The Hygiene Hypothesis Explained: How Dirt, Pacifiers & Dishwashers Affect Allergies | Allergy Actually

The Hygiene Hypothesis: Could Being "Too Clean" Cause Allergies?

Could hand sanitizer, spotless homes, and a fear of germs actually be contributing to the rise in allergies, asthma, and eczema? It's a fascinating and counterintuitive idea known as the Hygiene Hypothesis.

In this episode of Allergy Actually, your bestie allergist moms – Dr. Kara Wada, Dr. Amber Patterson, and Dr. Meagan Shepherd – dive deep into the science of "a little dirt." They explore how early life exposure to a diverse range of microbes "trains" our immune system to be less reactive.

Learn about the compelling research comparing Amish communities to modern Western societies, the crucial role of the skin barrier in preventing food allergies, and why the advice to delay introducing allergenic foods was a major misstep. This episode will change the way you think about germs, dirt, and raising healthy, resilient kids.

EPISODE IN A GLANCE
00:28 What is the Hygiene Hypothesis?
02:50 Amish Communities & The "Cleanliness" Link to Allergies
05:01 Practical Parenting: Dishwashers, Pacifiers & Preventing Atopy
06:50 The Skin Barrier's Role in Developing Food Allergies
10:11 How the LEAP Study Revolutionized Food Introduction

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ABOUT HOSTS
KARA WADA, MD
Dr. Kara Wada is a quadruple board-certified physician in allergy, immunology, and lifestyle medicine, and founder of the Immune Confident Institute. As a Sjogren’s patient and life coach, she combines modern medicine with lifestyle and mindset practices to help patients harness their body's ability to heal.
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AMBER PATTERSON, MD
Dr. Amber Patterson is a world-renowned allergy and immunology expert pioneering the future of immunotherapy. As the U.S. ambassador for ILIT™ Protocol (a 3-injection allergy shot protocol), she is redefining allergy care through her practice, Auni Allergy®, and the groundbreaking Auni® ILIT™ Learning Network.
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MEAGAN SHEPHERD, MD
Dr. Meagan Shepherd is a board-certified allergist and immunologist with nearly 15 years of experience specializing in advanced immunotherapy. She is known for her practical, evidence-based approach and her unique focus on "allergy-conscious living"—designing homes, habits, and lifestyles that improve her patients' quality of life.

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Transcript

Amber: Could hand sanitizer and spotless homes be part of what's making us sicker? Let's get into it. Today we're diving into the hygiene hypothesis, why a little dirt might actually do your immune system some good. We are your board-certified allergist besties.

What is the Hygiene Hypothesis?

Amber: So ladies, this is something that I feel like we've been talking about in the allergy world for a long time, like since all of us started training moons ago. But it's still one of those things if, you know, if I'm in a party, a lot of allergy topics are popular for cocktail party chatter. And if this ever comes up, people are just like, Whoa. Tell me more about the hygiene hypothesis and what this means for allergies and

So I guess just to give a little brief summary of what we mean by the hygiene hypothesis. Allergies have been on the rise, atopy in general, which is a term for all the different kinds of allergic disorders, food allergy, asthma, eczema. And over the years, there's been multiple studies coming in about different aspects related to the hygiene of our culture and how that may be related to kind of in the end, this increased rise in atopy.

Because when we learn about the microbiome and all of the organisms that are not only on our bodies, in our bodies, around our bodies, on other organisms around us but we're learning that those interactions have a big role in how our immune systems develop. It's kind of a use it or lose it. You know, if we have lots of exposure, our immune system gets lots of practice with how to have polite conversations with other, you know, organisms in the world around us. Versus if you never see this diverse array of organisms, how your immune system learns to respond in that environment. So, do you guys wanna give some maybe more detailed examples of parts of this hypothesis?

Kara: One of the things that I always found so fascinating in general, just because I honestly wonder if I should have been like a sociology major, like if I, if I would've known what that all entailed or anthropology, maybe anthropology is actually a better a better description of what I'm thinking about. But all of the research that looks at folks from our Amish communities and their lower rates of allergy, asthma, all these different atopic diseases. So we, we've kind of known about that in the US.

There's also some really fascinating data that comes from Finland and Russia, the border there, where geographically they're like right next to one another.

But for, you know, many decades Finland was considered kind of western and and Russia at that point in time was the USSR. So, you know, very different kind of exposures and lifestyle that those kids were growing up with. And there are in those cultures too, you see a difference in the rates of allergies, asthma, and also autoimmune diseases too.

Amber: And which cultures are the ones that have higher rates of allergy versus lower?

Kara: Yeah. Finland and then those of us that are not living the Amish ways.

Amber: Yeah, so the ones who are, we'll call it like in cleaner environments, you know, we give

Kara: for lack of a better,

Amber: birth in hospitals and sterile environments. 

Amish Communities & The 'Cleanliness' Link to Allergies

Amber: We, you know, have very clean homes. Most of our soaps that we buy at the store for washing our hands just have antibiotics in them, whether we want it or not, just part of what's in there.

We use dish washing machines to heat our forks and spoons and plates to a really high temperature to kill everything in the washing machine. So yeah, those developed countries where we have less exposure to dirt, other organisms, higher rates of allergy.

Meagan: When I had my kids, I look back, so my oldest is almost 15, and that was before I was a resident, a Med-Peds resident, and I had not done an allergy fellowship, and I really didn't think about the development of allergy at all. And, in, in retrospect, the things we were doing at the time were actually helpful, but I didn't realize it.

When the twins came along, I was already a practicing allergist out on my own in an academic setting, and I really thought so much about that for them. And I was surprised. We don't really have a family history of atopy, but it was really on my mind and so I made a decision that I was gonna do everything I could to get them to not be atopic.

Practical Parenting: Dishwashers, Pacifiers & Preventing Atopy

Meagan: And so one of the things I did was for their bottles, I would not wash them in the dishwasher, I would hand wash them and then let them air dry. Which there are studies, you know, there's at least one study that supports using a dishwasher versus handwashing bottles that, that lead to increased rates of atopy if you are using a dishwasher.

Amber: Yep.

Meagan: One of the other things, they were premature well they were late preterm. So my my husband was like, we're absolutely not doing this. But I recall there was a study that said that when they dropped their pacifier, children whose parents cleaned them by like putting it in their mouth instead of washing it with soap and water actually had lower rate, I think it was lower rates of atopy and I was like, we're gonna do that. He's like, we are not.

Amber: That's so interesting because there's a study of thumb sucking Amish and similar concept, like the more introduction to a diverse organism is good for our immune systems.

Kara: Yeah.

Meagan: It's fascinating. And

The Skin Barrier's Role in Developing Food Allergies

Meagan: one of the things that when we were chatting about this earlier that was brought up was the question about whether or not barrier plays a role. We just used to think of it as the hygiene hypothesis only, but now we know that some of the issues with allergy also seem to arise from where your first exposure occurs to certain things.

So, in our world there are so many products out there that are using food stuff in some way. And so we sometimes think or, or there's some evidence to suggest that if your first introduction to something is via the skin, which is not really where that's supposed to happen, it's supposed to be happening in your gut, that that's where the immune reaction kind of goes haywire and leads toward an allergic type of reaction.

And I was a big believer in that. I remember my husband used to eat mixed nuts all the time. And one day one of the twins was crying and they were like six months old and he went over and picked one up and I was like, "Stick your finger in his mouth. Stick your finger in his mouth!" And he's like, what? He looks at me like I'm crazy. And he like slowly, like he pauses and he's like, okay. And he like slowly sticks his.

Amber: Oh my gosh, that's really funny.

Meagan: Yeah, "Stick your finger in his mouth. Stick your finger in his mouth." And so he just went with it. He was just like, clearly this is not, I'm not gonna interrupt her. We're just gonna do it and go on. I did not want the first introduction to tree nuts to be through the skin. And I thought, well if it has to be through the skin, 'cause they've already picked up, we can at least rub it around the mouth.

Kara: Yeah, I think my, my perception like through parenting kind of evolved and changed with each kiddo. So I had Charlotte, who is about nine and a half while I was a fellow, and she was born right after the LEAP study came out. And so I remember the follow-up study to LEAP was released when she was about four to six months old.

I remember going to that meeting. It was the, the economy meeting in Los Angeles. So we brought her along, my in-laws are out there. And I remember just thinking, gosh, we gotta start all the foods. Like as soon as we got home, I'm like, developmentally she was kind and just getting there, but really trying to be proactive.

And then when we had Josie I was a second year attending and you know, trying to do the same thing. Now, she did have some very mild eczema but she is my kiddo who ended up reacting to scrambled eggs. And so then it was like, "Okay, when she's been eating peanut, but are we okay to keep, you know, peanut in the diet and oh gosh," you know, kind of down that rabbit hole of, of experience. And then, Ollie, he's like the third kid and you know, kind of all along for everything. But you know, I think his sisters were kind of shoving food in his mouth from the get go.

Amber: Yeah. Well, so it's interesting you mentioned the LEAP study. For people who don't know what that is, it, it was a study that came out, was it 2015 or around there, that, that taught us a lot about how and when food allergies develop and how introducing foods earlier, like four to six months could potentially prevent development of food allergy in people who are predisposed.

But when you think about how we as a society in the United States at least, was counseling parents on how to introduce foods. There, there had been a, a that was, that was a big shift at that point, but there had been a big shift maybe like 15 years prior. Because what was happening was there was about a 50 year period where allergies were just skyrocketing and nobody knew why.

And so the early two thousands pediatricians started advising parents, Okay we're not gonna do any dairy until 12 months. We're not gonna do, was it eggs at two years? I'm kind of reaching now and then no nuts.

Kara:  It was like 1, 2, 3, 

How the LEAP Study Revolutionized Food Introduction

Amber: Yep. So next two, three. And so when I was a pediatric resident, I mean, we were talking about this at every well check for babies. It was, you know, oh, don't let grandma give the kid this when you're gone. You know, like, make sure every, all the caregivers know to keep these foods out of the diet. Well, we should've known the grandmas were right, because what the LEAP study showed us was that feeding some of these kids, you know, like in particular, peanut and egg in that four to six month window was actually a great time to introduce it to the immune system and prevent the allergy altogether. So totally shifted our mindset about preventing the allergy.

Meagan: Mm-hmm.

Kara: And I, you know, I think there's this ongoing emergence of evidence that if we can do our best to keep those barriers intact, so to help keep that eczema under control to reinforce, you know, healthy microbiome, whatever that means. You know, we're still trying to understand what that all means, but that those things may help counteract or build some resiliency in the system so that we're not, our, our immune systems aren't glitching or misbehaving.

Amber: Mm-hmm. So as the next generation would say, go out there, touch some grass. We would probably say go touch dirt, but

Meagan: Yeah.

Amber: grass.

Kara: Is that a generation alpha thing that I don't know yet?

Amber: Yep.

Kara: Cool.

Amber: Thank you guys for being with us today. Please comment, subscribe, share. Let us know what else you wanna hear about and tune in next time for 

Meagan: Allergy, Actually.