You may have noticed some strong smells coming from your feet, your friend's breath, or your brother's armpit. Where do these body odors come from?
We'll meet the microscopic organisms responsible and visit the kingdom of Footsteros. We'll also find out why we might find these naturally occurring smells so disgusting.
Plus: A brand new Moment of Um answers the question: Why do stink bugs stink?
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LILIA: You're listening to Brains On where we're serious about being curious.
DUMINKA: Brains On is supported in part by a grant from the National Science Foundation.
VENDOR: Hi, welcome to Stink. We put the fun back in foot funk. Seriously, though, let me know if you want to try on any shoes. I personally recommend our new line of athletic stinkers. The smells are on-point.
MARC SANCHEZ: OK, thanks.
SANDEN TOTTEN: Oh. Hey, Marc. I didn't know you liked stinks too.
MARC SANCHEZ: Yeah, well, I somehow outgrew my shoes. The only ones I can wear are these neoprene booties from my wetsuit.
SANDEN TOTTEN: Me, too. I can only fit my feet in these wooden clogs right now.
MARC SANCHEZ: Do you think it was the experiments we were doing in the lab? Maybe it was when we were trying to grow a tomato that tastes like a pear.
SANDEN TOTTEN: It could have also been those tests we were doing to try to make our toes as sticky as gecko toes.
MARC SANCHEZ: Oh, yeah. That was fun. I hope my feet get back to normal. But I guess the upside is checking out some new foot smells.
VENDOR: Here at Stink, our motto is if you want to perform like the greats, having feet that smell like theirs is the first step.
MARC SANCHEZ: I'm thinking to try in the Serena Williams. Maybe I should go with a Venus. I don't know.
SANDEN TOTTEN: And the historical line is pretty cool, too. I wonder how they figured out what Gandhi's feet smelled like.
VENDOR: Oh, we actually have the world's leading stink scientists. And they've developed a cutting edge technique for recreating the foot scent of just about anybody. There's even talk of them winning a Nose Bell Prize. Am I right? Ready to try something on?
MARC SANCHEZ: I'd love to smell the Serena's please.
SANDEN TOTTEN: And I'll give the Lin-Manuel Miranda's a shot. Thank you.
VENDOR: Here we are. Great choices. So earthy. Can you get that the nose, that really great finish. These are, in fact, two of my personal favorite foot smells.
[SNIFFS]
Wow.
MARC SANCHEZ: With these shoes, I might have a couple of Broadway musicals in me.
SANDEN TOTTEN: Yeah, I may never be able to play Wimbledon, but I smell like I could--
MARC SANCHEZ: Hey, Molly. What's up?
MOLLY BLOOM: Oh, I'm here with Lilia.
LILIA: Marc, urgent news. Do you know that elixir you made to keep tacos upright at all times?
MARC SANCHEZ: Yeah, taco stand cement.
LILIA: We've been testing it, and it turns out it makes your feet grow.
MARC SANCHEZ: Oh, man. That's what it was.
LILIA: But luckily, it wears off after 71 hours and 37 and 1/2 minutes.
MARC SANCHEZ: That's great because we did those experiments 24, 48, exactly 71 hours and 36 minutes ago.
SANDEN TOTTEN: Bummer. I guess our feet will be back to normal soon and we won't need new shoes after all.
VENDOR: That's too bad. Like we say around here, like a toenail fungus, those shoes ain't going anywhere. We don't actually say that. It's an HR violation. Anyway, come on back though when you're ready for the odor of your idols.
SANDEN TOTTEN: Those shoes were pretty amazing.
MARC SANCHEZ: I know. Who knew there were so many different feet smells?
SANDEN TOTTEN: Yeah, I wonder how they figure it out all those people's foot stinks.
MARC SANCHEZ: And then how do they get the smells in the shoes? Is it like a spray or is it built into the fabric maybe or maybe the cool little--
MOLLY BLOOM: You're listening to Brains On from American Public Media. I'm Molly Bloom, and my co-host today is Lilia from Minneapolis. Hi, Lilia.
LILIA: Hey, Molly.
MOLLY BLOOM: So you have been listening to this podcast for a long time. You sent us your first question, I think five years ago, which is really amazing. And you recently sent us a letter asking us to do a show about body odor. And what specifically did you want to know?
LILIA: I wanted to know why certain parts of our body smell particularly worse than others.
MOLLY BLOOM: It's a really good question. I should also say that your letter was very beautifully illustrated and you can see that drawing on our Instagram brains_on. And in this drawing, you singled out three different smells.
LILIA: Stinky armpits, stinky breath, and stinky feet.
MOLLY BLOOM: Yes, and you are not the only one who wanted to know about these smells.
PAX: Hi, my name is Pax.
ISAAC: My name is Isaac and we are from Los Angeles, California.
PAX: Why does socks most stinky after you wear them?
JL: Hi, my name is JL and I'm from Louisville, Kentucky. Why are armpits sillier than the rest of the body?
MARSHAL: My name is Marshal and I'm from Ithaca, New York. And my question is, why are armpits stinky?
NICHOLAS: My name is Nicholas.
IKEA: And my name is Ikea.
BOTH (NICHOLAS AND IKEA): We are from Chino Hills, California. Our question is, why your feet smell?
MOLLY BLOOM: We will sniff out the nuances of these different smells in a bit. But first, did know there three different odors all come from the same source? They come from bacteria.
LILIA: Bacteria are tiny living things.
MOLLY BLOOM: So tiny, in fact, that each bacterium, that's how you say one bacteria, is made up of just one cell.
LILIA: And these cells come in all shapes and sizes. Some are shaped like rods.
MOLLY BLOOM: Others are shaped like balls.
LILIA: Some are even shaped like corkscrews.
MOLLY BLOOM: And they're so tiny you would need a microscope to see them.
LILIA: Which might be a good thing because guess what, you are covered in bacteria.
MOLLY BLOOM: In fact, if somehow you had super amazing zoom vision, you would see microscopic organisms on every inch of your body.
LILIA: Not just bacteria but also viruses and fungi.
MOLLY BLOOM: We call all these teensy things microbes.
LAURIE FLOWERS: The rough estimates put us at about 1 trillion actually microbes living on the surface of our skin.
LILIA: That's Laurie Flowers. She studies the microbes that hang out on our skin as a molecular microbiologist at the University of Pennsylvania.
MOLLY BLOOM: We also have microbes living inside of us and this motley crew of microbes has a pretty cool name. We call it your microbiome. When you count up all the microbes in and on our bodies, there are 10 times more microbes than there are cells that make up your body.
LILIA: And don't be eked out, they're actually super friendly and important.
MOLLY BLOOM: Scientists are just starting to learn about how they help us. Here's Dr. Heidi Kang, a dermatologist and scientist who studies these little thingies.
HEIDI KANG: Even though some microbes can cause infections, there are likely many good things that our microbes are doing. There have been some studies that have shown that our regular bacteria may protect us from other more infection causing bacteria from taking hold or staying in and on our bodies.
LILIA: So these friendly microbes protect us from unfriendly ones. And our skin gives back to them, too.
HEIDI KANG: We actually have on our skin nutrients for the microbes. For example, we have oils in our skin, sweat.
MOLLY BLOOM: Yum. Oil and sweat.
LILIA: Which brings us back to the stink.
MOLLY BLOOM: There are bacteria in your mouth that love to eat the food that gets stuck between your teeth.
BACTERIA 1: Broccoli particles, sugar molecules. Oh, some tiny bits of cheese. What a feast.
LILIA: And when these bacteria break down foods, they keep the parts they need for energy.
BACTERIA 1: Mine, mine, mine. All the energy is mine. Mine, mine, mine. All the energy is mine. Mine, mine, mine. All and the rest is mine. Hey, you can have that.
MOLLY BLOOM: Bacteria expel waste in the form of a gas, and sometimes that gas doesn't smell very good.
BACTERIA 1: You can have that.
LILIA: Bacteria in your guts do the same thing. That's what makes farts.
MOLLY BLOOM: So wait, does that mean stinky breath is like mouth farts?
BACTERIA 1: You can have that.
LILIA: It's best not to think too hard on it.
BACTERIA 1: This is delicious. I love living in your mouth. Mine, mine, mine. All the energy is mine.
LILIA: The same thing is happening on your feet and in your armpits, too.
MOLLY BLOOM: But since the source of the food and the environment of those body parts are a little different, they attract different kinds of bacteria. And those bacteria produce different kinds of smells.
BACTERIA 1: Yeah, us feet bacteria only like eating the stuff around your tootsies. That mouth stuff is gross.
BACTERIA 2: You're both gross. Eating armpit things is the only civilized way to be. Making energy, releasing gas. This is the life.
MOLLY BLOOM: But all of our microbiomes aren't exactly the same. Here's Dr. Heidi Kang again.
HEIDI KANG: What our studies have shown is each of us is a bit different from each other. So what might be found on one person may not be the exact same bacteria that is found on another person. But we also know that for individuals that live together, sometimes they can share microbes that are found on their skin.
So they may have some common microbes just because they live with each other or might be touching skin or shaking hands or hugging. Because of that, there are likely some bacteria or other microbes that go from one person to another.
MOLLY BLOOM: You might have the same eyes as your mom and the same bacteria on your feet.
LILIA: Speaking of feet, the bacteria there love to feast on oil and sweat.
MOLLY BLOOM: And different people have different amounts of sweat. Your shoes, socks, and the weather can play a role in foot smells too. And when your feet really work up a funk, it's usually because a few types of microbes have spread far and wide across the foot like an army taking over a kingdom.
LILIA: Oh, that reminds me of this recent episode of my favorite fantasy TV drama. Check it out.
NARRATOR: Somewhere in the Kingdom of Foot Strauss.
QUEEN TOOTSIE: There's a stink in the land and it's getting worse.
PLANTAR FASCIITIS: Yes, Queen Tootsie. I smell it too. It's the smell of bad tidings.
QUEEN TOOTSIE: No, Prince Plantar Fasciitis. It's bacteria. Stink producing bacteria. They've taken over the Kingdom of Foot Strauss might as well be the Kingdom of Feet Strauss. Eww.
PLANTAR FASCIITIS: My Lady, how did this happen?
QUEEN TOOTSIE: Winter. Winter came.
PLANTAR FASCIITIS: So?
QUEEN TOOTSIE: Don't you know anything about feet? When winter comes, the kingdom of Foot Strauss is shrouded in thick socks and shielded in large boots for months on end.
PLANTAR FASCIITIS: Yes, of course. But why again?
QUEEN TOOTSIE: To protect our dear friends from frostbite like Jon Toe and the other toes of the right swatch and the left swatch. Really to protect the toes, they watch both feet, both are important.
PLANTAR FASCIITIS: Yes, and also importantly, boots look cool.
QUEEN TOOTSIE: They do. But those bacteria they feed on sweat and oil. When were covered in thick socks and heavy boots, Foot Strauss get hot and sweaty. Air flow is low.
PLANTAR FASCIITIS: Indeed. The land has been quite moist, My Lady.
QUEEN TOOTSIE: And we are in the same boot day in and day out allowing sweat and dead skin to build up.
PLANTAR FASCIITIS: Yes, like that time Foot Strauss was constantly wearing a soccer cleat. Great floods of sweat back then he gods.
QUEEN TOOTSIE: It is a little known fact that on average a foot kingdom like ours has 25,000 sweat glands and makes about 1 cup of sweat a day.
PLANTAR FASCIITIS: I prefer one goblet of sweat. That's a little more my style.
QUEEN TOOTSIE: Oh, whatever. The boot we're in rarely lets in fresh air. And it's worn so much it never fully dries out. So those wretched bacteria have been feeding day after day. Building their ranks, making bad stank.
PLANTAR FASCIITIS: So what shall we do, Your Highness?
QUEEN TOOTSIE: I have a plan. We must cut off their food source. We must regularly wash Foot Strauss.
PLANTAR FASCIITIS: I took a bath once. It was horrifying.
QUEEN TOOTSIE: We must also change the socks frequently so they never carry too much sweat.
PLANTAR FASCIITIS: And I shall slay the socks with my sword.
QUEEN TOOTSIE: No. You shall wash the socks all of them with hot water preferably to kill any bacteria. And we shall air out the boots. Eventually the stink microbes will die back to manageable numbers, and more favorable less stinky bacteria will help reset the balance of Foot Strauss. Then the funk shall be finished.
PLANTAR FASCIITIS: Huzzah. Foot Strauss will rise again.
NARRATOR: Will the Queen's plan work? Will she be able to reduce the sweat and cut that foot stink down to size? Tune in next week to find out.
MOLLY BLOOM: Do you smell that?
LILIA: What?
MOLLY BLOOM: It smells like--
LILIA: Mystery sound.
MOLLY BLOOM: Oh, yes. The mystery sound. Are you ready, Lilia?
LILIA: Yes.
MOLLY BLOOM: All right. Here it is.
[ENGINE STARTS]
It's very short. So I think we should hear it at least one more time.
[ENGINE STARTS]
LILIA: It sounds like a lawn mower starting.
MOLLY BLOOM: Ooh, excellent guess. Well, we're going to be back with the answer in just a bit.
Right now, we're working on a series about feelings and we want your help. We want to know what certain emotions feel like to you. Lilia, what does it feel like in your body when you're happy?
LILIA: When I'm happy, it feels light and I want to move around as much as I can, like jump around and dance.
MOLLY BLOOM: I feel very similar when I'm happy. I just want to dance and move and do some jumping jacks which I don't normally want to do. So listeners, we'd love to hear what it feels like in your body when you're happy. You can send those answers to brainson.org/contact or you can also tell us what it feels like when you're nervous or sad or angry.
LILIA: All the fields.
MOLLY BLOOM: Send them to us at brainson.org/contact.
LILIA: That's where you can also send us your mystery sounds, drawings, high fives, and questions.
MOLLY BLOOM: Like this one.
KID: Hi, I am from Bolton, Massachusetts. And my question is, why do stink bugs stink?
LILIA: We'll answer that one during the Moment of Um at the end of the show.
MOLLY BLOOM: And I'll read the most recent list of names to be added to the Brains Honor Roll.
LILIA: Is the science of stinky stuff important to you and your family?
MOLLY BLOOM: If so, parents, please support Brains On. We're a nonprofit program and we need your help to keep doing what we do. Please go to brainson.org/donate and give any amount.
LILIA: Every cent helps us answer more questions.
MOLLY BLOOM: Thanks and high fives.
LILIA: Keep listening.
[THEME MUSIC PLAYING]
You're listening to Brains On from American Public Media. I'm Lilia.
MOLLY BLOOM: And I'm Molly. So we just learned about where these body smells come from.
LILIA: Thanks, bacteria. Normally, thank you. You're so helpful.
MOLLY BLOOM: We love our microbes here at Brains On. And that's made us wonder.
LILIA: Why is it that we find these body odors so unpleasant?
MOLLY BLOOM: We've asked neuroscientist Rachel Herz to help us figure it out.
LILIA: Hi, Rachel.
RACHEL HERZ: Hi, Lilia.
LILIA: You judged a rotten sneaker contest. Can you tell us about that?
RACHEL HERZ: I have had the fortune, so to speak, of doing this for a number of years. What this contest is about is it's kids from around the country ages 8 to 15, and they come together in New York City at Ripley's Believe It or Not museum at Times Square. I get to stick my nose as close as I possibly can manage into their sneakers and sniff what they've been doing and it's pretty disgusting.
LILIA: That smells-- that sounds really stinky.
RACHEL HERZ: It is really stinky. But I survive.
LILIA: How did you judge the smells?
RACHEL HERZ: Well, it's kind of a gut reaction. What I also like to call the trifecta of terrible which has to do with a combination of really bad smells in my opinion. One of the smells I find particularly grows is rotten fish. Often the kids who've have gotten to this level of the contest have been wading through streams or fishing and so they have a lot of fishy smells in their sneakers.
Another smell which I really don't like is chicken poop, and often these kids are from farms and so they often have chicken poop smell. And then there's the brew from both sweat and dirt and possibly dog poop. There's usually a third mystery factor that's a combination of different things. And so those three elements typically go into creating a concoction that's pretty awful.
LILIA: Why do we find body odors like stinky feet or armpits or breath to be gross?
RACHEL HERZ: Well, we consider them to be gross because they are emanations of other people's bodies. When we think about other people's bodies, we find that their secretions are generally disgusting because of the potential for them contaminating us. And this is related to being careful about not getting diseases.
So where this comes from is the avoidance of getting sick, which might happen if we're in close contact with other people. Their smells, for example, even though we don't get sick from their smells, could be an indication to us that the person is either not clean or not healthy and we don't want to be in contact with people who are unclean or unhealthy.
LILIA: Interesting. Do all humans find these smells gross or does it vary from person to person?
RACHEL HERZ: Well, that's a great question. Actually, it does generally vary from person to person in terms of what are the specific smells that we may find gross. However, when it comes to other people and smelling their body odor or their foot odor and armpit odor and things like that, we generally find, like I said, before the other to be offensive. Now, that being said, part of it has to do with your culture and your diet.
For example, if you have a diet that's rich in garlic and spices and things like that and if you smell those odors coming from other people, you might actually like those smells because they represent people from your community or your ethnic group or representing the foods that you love. But if you're not familiar with those smells and you don't eat those kinds of foods, then that could be a signal that those people aren't like you and that could be more of a turn off unfortunately.
MOLLY BLOOM: Does that mean that we don't find our own feet or armpits to smell bad as much?
RACHEL HERZ: We definitely do not consider our own smells to be anywhere near as bad as other peoples. The other thing is that we tend to be adapted or habituated to our own body odor in particular. We can't really smell ourselves anymore because we are exposed to how we smell constantly. Any smell that we're constantly exposed to, we actually stop being able to detect.
That's another reason why, for instance, in a more positive side of things, people who use a perfume or a cologne every day, they can smell that either because they just put it on every day. And because of that fact, their noses have actually gotten adapted to that smell and they're not detecting it anymore.
LILIA: Thanks for talking with us, Rachel.
RACHEL HERZ: Well, thank you for asking me questions.
MOLLY BLOOM: It was great to talk to you.
[THEME MUSIC PLAYING]
Let's go back to that mystery sound. Here it is again.
[ENGINE STARTING]
Let's hear it one more time.
[ENGINE STARTING]
Any new thoughts after hearing it again?
LILIA: Well, I still think it's a lawn mower starting or something close to that. But in the beginning, it sounds more like rustling or something.
MOLLY BLOOM: Yes, a very tricky sound. Here is the answer.
SADIE: Hi, my name is Sadie. I'm from Seattle, Washington. The sound you just heard was me dropping in my skateboard.
MOLLY BLOOM: It was a skateboard. And dropping in means going down the ramp. So you have seen those kind of like u-shaped ramps that people will skateboard on.
LILIA: Yeah.
MOLLY BLOOM: When you're at the top of it and you tip up your skateboard and then you go down. Here is Sadie describing it.
SADIE: Dropping in is when I start on the tail and rear wheels then lean forward to put the nose down. I have been skateboarding for three years. My favorite thing about skateboarding is the feeling of rolling on the board.
MOLLY BLOOM: Have you ever been skateboarding?
LILIA: No.
MOLLY BLOOM: It seems fun.
LILIA: My friends love it.
MOLLY BLOOM: Yeah, it seems like really fun and probably makes your socks a little sweaty.
LILIA: Yep.
MOLLY BLOOM: Maybe your feet a little stinky.
[THEME MUSIC PLAYING]
The bacteria that produce stinky smells love places that are dark, damp, and warm.
LILIA: That's why they might be more likely to live on your feet than on say the back of your hand.
MOLLY BLOOM: So naturally, these bacteria love armpits.
BACTERIA 2: Love is a strong word. 100% accurate, pits are perfection.
LILIA: And in your armpits, there are two different kinds of sweat glands.
MOLLY BLOOM: One is called an eccrine sweat gland. These make sweat even when you're very little, and its main job is to keep you cool.
LILIA: The other kind is called apocrine sweat gland. These glands produce sweat when you're stressed out.
MOLLY BLOOM: These ones don't start making sweat until your body starts changing from a kid's body into a grown up one.
BACTERIA 2: Apocrine sweat is like the caviar of sweat. It's delicious, refined, and well-balanced.
LILIA: And it's the sweat from these glands. The grown up apocrine glands that are responsible for the stink.
MOLLY BLOOM: Some of the kinds of bacteria that like to eat this kind of sweat make a very pungent byproduct called fire alcohol.
BACTERIA 2: Fire alcohols. Hard to spell, easy to smell. Here, take a whiff.
LILIA: They kind of have an oniony odor. When bodies start making these smells, people will often start wearing deodorant.
MOLLY BLOOM: Some of these deodorants work by wiping out the bacteria living in your armpits.
BACTERIA 2: After everything we've done for you, this is how you repay us?
MOLLY BLOOM: But as scientists learn more about all the good things bacteria in our skin microbiome do, they're trying to come up with new types of deodorant. Maybe something that would make us less stinky without harming the microbes that live on our bodies.
BACTERIA 2: Very much appreciated. Now, shall we make peace over a nice bottle of apocrine sweat? I think I have a 2008 Pinot Noir around here somewhere.
[PLOP]
Yes. Simply divine.
LILIA: The stinky smells that you detect on your breath, feet and armpits are made by bacteria.
MOLLY BLOOM: And our bodies are covered in all sorts of bacteria and other microbes.
LILIA: They make up our microbiome and it helps us in all sorts of ways. We're just starting to understand.
MOLLY BLOOM: That's it for this episode.
LILIA: Brains On is produced by Marc Sanchez, Sanden Totten, and Molly Bloom.
MOLLY BLOOM: Menaka Wilhelm is our fellow and her feet smell like wisteria blossoms. We had production help from Christina Lopez, Mitchell Johnson, and Betty Zhang and engineering help from Veronica Rodriguez and John Miller. Many thanks to Mindy and Chad Reger, Luke Burbank, Andrew Walsh, Tracy Mumford, Rosie DuPont, Doug Johnson and Taylor Kaufman.
LILIA: Now, before we go, it's time for a Moment of Um.
KID: My question is, why do stink bugs stink?
RICKY LARA: My name is Ricky Lara. I study a cool group of insects known as stink bugs at the University of California. There are more than 4,000 species of stink bugs in the world, altogether they are known for their notorious smell. And that's what I'm here to answer, what puts the stink in stink bugs. Stink bugs naturally produce different scents as part of their communication with organisms around them.
Some of those scents are chemicals that are part of their defense mechanism that kicks in when they sense a "predator" is near them. For example, when you approach a typical adult stink bug in the field that's sitting on a plant, the stink bugs will avoid the encounter by dropping to the ground or flying away and also releasing an odor as chemical from scent glands on its body.
In general, these chemicals are harmless to humans, but it's always a good idea to wash your hands after handling them. Now that why stink bugs stink, you might be wondering if they taste just as bad as they might smell.
So how do they taste? Stink bugs are a good source of protein for humans, and you'll be surprised to know that there are actually recipes for chocolate chip stink bug cookies, and even for stink bugs in salsa to pair with your favorite chips. That sounds appetizing, doesn't it?
MOLLY BLOOM: I'll tell you one thing that doesn't stink. It's this list of names. This is the Brains Honor Roll. This is how we thank all the brilliant minds who shared their ideas, questions, drawings and mystery sounds with us.
[LISTING HONOR ROLL]
[THEME MUSIC PLAYING]
We'll be back soon with more answers to your questions.
LILIA: Thanks for listening.
DUMINKA: Brains On is supported in part by a grant from the National Science Foundation.
VENDOR: Hi, welcome to Stink. We put the fun back in foot funk. Seriously, though, let me know if you want to try on any shoes. I personally recommend our new line of athletic stinkers. The smells are on-point.
MARC SANCHEZ: OK, thanks.
SANDEN TOTTEN: Oh. Hey, Marc. I didn't know you liked stinks too.
MARC SANCHEZ: Yeah, well, I somehow outgrew my shoes. The only ones I can wear are these neoprene booties from my wetsuit.
SANDEN TOTTEN: Me, too. I can only fit my feet in these wooden clogs right now.
MARC SANCHEZ: Do you think it was the experiments we were doing in the lab? Maybe it was when we were trying to grow a tomato that tastes like a pear.
SANDEN TOTTEN: It could have also been those tests we were doing to try to make our toes as sticky as gecko toes.
MARC SANCHEZ: Oh, yeah. That was fun. I hope my feet get back to normal. But I guess the upside is checking out some new foot smells.
VENDOR: Here at Stink, our motto is if you want to perform like the greats, having feet that smell like theirs is the first step.
MARC SANCHEZ: I'm thinking to try in the Serena Williams. Maybe I should go with a Venus. I don't know.
SANDEN TOTTEN: And the historical line is pretty cool, too. I wonder how they figured out what Gandhi's feet smelled like.
VENDOR: Oh, we actually have the world's leading stink scientists. And they've developed a cutting edge technique for recreating the foot scent of just about anybody. There's even talk of them winning a Nose Bell Prize. Am I right? Ready to try something on?
MARC SANCHEZ: I'd love to smell the Serena's please.
SANDEN TOTTEN: And I'll give the Lin-Manuel Miranda's a shot. Thank you.
VENDOR: Here we are. Great choices. So earthy. Can you get that the nose, that really great finish. These are, in fact, two of my personal favorite foot smells.
[SNIFFS]
Wow.
MARC SANCHEZ: With these shoes, I might have a couple of Broadway musicals in me.
SANDEN TOTTEN: Yeah, I may never be able to play Wimbledon, but I smell like I could--
MARC SANCHEZ: Hey, Molly. What's up?
MOLLY BLOOM: Oh, I'm here with Lilia.
LILIA: Marc, urgent news. Do you know that elixir you made to keep tacos upright at all times?
MARC SANCHEZ: Yeah, taco stand cement.
LILIA: We've been testing it, and it turns out it makes your feet grow.
MARC SANCHEZ: Oh, man. That's what it was.
LILIA: But luckily, it wears off after 71 hours and 37 and 1/2 minutes.
MARC SANCHEZ: That's great because we did those experiments 24, 48, exactly 71 hours and 36 minutes ago.
SANDEN TOTTEN: Bummer. I guess our feet will be back to normal soon and we won't need new shoes after all.
VENDOR: That's too bad. Like we say around here, like a toenail fungus, those shoes ain't going anywhere. We don't actually say that. It's an HR violation. Anyway, come on back though when you're ready for the odor of your idols.
SANDEN TOTTEN: Those shoes were pretty amazing.
MARC SANCHEZ: I know. Who knew there were so many different feet smells?
SANDEN TOTTEN: Yeah, I wonder how they figure it out all those people's foot stinks.
MARC SANCHEZ: And then how do they get the smells in the shoes? Is it like a spray or is it built into the fabric maybe or maybe the cool little--
MOLLY BLOOM: You're listening to Brains On from American Public Media. I'm Molly Bloom, and my co-host today is Lilia from Minneapolis. Hi, Lilia.
LILIA: Hey, Molly.
MOLLY BLOOM: So you have been listening to this podcast for a long time. You sent us your first question, I think five years ago, which is really amazing. And you recently sent us a letter asking us to do a show about body odor. And what specifically did you want to know?
LILIA: I wanted to know why certain parts of our body smell particularly worse than others.
MOLLY BLOOM: It's a really good question. I should also say that your letter was very beautifully illustrated and you can see that drawing on our Instagram brains_on. And in this drawing, you singled out three different smells.
LILIA: Stinky armpits, stinky breath, and stinky feet.
MOLLY BLOOM: Yes, and you are not the only one who wanted to know about these smells.
PAX: Hi, my name is Pax.
ISAAC: My name is Isaac and we are from Los Angeles, California.
PAX: Why does socks most stinky after you wear them?
JL: Hi, my name is JL and I'm from Louisville, Kentucky. Why are armpits sillier than the rest of the body?
MARSHAL: My name is Marshal and I'm from Ithaca, New York. And my question is, why are armpits stinky?
NICHOLAS: My name is Nicholas.
IKEA: And my name is Ikea.
BOTH (NICHOLAS AND IKEA): We are from Chino Hills, California. Our question is, why your feet smell?
MOLLY BLOOM: We will sniff out the nuances of these different smells in a bit. But first, did know there three different odors all come from the same source? They come from bacteria.
LILIA: Bacteria are tiny living things.
MOLLY BLOOM: So tiny, in fact, that each bacterium, that's how you say one bacteria, is made up of just one cell.
LILIA: And these cells come in all shapes and sizes. Some are shaped like rods.
MOLLY BLOOM: Others are shaped like balls.
LILIA: Some are even shaped like corkscrews.
MOLLY BLOOM: And they're so tiny you would need a microscope to see them.
LILIA: Which might be a good thing because guess what, you are covered in bacteria.
MOLLY BLOOM: In fact, if somehow you had super amazing zoom vision, you would see microscopic organisms on every inch of your body.
LILIA: Not just bacteria but also viruses and fungi.
MOLLY BLOOM: We call all these teensy things microbes.
LAURIE FLOWERS: The rough estimates put us at about 1 trillion actually microbes living on the surface of our skin.
LILIA: That's Laurie Flowers. She studies the microbes that hang out on our skin as a molecular microbiologist at the University of Pennsylvania.
MOLLY BLOOM: We also have microbes living inside of us and this motley crew of microbes has a pretty cool name. We call it your microbiome. When you count up all the microbes in and on our bodies, there are 10 times more microbes than there are cells that make up your body.
LILIA: And don't be eked out, they're actually super friendly and important.
MOLLY BLOOM: Scientists are just starting to learn about how they help us. Here's Dr. Heidi Kang, a dermatologist and scientist who studies these little thingies.
HEIDI KANG: Even though some microbes can cause infections, there are likely many good things that our microbes are doing. There have been some studies that have shown that our regular bacteria may protect us from other more infection causing bacteria from taking hold or staying in and on our bodies.
LILIA: So these friendly microbes protect us from unfriendly ones. And our skin gives back to them, too.
HEIDI KANG: We actually have on our skin nutrients for the microbes. For example, we have oils in our skin, sweat.
MOLLY BLOOM: Yum. Oil and sweat.
LILIA: Which brings us back to the stink.
MOLLY BLOOM: There are bacteria in your mouth that love to eat the food that gets stuck between your teeth.
BACTERIA 1: Broccoli particles, sugar molecules. Oh, some tiny bits of cheese. What a feast.
LILIA: And when these bacteria break down foods, they keep the parts they need for energy.
BACTERIA 1: Mine, mine, mine. All the energy is mine. Mine, mine, mine. All the energy is mine. Mine, mine, mine. All and the rest is mine. Hey, you can have that.
MOLLY BLOOM: Bacteria expel waste in the form of a gas, and sometimes that gas doesn't smell very good.
BACTERIA 1: You can have that.
LILIA: Bacteria in your guts do the same thing. That's what makes farts.
MOLLY BLOOM: So wait, does that mean stinky breath is like mouth farts?
BACTERIA 1: You can have that.
LILIA: It's best not to think too hard on it.
BACTERIA 1: This is delicious. I love living in your mouth. Mine, mine, mine. All the energy is mine.
LILIA: The same thing is happening on your feet and in your armpits, too.
MOLLY BLOOM: But since the source of the food and the environment of those body parts are a little different, they attract different kinds of bacteria. And those bacteria produce different kinds of smells.
BACTERIA 1: Yeah, us feet bacteria only like eating the stuff around your tootsies. That mouth stuff is gross.
BACTERIA 2: You're both gross. Eating armpit things is the only civilized way to be. Making energy, releasing gas. This is the life.
MOLLY BLOOM: But all of our microbiomes aren't exactly the same. Here's Dr. Heidi Kang again.
HEIDI KANG: What our studies have shown is each of us is a bit different from each other. So what might be found on one person may not be the exact same bacteria that is found on another person. But we also know that for individuals that live together, sometimes they can share microbes that are found on their skin.
So they may have some common microbes just because they live with each other or might be touching skin or shaking hands or hugging. Because of that, there are likely some bacteria or other microbes that go from one person to another.
MOLLY BLOOM: You might have the same eyes as your mom and the same bacteria on your feet.
LILIA: Speaking of feet, the bacteria there love to feast on oil and sweat.
MOLLY BLOOM: And different people have different amounts of sweat. Your shoes, socks, and the weather can play a role in foot smells too. And when your feet really work up a funk, it's usually because a few types of microbes have spread far and wide across the foot like an army taking over a kingdom.
LILIA: Oh, that reminds me of this recent episode of my favorite fantasy TV drama. Check it out.
NARRATOR: Somewhere in the Kingdom of Foot Strauss.
QUEEN TOOTSIE: There's a stink in the land and it's getting worse.
PLANTAR FASCIITIS: Yes, Queen Tootsie. I smell it too. It's the smell of bad tidings.
QUEEN TOOTSIE: No, Prince Plantar Fasciitis. It's bacteria. Stink producing bacteria. They've taken over the Kingdom of Foot Strauss might as well be the Kingdom of Feet Strauss. Eww.
PLANTAR FASCIITIS: My Lady, how did this happen?
QUEEN TOOTSIE: Winter. Winter came.
PLANTAR FASCIITIS: So?
QUEEN TOOTSIE: Don't you know anything about feet? When winter comes, the kingdom of Foot Strauss is shrouded in thick socks and shielded in large boots for months on end.
PLANTAR FASCIITIS: Yes, of course. But why again?
QUEEN TOOTSIE: To protect our dear friends from frostbite like Jon Toe and the other toes of the right swatch and the left swatch. Really to protect the toes, they watch both feet, both are important.
PLANTAR FASCIITIS: Yes, and also importantly, boots look cool.
QUEEN TOOTSIE: They do. But those bacteria they feed on sweat and oil. When were covered in thick socks and heavy boots, Foot Strauss get hot and sweaty. Air flow is low.
PLANTAR FASCIITIS: Indeed. The land has been quite moist, My Lady.
QUEEN TOOTSIE: And we are in the same boot day in and day out allowing sweat and dead skin to build up.
PLANTAR FASCIITIS: Yes, like that time Foot Strauss was constantly wearing a soccer cleat. Great floods of sweat back then he gods.
QUEEN TOOTSIE: It is a little known fact that on average a foot kingdom like ours has 25,000 sweat glands and makes about 1 cup of sweat a day.
PLANTAR FASCIITIS: I prefer one goblet of sweat. That's a little more my style.
QUEEN TOOTSIE: Oh, whatever. The boot we're in rarely lets in fresh air. And it's worn so much it never fully dries out. So those wretched bacteria have been feeding day after day. Building their ranks, making bad stank.
PLANTAR FASCIITIS: So what shall we do, Your Highness?
QUEEN TOOTSIE: I have a plan. We must cut off their food source. We must regularly wash Foot Strauss.
PLANTAR FASCIITIS: I took a bath once. It was horrifying.
QUEEN TOOTSIE: We must also change the socks frequently so they never carry too much sweat.
PLANTAR FASCIITIS: And I shall slay the socks with my sword.
QUEEN TOOTSIE: No. You shall wash the socks all of them with hot water preferably to kill any bacteria. And we shall air out the boots. Eventually the stink microbes will die back to manageable numbers, and more favorable less stinky bacteria will help reset the balance of Foot Strauss. Then the funk shall be finished.
PLANTAR FASCIITIS: Huzzah. Foot Strauss will rise again.
NARRATOR: Will the Queen's plan work? Will she be able to reduce the sweat and cut that foot stink down to size? Tune in next week to find out.
MOLLY BLOOM: Do you smell that?
LILIA: What?
MOLLY BLOOM: It smells like--
LILIA: Mystery sound.
MOLLY BLOOM: Oh, yes. The mystery sound. Are you ready, Lilia?
LILIA: Yes.
MOLLY BLOOM: All right. Here it is.
[ENGINE STARTS]
It's very short. So I think we should hear it at least one more time.
[ENGINE STARTS]
LILIA: It sounds like a lawn mower starting.
MOLLY BLOOM: Ooh, excellent guess. Well, we're going to be back with the answer in just a bit.
Right now, we're working on a series about feelings and we want your help. We want to know what certain emotions feel like to you. Lilia, what does it feel like in your body when you're happy?
LILIA: When I'm happy, it feels light and I want to move around as much as I can, like jump around and dance.
MOLLY BLOOM: I feel very similar when I'm happy. I just want to dance and move and do some jumping jacks which I don't normally want to do. So listeners, we'd love to hear what it feels like in your body when you're happy. You can send those answers to brainson.org/contact or you can also tell us what it feels like when you're nervous or sad or angry.
LILIA: All the fields.
MOLLY BLOOM: Send them to us at brainson.org/contact.
LILIA: That's where you can also send us your mystery sounds, drawings, high fives, and questions.
MOLLY BLOOM: Like this one.
KID: Hi, I am from Bolton, Massachusetts. And my question is, why do stink bugs stink?
LILIA: We'll answer that one during the Moment of Um at the end of the show.
MOLLY BLOOM: And I'll read the most recent list of names to be added to the Brains Honor Roll.
LILIA: Is the science of stinky stuff important to you and your family?
MOLLY BLOOM: If so, parents, please support Brains On. We're a nonprofit program and we need your help to keep doing what we do. Please go to brainson.org/donate and give any amount.
LILIA: Every cent helps us answer more questions.
MOLLY BLOOM: Thanks and high fives.
LILIA: Keep listening.
[THEME MUSIC PLAYING]
You're listening to Brains On from American Public Media. I'm Lilia.
MOLLY BLOOM: And I'm Molly. So we just learned about where these body smells come from.
LILIA: Thanks, bacteria. Normally, thank you. You're so helpful.
MOLLY BLOOM: We love our microbes here at Brains On. And that's made us wonder.
LILIA: Why is it that we find these body odors so unpleasant?
MOLLY BLOOM: We've asked neuroscientist Rachel Herz to help us figure it out.
LILIA: Hi, Rachel.
RACHEL HERZ: Hi, Lilia.
LILIA: You judged a rotten sneaker contest. Can you tell us about that?
RACHEL HERZ: I have had the fortune, so to speak, of doing this for a number of years. What this contest is about is it's kids from around the country ages 8 to 15, and they come together in New York City at Ripley's Believe It or Not museum at Times Square. I get to stick my nose as close as I possibly can manage into their sneakers and sniff what they've been doing and it's pretty disgusting.
LILIA: That smells-- that sounds really stinky.
RACHEL HERZ: It is really stinky. But I survive.
LILIA: How did you judge the smells?
RACHEL HERZ: Well, it's kind of a gut reaction. What I also like to call the trifecta of terrible which has to do with a combination of really bad smells in my opinion. One of the smells I find particularly grows is rotten fish. Often the kids who've have gotten to this level of the contest have been wading through streams or fishing and so they have a lot of fishy smells in their sneakers.
Another smell which I really don't like is chicken poop, and often these kids are from farms and so they often have chicken poop smell. And then there's the brew from both sweat and dirt and possibly dog poop. There's usually a third mystery factor that's a combination of different things. And so those three elements typically go into creating a concoction that's pretty awful.
LILIA: Why do we find body odors like stinky feet or armpits or breath to be gross?
RACHEL HERZ: Well, we consider them to be gross because they are emanations of other people's bodies. When we think about other people's bodies, we find that their secretions are generally disgusting because of the potential for them contaminating us. And this is related to being careful about not getting diseases.
So where this comes from is the avoidance of getting sick, which might happen if we're in close contact with other people. Their smells, for example, even though we don't get sick from their smells, could be an indication to us that the person is either not clean or not healthy and we don't want to be in contact with people who are unclean or unhealthy.
LILIA: Interesting. Do all humans find these smells gross or does it vary from person to person?
RACHEL HERZ: Well, that's a great question. Actually, it does generally vary from person to person in terms of what are the specific smells that we may find gross. However, when it comes to other people and smelling their body odor or their foot odor and armpit odor and things like that, we generally find, like I said, before the other to be offensive. Now, that being said, part of it has to do with your culture and your diet.
For example, if you have a diet that's rich in garlic and spices and things like that and if you smell those odors coming from other people, you might actually like those smells because they represent people from your community or your ethnic group or representing the foods that you love. But if you're not familiar with those smells and you don't eat those kinds of foods, then that could be a signal that those people aren't like you and that could be more of a turn off unfortunately.
MOLLY BLOOM: Does that mean that we don't find our own feet or armpits to smell bad as much?
RACHEL HERZ: We definitely do not consider our own smells to be anywhere near as bad as other peoples. The other thing is that we tend to be adapted or habituated to our own body odor in particular. We can't really smell ourselves anymore because we are exposed to how we smell constantly. Any smell that we're constantly exposed to, we actually stop being able to detect.
That's another reason why, for instance, in a more positive side of things, people who use a perfume or a cologne every day, they can smell that either because they just put it on every day. And because of that fact, their noses have actually gotten adapted to that smell and they're not detecting it anymore.
LILIA: Thanks for talking with us, Rachel.
RACHEL HERZ: Well, thank you for asking me questions.
MOLLY BLOOM: It was great to talk to you.
[THEME MUSIC PLAYING]
Let's go back to that mystery sound. Here it is again.
[ENGINE STARTING]
Let's hear it one more time.
[ENGINE STARTING]
Any new thoughts after hearing it again?
LILIA: Well, I still think it's a lawn mower starting or something close to that. But in the beginning, it sounds more like rustling or something.
MOLLY BLOOM: Yes, a very tricky sound. Here is the answer.
SADIE: Hi, my name is Sadie. I'm from Seattle, Washington. The sound you just heard was me dropping in my skateboard.
MOLLY BLOOM: It was a skateboard. And dropping in means going down the ramp. So you have seen those kind of like u-shaped ramps that people will skateboard on.
LILIA: Yeah.
MOLLY BLOOM: When you're at the top of it and you tip up your skateboard and then you go down. Here is Sadie describing it.
SADIE: Dropping in is when I start on the tail and rear wheels then lean forward to put the nose down. I have been skateboarding for three years. My favorite thing about skateboarding is the feeling of rolling on the board.
MOLLY BLOOM: Have you ever been skateboarding?
LILIA: No.
MOLLY BLOOM: It seems fun.
LILIA: My friends love it.
MOLLY BLOOM: Yeah, it seems like really fun and probably makes your socks a little sweaty.
LILIA: Yep.
MOLLY BLOOM: Maybe your feet a little stinky.
[THEME MUSIC PLAYING]
The bacteria that produce stinky smells love places that are dark, damp, and warm.
LILIA: That's why they might be more likely to live on your feet than on say the back of your hand.
MOLLY BLOOM: So naturally, these bacteria love armpits.
BACTERIA 2: Love is a strong word. 100% accurate, pits are perfection.
LILIA: And in your armpits, there are two different kinds of sweat glands.
MOLLY BLOOM: One is called an eccrine sweat gland. These make sweat even when you're very little, and its main job is to keep you cool.
LILIA: The other kind is called apocrine sweat gland. These glands produce sweat when you're stressed out.
MOLLY BLOOM: These ones don't start making sweat until your body starts changing from a kid's body into a grown up one.
BACTERIA 2: Apocrine sweat is like the caviar of sweat. It's delicious, refined, and well-balanced.
LILIA: And it's the sweat from these glands. The grown up apocrine glands that are responsible for the stink.
MOLLY BLOOM: Some of the kinds of bacteria that like to eat this kind of sweat make a very pungent byproduct called fire alcohol.
BACTERIA 2: Fire alcohols. Hard to spell, easy to smell. Here, take a whiff.
LILIA: They kind of have an oniony odor. When bodies start making these smells, people will often start wearing deodorant.
MOLLY BLOOM: Some of these deodorants work by wiping out the bacteria living in your armpits.
BACTERIA 2: After everything we've done for you, this is how you repay us?
MOLLY BLOOM: But as scientists learn more about all the good things bacteria in our skin microbiome do, they're trying to come up with new types of deodorant. Maybe something that would make us less stinky without harming the microbes that live on our bodies.
BACTERIA 2: Very much appreciated. Now, shall we make peace over a nice bottle of apocrine sweat? I think I have a 2008 Pinot Noir around here somewhere.
[PLOP]
Yes. Simply divine.
LILIA: The stinky smells that you detect on your breath, feet and armpits are made by bacteria.
MOLLY BLOOM: And our bodies are covered in all sorts of bacteria and other microbes.
LILIA: They make up our microbiome and it helps us in all sorts of ways. We're just starting to understand.
MOLLY BLOOM: That's it for this episode.
LILIA: Brains On is produced by Marc Sanchez, Sanden Totten, and Molly Bloom.
MOLLY BLOOM: Menaka Wilhelm is our fellow and her feet smell like wisteria blossoms. We had production help from Christina Lopez, Mitchell Johnson, and Betty Zhang and engineering help from Veronica Rodriguez and John Miller. Many thanks to Mindy and Chad Reger, Luke Burbank, Andrew Walsh, Tracy Mumford, Rosie DuPont, Doug Johnson and Taylor Kaufman.
LILIA: Now, before we go, it's time for a Moment of Um.
KID: My question is, why do stink bugs stink?
RICKY LARA: My name is Ricky Lara. I study a cool group of insects known as stink bugs at the University of California. There are more than 4,000 species of stink bugs in the world, altogether they are known for their notorious smell. And that's what I'm here to answer, what puts the stink in stink bugs. Stink bugs naturally produce different scents as part of their communication with organisms around them.
Some of those scents are chemicals that are part of their defense mechanism that kicks in when they sense a "predator" is near them. For example, when you approach a typical adult stink bug in the field that's sitting on a plant, the stink bugs will avoid the encounter by dropping to the ground or flying away and also releasing an odor as chemical from scent glands on its body.
In general, these chemicals are harmless to humans, but it's always a good idea to wash your hands after handling them. Now that why stink bugs stink, you might be wondering if they taste just as bad as they might smell.
So how do they taste? Stink bugs are a good source of protein for humans, and you'll be surprised to know that there are actually recipes for chocolate chip stink bug cookies, and even for stink bugs in salsa to pair with your favorite chips. That sounds appetizing, doesn't it?
MOLLY BLOOM: I'll tell you one thing that doesn't stink. It's this list of names. This is the Brains Honor Roll. This is how we thank all the brilliant minds who shared their ideas, questions, drawings and mystery sounds with us.
[LISTING HONOR ROLL]
[THEME MUSIC PLAYING]
We'll be back soon with more answers to your questions.
LILIA: Thanks for listening.
Transcription services provided by 3Play Media.
