 04:13–05:37: What happens biologically during a reaction
• 06:00–07:00: Treatments for mild vs. severe reactions
• 07:07–07:42: Eczema as risk factor; microbiome differences
• 08:33–09:01: Skin barrier theory
• 09:10–10:17: Regional differences in food allergies, peanut processing
• 10:34–11:51: Advice for those who think they have food allergies

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Episode Takeaways

• Rising Rates: Food allergies have doubled in children since the 1990s, but this rises mainly in Westernized countries.
• Skin Barrier Theory: Disrupted skin in young children may introduce foods as allergens before oral tolerance is established.
• Diagnosis Matters: Many attribute unrelated symptoms to allergies—proper diagnosis is crucial to avoid unnecessary deprivation of important foods.
• Cultural Context: The foods people are allergic to, and the risk of developing allergies, vary around the world due to diet and food preparation methods.

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This engaging episode is accessible for anyone curious about the science behind food allergies, combining personal anecdotes, clear explanations, and the latest hypotheses in allergy research.

Transcript

[A]

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[B]

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.

[C]

There are other people that will describe like a sense of doom almost that kind of comes over them.

[B]

This is Wahida Samdy, the director of clinical research at Northwestern University's center for Food Allergy and Asthma Research.

[C]

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.

[B]

People can be allergic to all sorts of things, from bee stings to medicines. But Waheeda's specialty is food allergies, and their prevalence is exploding.

[C]

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 US amongst everyone was below 3%, maybe 2, 2.5%. And just in children alone. Research studies have found a dramatic increase over that time. Now we look at 1 in 13 children have a food allergy.

[B]

That means allergy rates have basically doubled. But the strange thing is this rise in allergies is not happening equally across the globe.

[C]

The rise has definitely occurred in America, 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 you know, interestingly enough, what people are allergic to is also very different. So that varies globally. Globally as well. But no, food allergies are definitely on the rise in certain countries, but not others.

[B]

And do we know why?

[C]

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.

[B]

So today on the show, we try to answer that million dollar question one theory you 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.

[A]

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[B]

Wahida, 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?

[C]

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 more 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.

[B]

And so what sort of tools do we then have to treat these reactions and what are they doing on a molecular level?

[E]

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, you 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 epinephrine would.

[B]

What do we know about why some people develop these food allergies, while most people do not?

[C]

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 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. 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 testing if you eat peanut butter in the house, do you have peanut in the dust in your house?

[E]

Yes, you do.

[C]

There's peanut particles everywhere. And so definitely food can get into a broken skin barrier. And when it does, 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, they're 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.

[B]

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.

[C]

So we know that within the United States, for example, food allergies will differ for different races and 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 does definitely does vary. There's also thoughts about how we process our food. So, you know, the big question is, like, why? Why peanut?

[B]

Right. Because peanuts are a leading allergen.

[C]

Yeah. And it's a hard one to know. 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 peanuts are boiled.

[E]

Here they are roasted.

[C]

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.

[B]

So if someone thinks they have an issue with a food, what should they do? Where do they start?

[C]

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 large groups of foods. 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, I say this with some sensitivity, but we really should try to find a healthcare 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 about your day and also understand what kind of allergy you do have and what to do about it.

[B]

Well, Waheeda Samity, it's been a joy talking with you. Thank you for taking time today.

[C]

Thank you, Erin. Thank you for your interest.

[B]

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 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.npr.org 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.

[C]

Foreign.

[D]

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