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Rad Scientist Ep. 8: Body Odor, It's Not The Pits

Chris Callewaert is pictured in this undated photo.
Jelle Vermeersch
Chris Callewaert is pictured in this undated photo.
Ep. 8: Body Odor, It’s Not the Pits
Why do armpits smell? And how can we make them smell better? Chris Callewaert, also known as "Dr. Armpit," thinks he's solved this vapor caper. This is a KPBS Explore podcast. Find more KPBS podcasts at Subscribe to the Rad Scientist podcast on iTunes, Google Play or your favorite podcatcher.

Margot: Why do you think armpits get such a bad rap? Chris: Because often they smell. [Quirky Music Starts] Chris: There are some armpits that smell, like, garbagy, very sour, strong ammoniac, sulfurous, oniony, and fecal-like. If that would be my superpower I would solve their body odor. People call me Dr. Armpit. In the beginning to mock me a little bit but I soon embraced it and I quite like the name. The name says it all. Margot: This is Rad Scientist. Where the scientist becomes the subject. Dr. Armpit, also known as Chris Callewaert, is a joint postdoctoral fellow at UCSD and at Ghent University in Belgium. As you may have guessed he studies armpit odor. And get this, I meet him at his lab – located in a building called Chris: Barf 2 – this is the biomedical research facility II. Margot: Dr. Armpit works in Barf II. All is right in the world. Now, Chris didn’t grow up knowing that he wanted to study body odor. In fact he didn’t get stinky until he got older. Chris: I did not have any body odor whatsoever until the age of 21. Then, to make a long story short, I met this girl. I spent the night in bed with that girl. And, the day after, my body odor completely changed. Margot: And not in a good way. Chris was perplexed. How could his smell change so quickly? Chris: Quite awkward and strange. I was like what the [BLEEP] is that. So I started investigating the problem. Margot: He gets a little obsessed, reading all he can about it. During his literature binge, he comes up with an idea for how to get rid of body odor. He wants to test his idea scientifically, in graduate school at the Ghent University. Chris: I pitch the idea to several professors at the university and they like it. Margot: He applies for a fellowship to do his PhD on armpit odor and he gets it. Chris: And the rest is history. … Margot: So what did Chris find when he was researching his new BO problem? And what is his idea to solve it? Well, first we have to start with some basics. Like what is body odor- and who, or what, is to blame? Chris: We basically are covered in sweat glands. Most of them are eccrine sweat glands, just secreting water and salts. But in your armpits you also have apocrine sweat glands. It is only developed with puberty. Margot: These apocrine glands secrete more than just water and salts. They secrete Chris: “lipids, fatty acids, amino acids” Margot: Now don’t worry. These aren’t the smelly culprits. However, they are a very enticing meal for some microorganisms. Think about it- armpits are like a warm chalet with an all you can eat fondue bar. Chris: It’s very warm, it’s very moist, and there is a lot of food present there. Margot: So who comes to stay at chalet armpit[French accent]? Bacteria – a lot of them! Chris: You can have more bacteria on your armpits than there are humans on this planet. Margot: Billions of bacteria. [play sound of bustling restaurant] They are munching on your armpit food. When they are done they leave behind scraps, byproducts – and those are the things that smell. [fade music down] When Chris told me this, it turned a lot of the assumptions I had about body odor on their head. I thought that body odor was 100% genetic- like once a person with BO always a person with BO. Chris: You know, you’re not born with it. It’s generally the microbiome that is present there and converts molecules into malodorous molecules. Margot: Of course that is not to say that there are NO genetic impacts to body odor. Changes to the output of your apocrine glands can change how many and which kinds of bacteria will come to eat. Chris: For instance, if you go to Japan or South Korea, they barely have any body odor and that’s because they have a deficiency of a certain enzyme, of a certain gene. Margot: This gene helps you make the armpit food. Without it… Chris: You will have much less apocrine sweat, and the ones that you secrete will not be easily converted by bacteria. Margot: There are many types of bacteria that can munch on your goods. Some of them leave odorless molecules behind, and others leave smelly stuff behind. And that takes us back to Chris’s one night stand and how he magically acquires body odor after a night of romance. His theory? Chris: That I picked up some sort of microbiome that wasn’t mine that was now causing some body odor. Margot: He thinks that he picked up bacteria from the girl he spent the night with. And this idea changes the trajectory of his life. Because now he can’t stop thinking about this potential microbiome swap. He figures that the reverse of what happened to him should also be possible. Like what if a person with bad body odor was given good bacteria. Would their BO go away? That’s the idea that landed him in graduate school. To find out how Chris tests this idea, stick around after the break. … Chris had an idea about why he suddenly had bad body odor- that bacteria were to blame. Now he sets out to test his theory. Margot: Step one for Chris is to figure out which bacteria are the good guys and which are the bad guys- which are correlated with less pleasant smells and which are correlated with more pleasant smells. Here’s how he got to the bottom of this vapor caper. First he needed to sample some armpits and catalogue how they smell. Chris: So we work with a human odor panel and that’s four males, four females which are selected, trained to do this kind of work. Margot: If you are imagining lab coat donning people lining up to stick their nose into a subject’s armpit, than you are kinda right. Chris: We did that in the beginning. That is actually the old fashioned way of doing that. Margot: Chris worried that this method might introduce unnecessary bias. Chris: Because if you see the person you might rate it more good or bad based on how you perceive that person. Margot: To make it more objective, he wiped armpits with cotton pads and put those pads in a jar for sniffing. Chris: And then we rate on hedonic value that is the pleasantness of the odor going from very bad, minus 8, to zero, neutral, to plus 8 which is basically perfume. Margot: No armpits come away with a score of 8, but believe it or not, Chris says some armpit odors are rated with positive values: ones, twos or threes. Anyways the armpits are scored for smelliness - Now, Chris needs to figure out which bacteria are hanging out in those armpits. He does this with a quick swab and some DNA sequencing. It turns out that one bacteria was correlated with pleasant or non-offensive odors. It’s called Staphylococcus epidermis. Chris: And that’s the good one. Margot: A different bacteria was most often found in armpits that did not smell so good. Chris: Corynebacteria. Yea that’s the guys you don’t want. Margot: Ok so we have our good guys we have our bad guys. What’s next? It’s not enough to know the likely culprit of armpit BO – Chris wants to solve it! His idea? Get rid of the bad bacteria and replace it with the good one . Take the bacteria from a good smelling armpit and try to transplant it onto a bad smelling armpit. His first guinea pigs were a set of identical twins that weren’t completely identical. Chris: You can barely distinguish them based on sight, but based on odor, you can definitely distinguish them. Margot: Chris asked Twin A with the nice smelling armpits to stop showering for four days. Twin B was instructed to wash thoroughly with antibacterial soap. Then he took sweat from twin A, wiped it on twin B and voila Chris: That immediately solved the situation. Margot: With one success under his belt, he starts testing more pairs of people – not identical twins, but family members. He thought that would make it less awkward and make it more likely that the good bacteria would take to its new home. That trial was pretty successful. After one month, most of the transplanted armpits were smelling kind of nice. But when Chris checked in three months later..about half of the participants had smelly armpits again. Their original armpit microbiome had reclaimed their territory. Chris: It can be in your old clothes; it can be in your washing machine. So yea, it’s difficult. It’s possible to change a microbiome but it’s also possible that it goes back again. Margot: No matter the cause of the reversion, Chris is not satisfied with the armpit transplant method. He thinks there might be a better way, a better spray. What if one could directly apply the good bacteria and do that consistently. Probiotics for the armpit. He’s starting a clinical trial in Belgium to test his idea. If it works, he’ll try to start a company to get his spray on the market. Chris is really driven to find a solution because he knows that for some people, body odor can have profound effects on self-esteem and lifestyle. He interacts with people with issues around body odor online through a forum he created. Some users ask questions like why does my right armpit smell more than my left? Others request to be a participant of his next study. Some share tips that have worked for them. And some just go to share their experience just thankful to find that they aren’t alone in feeling discomfort or shame about their odor. Chris remembers a guy in his late forties that came to participate in one of his transplant studies. Chris: He came to us and he said look I’ve been suffering from body odor my whole life. I chose to be self-employed to be far away from everybody else. And I said, do you smell it yourself? He said no because I’m working a lot on dust and it’s obstructing my nose so I don’t smell it myself. And I said why do you think that you smell bad? And he was like, well people say that to me when I was 16 years old – a couple of bullies kept on saying that. And then we did the analysis. So eight people really smelled it. And the conclusion was that he doesn’t smell. Margot: It’s really tragic when you think about it. Chris: He believed his whole life that he smells bad because of a couple of bullies that said that to him. He chose his job based on that. Basically his whole like was determined by it and then it appears that he doesn’t have body odor. Margot: Can you imagine how that must have felt, to be told that, in fact, the thing that held you back for so long just wasn’t true? Chris: And then he was like, “I cannot thank you enough. I was waiting for this my whole life.” Margot: This guy is not alone. Chris says that people tend to think their body odor is much worse than others perceive it to be. For one- you are a lot closer to your armpits than others get. But also, like many things about ourselves, about our bodies, we are our harshest critics. Perhaps it helps to know that we aren’t the culprit of our armpit odor? That it is bacteria that is to blame. And bacteria, our microbiome, is an important part of us functioning as human beings. Chris: Bacteria are everywhere. You can’t avoid them so you better embrace them. Margot: But we can choose the ones that make us feel better- make us more comfortable. And maybe, in the future, we will be better at controlling our bacterial ecosystems the way we do with our yards. Culling the weeds, and planting roses. That’s the future that Chris envisions. But back to Chris, what ever happened to his body odor? Chris: Somewhere in the middle of my PhD, sort of by accident, I was painting my house and I sort of had this painters t-shirt over and over again without washing it. I took a shower, but the t-shirt didn’t take a shower. Margot: He starts noticing that his body odor is getting much better. Chris: I knew that something had changed over the summer. That I no longer had to take a shower. Margot: He has a theory for what happened based on his research. He’s done work suggesting that cotton grows bacteria very well, and mostly the good kind. This t-shirt had his old microbiome on it. Chris: That’s basically how I transplanted my own bacteria onto myself. Margot: So while Chris’s BO may be gone for now, he knows that for many, their BO will persist. He’ll continue his mission to find a way for everyone to be BO free. For this week’s Moment of Xenopus: A Superhero trailer for Dr. Armpit. Narrator: In a world, where body odor is ruining lives. Chris: Chorynobacteria, yea that’s the guys you don’t want. Narrator: There is only man who can save us Chris: I’m just a regular guy. Narrator: When one night he realizes, he might have what it takes to get rid of the bad guys Chris: That would be my super power. Narrator: So he puts on a white lab coat. Chris: People call me Dr. Armpit. [laughs] Narrator: Dr. Armpit, coming to theatres in the near future. Margot: Rad scientist is produced by me, Margot Wohl. This episode was written by myself with edits by Jill Jainero and folks at ComSciCon national which is a free workshop for graduate students to hone their science communication skills. Applications are open now for ComSciCon 2019 which will be held in San Diego. Our theme guitar riff is by Grant Fisher. Logo by Kyle Fischer, no relation. Music for this episode was by Cullah, Julien matthey, podington bear, and kinoton. At KPBS, Emily Jankowski is technical director, Melanie Drogseth is program coordinator, Jill Linder is programming manager, Kinsee Morlan is Podcast Coordinator, Lisa Jane Morrisette is Operations Manager, and John Decker is director of programming. This program is made possible in part by the KPBS Explore local content fund. If you liked this episode, tell a friend or rate and review us on itunes. It really helps.

When Chris Callewaert suddenly got body odor years after puberty had hit, he wondered how he could have suddenly become smelly. It timed out pretty well with a one night stand he had with a woman who had a similar smell to what he was noticing in his armpit.

He put two and two together, and came up with a hypothesis that the woman had transferred some new bacteria to his armpits. That's when he decided that he wanted to go from "Mr. Callewaert" to "Dr. Armpit" by studying the microbiome of armpits at Ghent University in Belgium.

Now a joint postdoctoral researcher at Ghent University and UC San Diego, Callewaert's testing out new theories for how to get rid of body odor for good.


To stay up to date with Chris' research or to chat on his forum, go to You can also follow him on Twitter at @DrArmpit.