Allergic To Cats? There's Hope Yet! : Short Wave Katie Wu is a cat person. She has two of them: twin boys named Calvin and Hobbes. But up until grad school, she couldn't be anywhere close to a cat without her throat tightening and her nose clogging up. In a stroke of luck, Katie's cat allergy suddenly disappeared. The reasons for her night-and-day immune overhaul remain a mystery.

In this episode, Katie walks host Aaron Scott through the dynamic world of allergies and what it reveals about our immune systems. Calvin and Hobbes make cameo appearances.

Allergic To Cats? There's Hope Yet!

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EMILY KWONG, BYLINE: You're listening to SHORT WAVE from NPR.

KATIE WU: The nervous one is close by. But - one sec. Hi, buddy.

(SOUNDBITE OF CAT MEOWING)

WU: Oh, can you meow again?

AARON SCOTT, HOST:

Katie Wu is a cat person. She has twin tabby brothers, Calvin and Hobbes. The meowing you heard came from Hobbes.

WU: Hobbes is a Zoom enthusiast, but a nothing else enthusiast. He is afraid of food, human beings, other cats, heavy steps, vacuum cleaners, wind and foil. He likes having his teeth rubbed. So I'm doing that to calm him down.

SCOTT: Katie loves her boys, but she wasn't always a feline mother of two. In fact, this wasn't a situation she ever saw herself in at all.

WU: If we put me 10 years ago into this exact room, it would be a catastrophe.

SCOTT: Tell us about it. What would happen? Oh, I missed that pun.

(LAUGHTER)

WU: OK.

SCOTT: OK. OK.

WU: Yeah. So basically, for the first, I'd say, 20 years of my life, I was - I wouldn't say deathly allergic to cats, but whatever is one tier below deathly allergic to cats.

SCOTT: Miserably.

WU: I'd walk into a room either where there were cats or where cats had recently been or - as distantly as months ago - and my body could tell. My eyes would start watering. My nose would immediately clog up. I would feel my throat tighten.

SCOTT: It's possible for Katie, it was genetic.

WU: It happened to my mom, too. My siblings have it. It's - like, this was my destiny.

SCOTT: Or so she thought. Because sometime between the end of college and grad school...

WU: I was suddenly able to be around cats and nothing would happen.

SCOTT: Katie remembers that around this time she even went with a friend to help them adopt a dog. They hung out in the shelter for hours. There were rows and rows of cats in a facility full of dander and cat hair and other cat remnants. And she was completely fine.

WU: I did not know what was going on. So after that, I sort of decided to test it out more and more and more. And just - it kept being the case that nothing would happen.

SCOTT: People can outgrow allergies, but it seems less common to have the kind of complete night-and-day change that Katie experienced.

WU: So either this is the longest fever dream ever or something in my body changed that just decided, you know, one day your immune system is terrified of cats, and then it got over it.

SCOTT: So today on the show, we talk to Katie Wu about the complex world of allergies, why they may happen and what might cause them to change, turning even the most cat-allergic into the cat-obsessed.

WU: Do you want to meow? Can you meow, and can I record it?

(SOUNDBITE OF CAT MEOWING)

SCOTT: I'm Aaron Scott, brand-new dog owner of Oliver Seraph Scott-Lamb (ph), and you're listening to SHORT WAVE, the daily science podcast from NPR.

(SOUNDBITE OF MUSIC)

SCOTT: We at SHORT WAVE love pets - feline and otherwise. We love snuggling them, and we love producing stories about them. And if you want to help us create more animal kingdom content, then sign up for NPR Plus. It means you get the show ad-free, and you're contributing to our ability to unlock feline mysteries. If you're already a subscriber, thank you, thank you, thank you. Find out more at plus.npr.org/shortwave.

(SOUNDBITE OF MUSIC)

SCOTT: So, Katie, let's dive into the biology of allergies. You write that they're basically like little molecular screw-ups. What do you mean by that?

WU: Yeah. So, I mean, think about the things that people tend to be allergic to - peanuts, pollen, shellfish. For most people, these are harmless things, and they should be harmless things. But the sort of classic version of this is you're exposed to something a couple times, usually early in life - there are some exceptions to that. You know, maybe the first time, the body sees it and goes, huh, something about this doesn't sit right with me. Some sort of response develops, and the next time that same allergen comes around, the body's like, oh, no. The last time I saw this, I got really nervous, and now I am giving, like, a full-blown freak-out.

SCOTT: Katie says there are basically two parts to an allergic reaction.

(SOUNDBITE OF MUSIC)

WU: Step one is your body has to first recognize the thing as something that just raises its hackles.

SCOTT: It's called sensitization. Something triggers a hypersensitivity in the immune system. And then...

WU: Those crazy symptoms are the actual allergic response. So it's like detection, reaction. So when people's bodies overreact to them - you know, when they get hives or they go into anaphylactic shock, they stop being able to breathe, like, some people can even die from these reactions - these are basically overblown reactions to something that really should be harmless.

SCOTT: And from what you write that really surprised me is it's not just one biological process. It's complicated. It's particular to the allergen. It differs from person to person. Tell us a little bit about what we're learning about how complex it is.

WU: It's not like you can simply look at someone or even look at their reaction to an allergen and say, oh, I know exactly what's happening molecularly in your body, which makes it really difficult to say, I have a good plan for treating you or making these symptoms better. You know, the general way that people approach this, and the most common way that people approached this for a long time, was to give people antihistamines, which is basically treating a symptom of the allergy, but it's not really tackling it at the source. It's not teaching the body, hey, chill out. This thing that you're scared of is actually benign. It's really just saying, let's make you feel better after your body starts reacting.

And so, you know, a lot of this is, like, happening kind of downstream of the big problem itself because that can happen in so many ways. And it's also not like allergies can manifest in the same way. Like, think of anyone you know who has seasonal allergies - hay fever. They sneeze a ton when they have pollen. And then compare that to someone who is allergic to peanuts and is going into anaphylactic shock in a restaurant. Those things look so different.

SCOTT: You write that the world is becoming a more allergic place, that in America alone, there's about 50 million people who experience allergies. Do scientists have a sense of why this is?

WU: I think we have become a very super-clean society, especially in the Western world. And kind of ironically, like, you would think that leads to people getting less sick. But that also means we're not exposing kids to a lot of the really good microbes that are helping train little kids' bodies to distinguish good from bad. And so as dietary practices have changed, as we're, you know, using tons and tons of antibiotics, there are some thoughts about, you know, how the differences of modern childhood are making it easier for bodies to basically get confused about what does and doesn't belong inside of them.

SCOTT: And do you have any sense of how much it's an actual rise in allergies versus an artifact of, you know, people are looking for them more and that it's more a rise in reporting or a diagnosis?

WU: Yeah, that's a fantastic question. And, you know, to be totally honest, there is a little bit of both going on. But even studies that have sort of tried to account for the rise in diagnosis and awareness and just of parents coming in and being very worried about this specific thing, there does seem to be a rise in this. I think any allergist you talk to you - you'll ask them, is - are kids more allergic than they were a few decades ago? And generally, the answer I've gotten is, oh, yeah. It's definitely a thing. But that said, there is definitely an overdiagnosis problem with some allergies. Penicillin is an amazing example. Apparently 90% of people who have penicillin allergy in their medical chart don't actually have a penicillin allergy. And this is a huge problem with drug allergies, not just 'cause there's erroneous information in those drug charts, but because it limits the options that people can get when they get a bacterial infection.

SCOTT: Katie, what are the ramifications for public health of having this increasingly allergic planet?

WU: This is absolutely, I think, becoming a bigger issue. Because even above and beyond the fact that allergies can be a debilitating thing to live with and it is costing a lot of money and resources to figure out how to improve these people's quality of life and find adequate treatments for them and to just better understand this growing phenomenon, I think it is indicative that we don't fully understand just fundamental aspects of the immune system. If allergies are increasing, I think that sort of also speaks to, are we putting our kids in the best environment? Should we be taking a closer look at childhood? Should we be taking a closer look at built environments? Should we be taking a closer look at, say, our early relationships with animals or other humans? And, like, if there are race or socioeconomic disparities, why might those be? So it's kind of both, like, an effect and a symptom of a bigger problem that is definitely worth examining.

SCOTT: Katie's one of the lucky anomalies who managed to kick her cat allergy. But allergies change in people all the time. They wax and they wane. And while researchers don't always know what determines all of these immune changes, there are some scientific explanations.

WU: Basically, this is called tolerance. After you develop an allergy, you can lose it by growing tolerant to the antigen. Your body learns over time, almost like the immune system version of exposure therapy. And this is the principle behind allergy shots, right? But it's complicated. They don't always work because people's immune systems are very weird. And sometimes people just grow out of their allergies without a super clear explanation. I had no obvious intervention. So I am just sort of chalking it up to the weirdness of immune systems being sort of sensitive to all sorts of change over time - like how we're sleeping, how we're eating, what's inside of our guts bacteria-wise, where we live, how old we are. Maybe just the right combination of factors happened for me at the right time.

SCOTT: The hope is, as scientists further unlock the mysteries of allergies and our immune systems, they'll have more tools to go about treating them.

WU: I think there are definitely people who are talking about, like, gene therapy. And then, of course, there are people who are trying to figure out, how can we tackle this, not on the human side, but on the side of the allergen? You know, obviously, there have been a lot more accommodations as of late to make foods more allergy-friendly for kids. And then there are ideas about how to prevent allergies from manifesting in the first place. So changing the habits around what, you know, pregnant people are told to eat, what lactating people are told to eat - just making sure those exposures are happening early. You know, there are some people looking into whether it's actually really beneficial to have a pet in your home when you have a really little kid - you know, to obviously not overuse antibiotics. But I think a lot of things both on the treatment side and the prevention side.

SCOTT: Katie Wu, it's been a pleasure talking allergies with you. Thank you so much for bringing Calvin and Hobbes into our world.

WU: Delighted to be here, as always. I am a cat fan, so any time you want me back, just say the word cat.

(SOUNDBITE OF MUSIC)

SCOTT: SHORT WAVE depends a lot on our pets - a lot, a lot, a lot. And, yes, most of the team are cat people, to be honest, although I will voice my doggie dissent here. So to contribute to the ca-cat-phony (ph) of noise that little Hobbes made earlier, I bring you...

KWONG: Zuko.

(SOUNDBITE OF CAT MEOWING)

SCOTT: Zuko, the fiery red tabby and owner of SHORT WAVE co-host Emily Kwong.

KWONG: Do you like the microphone?

(SOUNDBITE OF CAT MEOWING)

SCOTT: Kiki, editor Gabriel Spitzer's feline companion.

(SOUNDBITE OF CAT MEOWING)

SCOTT: Baby, owner of producer Margaret Cirino.

(SOUNDBITE OF CAT MEOWING)

SCOTT: And lastly...

(SOUNDBITE OF CAT MEOWING)

SCOTT: The cat who runs the whole show and also our senior supervising editor, Gisele Grayson, Pele (ph).

(SOUNDBITE OF CAT MEOWING)

SCOTT: This episode was produced by Abe Levine, and Margaret and Baby. It was edited by Gisele and Pele. Brit Hanson checked the facts. The audio engineer was Stu Rushfield. Brendan Crump is our podcast coordinator. Our senior director of programming is Beth Donovan, and the senior vice president of programming is Anya Grundmann. I'm Aaron Scott. Thanks, as always, for listening to SHORT WAVE from NPR.

(SOUNDBITE OF MUSIC)

SCOTT: Calvin and Hobbes are both big fellows.

WU: You want to say hi? Say hi. Speak. You're so rude. You never do anything I tell you.

(SOUNDBITE OF MUSIC)

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