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JOE PALCA, host:

From NPR News, this is Talk of the Nation: Science Friday. I'm Joe Palca. For the rest of this hours, the science of smell. From a whiff of morning coffee and some minty toothpaste onto car exhaust and your coworker's bad breath, your day is filled with smells, fruity, earthy, floral, skunk-y, all of them sending a signal or maybe a warning and telling your brain something about the world around you.

Of the five senses, none is as evocative and as elusive as smell. No one has come up with a reliable estimate of the number of scents in the world or a good way to classify them, but that hasn't stopped scientists from studying the aromas that drive, scare or signal us, or simply take us back to a long-forgotten memory. My next guest makes his living studying smell and how it affects us and he's written a book on the subject. Avery Gilbert is the author of "What the Nose Knows" - Get it? Nose knows? - "The Science of Scent in Everyday Life," just out by Crown Publishers. He's a psychologist and smell scientist, and he joins me here in the NPR bureau. Welcome to Science Friday, Dr. Gilbert.

Dr. AVERY GILBERT (Author, "What the Nose Knows: The Science of Scent in Everyday Life"): Thanks, Joe.

PALCA: And we'd like to hear - we're going to be interested in hearing your thoughts on smell. So, by all means, give us a call, 800-989-8255. That's 800-989-TALK. And yeah, there's also some interesting links on our website, sciencefriday.com, and you know, I was just talking about, is smell sort of the Rodney Dangerfield of the senses, it doesn't get no respect?

Dr. GILBERT: It was the last to be explored, and only now do we actually have a sense of what the external wiring is. Back in 2004, the Nobel Prize in medicine and physiology went to Linda Buck and Richard Axel for finding the nature of the receptors that - actually high up on our nasal tissue, contact the odor molecules when they come in, and turns out to be a huge gene family, an enormous number of different receptors. Now, we have a sense of what the wiring is, and we're kind of following it up into the brain and the psychology of the matter.

PALCA: Well, tell us a little bit about - I mean, how does - how is smell generated? Take us through from odor to sensation.

Dr. GILBERT: Well, an odor is a volatile molecule. It has to be light enough to float in the air and be inhaled up your nose, where it goes very high up in the nasal passages to a set of - a little patch of tissue about the size of a dime that has sensory cells with little tendrils, spaghetti-like tendrils, on which are receptors. You could think of them like a baseball mitt, and the smell molecules is the baseball. When the baseball hits, it stimulates the cell to send a signal up into the brain. So, that's the key first step, where you take chemical message and translate it into electrical message to the brain.

PALCA: OK. And if there's these large number of receptors, and this mix that goes up to the brain, why has it proven so hard to categorize these things? I mean, for example, taste. We have five tastes, or color, we have primary colors, vision. Why has smell proven so elusive?

Dr. GILBERT: At a practical level, it's very difficult to measure. Scientists have had a hard time developing ways to present a standardized smell, for example. There's no kilogram of patchouli, in that sense. There's no - so it's a nuisance in a laboratory. But more specifically, it's trying to come up with a categorization. We don't have a standardized rainbow, in the same way that we have the Newtonian rainbow. You know, colors, wavelengths of physical light in the real world are continuous, variable, and it's our brain that creates the rainbow - the colors of the rainbow. In the same way, our brain is creating odor categories, but it's - we haven't yet specified them in a way that's useful in a laboratory.

PALCA: Now, you talk about a device that's critical for odor chemists, this thing called a gas chromatograph, which actually takes the volatile elements in a particular thing and separates it into different chemical characteristics. Can you look at the output from a gas chromatograph and say, oh, that's an orange or oh, that's a peach? Or is it - there's something else going on in terms of how we perceive these things?

Dr. GILBERT: A gas chromatograph, coupled with what's called mass spectrophotometry, enables you to do that. What you get is a chart that has little peaks on it, and those peaks and valleys are the odor fingerprint, if you will. And a trained chemist, somebody who's skilled in analyzing different sorts of samples, can look at a set of peaks and say that's probably a citrus fruit, and it's probably an orange. But you or I couldn't.

PALCA: But the cool thing is, and this is - you described this in the book. OK. So we have actually - so we can do some real-life thing. We've got a lime here, a lime with an earthworm...

(Soundbite of laughter)

PALCA: That's not an earthworm, an inchworm. So, OK. So, this is a slice of lime and...

(Soundbite of sniffing)

PALCA: Now, that definitely smells like lime. So it's a lime. But if you wanted to create an artificial lime, you wouldn't have to have all the chemicals in line to make me think I'm smelling a lime, right?

Dr. GILBERT: That's an interesting payoff of all the research has been done since about the late '70s on chemical constituents of natural materials. So people have examined all kinds of food, raw fish, cooked fish, vegetables, fruits, and found the same molecules keep turning up again and again. And in fact, Terry Acree, a professor of food science at Cornell, has found that probably less than 1,000 different molecules enable you to recreate any natural cell in the world.

PALCA: Huh. And that was one other thing I wanted to point out. I mean, and we were talking about this earlier. So when I held this lime up to my nose...

(Soundbite of sniffing)

PALCA: I was sniffing at it, and that's how you get the air - the volatile molecules up into the back of a nose where those receptors are sitting, waiting for whatever the smell is. But you described there's different kinds of sniffers. Am I a typical sniffer or atypical sniffer?

Dr. GILBERT: You're a moderate sort of sniffer.

PALCA: Moderate sniffer.

Dr. GILBERT: Yeah. There's some people who are very delicate. If you hand them a new smell in a bottle, they'll just take tentative little sniffs, and other people, like all kind of honkers, who are just...

(Soundbite of sniffing)

Dr. GILBERT: You know, really just inhaling again and again and again. I think they're going to hurt themselves. And every person has a kind of typical way of sampling smell. And again, you know, you can tell behind the - when I test subjects behind the screen, I can hear on the other side of the screen how they're sniffing, and I know if somebody takes 20 minutes of big honking sniffs, it's going to be a long day in the test lab.

(Soundbite of laughter)

PALCA: I'm just wondering now that, you know, so with loud sounds, you can damage your ear cells and the inner ear. With bright light, you can damage the retinal cells. Are there smells that are so powerful that it can knock out your sensors?

Dr. GILBERT: Not really as smells. I mean, if you, you know, if you get a face full of pure chlorine in an industrial accident or something, you can burn your tissues, but that's at the extreme.

PALCA: OK, all right, interesting. Well, I'm sure our listeners have a lot of questions that they'd like to ask. And so, let me remind everyone the number is 800-989-8255. That's 800-98-TALK. And let's take a call now from Ryan in Greenville - is it Michigan?

RYAN (Caller): Yes, it is.

PALCA: Welcome to the program, Ryan.

RYAN: Thanks for taking my question. I've heard in the news recently about the possibility of electronic transmission of smells, and I was just curious how that was possible, how the chemicals could be reproduced.

PALCA: All right. Thanks for that call, Ryan. Electronic transmission of smells.

Dr. GILBERT: Well, actually, I was involved in a startup company some years back that was attempting to do just that. Basically, the idea is that you get a code, and you can make codes for different smells in the same way graphic artists have codes for different sorts of colors, and the code would correspond to firing off a little set of chemicals in a pallet, in a, say, computer peripheral, and so, you could click on a perfume ad, say, on a screen, and somewhere else, the code will fire a little device next to you and you get a puff of that fragrance. So it's all in the software.

PALCA: There was actually - you mentioned on the book, which - and we were trying with doing something like this, the idea that you could transmit smells over the radio, and of course, right now, you can't, or at least not without specialized equipment on the receiving end. But you talk about somebody who played a joke on the audience once where he said, I'm going to play a tone now and you should smell something and call us and tell us what you think you smelled. And people called in and said, oh, I smell bacon or I smell something. And they were actually lulled into thinking they could smell something.

Dr. GILBERT: Yeah. It was Michael O'Mahney's (ph) famous experiment in BBC in England. There a lot of expectation that goes into what we smell, so it can bias us to expect certain things, good or bad. And in fact, you know, you were smelling a lime. In consumer products that are lemon-flavored, the expectation is that it - consumers more than just a simple lemon. If you actually get a simple lemon smell, it's naturally accurate, they're going to be disappointment. So most lemon products tastes - smell like grapefruit.

(Soundbite of laughter)

PALCA: OK. I'm sorry. I want to take another call, but I have to say, the other that really amazed me is that your smell is also affected by your expectation in terms of look, and you describe people who - you pour the same wine into two different kinds of glasses, and they smell it in a different glasses, and they think it's two different wines, even though all they're changing is the glass, and they're...

Dr. GILBERT: That's right, and if you have two different solutions with a smell in it and you put a little food coloring in one and other is clear, people sniffing the food-colored one will think it smells stronger.

PALCA: Interesting. All right, let's take another call now and let's go to Ken in Houston, Texas. Ken, welcome to Science Friday.

KEN (Caller): Hi. Thank you. I noticed when I about 13 years old that I didn't really have a sense of smell, and at the time, no one actually believed me. But was hoping your guest could talk about that, what causes that and how common that is.

PALCA: All right.

Dr. GILBERT: Well...

PALCA: No smell at all or no sense of smell at all.

Dr. GILBERT: Well, I guess...

KEN: Well, a really impaired sense. I mean, some very strong odors like ammonia I can detect. But often, (unintelligible). I really don't know what they're talking about.

PALCA: Got it. All right.

Dr. GILBERT: It's rare, but it's happened. I've met other people like yourself. When you're smelling ammonia, actually that's not the olfactory nerve. That's the chemosensory nerves in your nose, the same way you might be able to smell vinegar or feel the chili pepper burn on your tongue and on your lips. So it's rare. It happens. Other people have lost sense of smell by a slight blow to the head, for example, or a bad flu. So I guess you've never really known what you've lost in a way. So you might be prognostically better off than people who've known it and then lost it suddenly, I'm guessing.

PALCA: Ken, thanks very much for the call.

KEN: Well, thank you.

PALCA: OK. Let's take another call now and go to - let me see here. Is it Judy in Portland, Oregon? Judy, welcome to Science Friday.

JUDY (Caller): Hi, there!

PALCA: Hi!

JUDY: This is really interesting. I was telling the guy that, you know, was taking the calls from people that my big smell that I love is vanilla. And inevitably, when I'm at a perfume counter and they're trying to sell me a new kind of perfume, I'll go, oh, that's got vanilla in it, doesn't it? And sure, you know, sure enough, it does have vanilla in it. There's something about vanilla, even if it's masked slightly by musk or a floral smell, I inevitably smell the vanilla. And I was curious as to, you know, what causes that? I mean, just a personal preference or if there really is something in your chemical makeup in the nose that lends you to smell a particular smell?

Dr. GILBERT: Well, in the industry, vanilla's kind of notorious for being very - it penetrates through other combinations. That's why in the vanilla-scented or vanilla-themed perfumes, for example, are mainly vanilla. It's hard to work with it. And in itself in a laboratory, it'll leak out of any bottle. It'll go through plastic. It's just quite an aggressive smell.

PALCA: You know, the other thing, speaking of vanilla, as I was doing some interviews with winemakers in Bordeaux, and they were saying that if they want to make a wine popular, they'll put a little vanilla flavor in it because it makes people like the wine better.

Dr. GILBERT: That's right. There was a period where vanilla notes were very popular in colognes or perfumes, well, mainly perfumes for women, because they had a kind of edible quality. You smell that, you think cookies, you think sweetness, and it's very innocent and so especially for a lot younger wearing fragrances, it's a popular ingredient.

PALCA: But you know, just that last sentence you just said is really interesting, because you used "notes" which is usually a term associated with music and hearing and "edible" as in taste. So as if the smell can't stand on its own, it sort of has to rope in other senses which I think is just an interesting thing about smell.

Dr. GILBERT: We're always groping for metaphors with smell, but perfumers tend to talk about notes for individual ingredients, and they talk about chords or a chord which are combinations of two or three such things. And since we got a very musical sense to it, there's a guy back in the 19th century who had the idea that smell worked in a musical system, and there was kind of an octave system he had all worked out. I don't know he pulled it out of his head. He really had no basis, in fact, but it was an interesting idea.

PALCA: We're talking with Avery Gilbert. He's the author of "What the Nose Knows: The Science of Scent in Everyday Life." I'm Joe Palca and this is Talk of the Nation from NPR News. And let's take another call now and go to Christie in Novato, California. Christie, welcome to Science Friday.

CHRISTIE (Caller): Hi! Thank you.

PALCA: You bet.

CHRISTIE: I am a mom of two young boys and I am fascinated with the smell of baby heads, and I'm not the only one, because even when you pass off your baby to someone else, they go oh, the baby smell. And then somewhere between, I don't know, two or three years they seem to lose that smell. It turns into a different one. So I've always kind of wondered about that. I assume it's something, pheromones, bonding, but I would like to know if you know anything about that.

PALCA: Cool! Interesting question. Thanks, Christie.

Dr. GILBERT: It's a great question. I hear it a lot, and I've experienced it with my own kids. There's that kind of clean baby skin smell that you get from young kids, and then I don't know if it's like they grow out of it. I think it has to do also with diet and things like that. I mean, to get indelicate with baby poop from nursing infants is fairly inoffensive. You start feeding them the solids foods and then the diaper changing becomes something you want your spouse to do. I think it's a lifelong process as well. Some recent work shows that there are reliable changes in character of body odors. People age from middle age and on. So that's just one of the many things as being kind of worked out now.

PALCA: You know, one of the other things you talk about in the book is how mothers can recognize their baby smell and find it pleasanter than other babies, even when it comes to baby poop.

Dr. GILBERT: That's right. It's not just yes, using baby poop samples from the various kids in the nursery. It's not just mom thinking her kid smells better or less worse than the rest. You can actually - you can back it up.

PALCA: That's cool. We have time for one more quick call now, Kathleen from Rochester Hills, Michigan. Welcome to the program.

KATHLEEN (Caller): Thank you. Yes. My husband has an absolutely awesome sense of smell, and it can also be kind of a detriment, he says. And I always tease him and say, well, maybe we can find out if there are other ways you can make money with that. Are there opportunities out there for such things where research labs utilize people with extra sensory that way?

PALCA: Kathleen, thanks. Interesting question. What about that?

Dr. GILBERT: Sure. Yes. He's got a future in quality control. I mean, you have to smell materials in the food industry, fragrance industry to make sure they're in spec, make sure something is not off. I mean, you could be a cheese inspector.

PALCA: Are there, you know, - I've heard about super tasters. Are there super smellers? Or do we know?

Dr. GILBERT: There are tons of super smellers in fiction all over the place. Salman Rushdie has written about them. That strange German novel "Perfume: The Story of a Murderer" is about it. But in real life, they don't exist and the strange thing is that in terms of testing sense of smell, all the tests, the best you can achieve on them is being average and normal. There's no test that shows that you're a smell genius. In fact, it's very hard to define.

PALCA: Yes. Can you get better?

Dr. GILBERT: Yes, absolutely. It's a matter of training, the same way that wine tasting, if you have enough samples, you know, presented to you repeatedly and described to you. You build your own kind of internal memory system for it, and you can learn it. It's very rarely a case of perfumers are good just because of their physical nose. It's their brain.

PALCA: And there's one other issue and we only have a few seconds before the break. But humans versus dogs. Are dogs much better than we are? Are we as terrible as we think or...

Dr. GILBERT: We're not as terrible as we think. And in fact, in many instances we're on a par with dogs, surprisingly enough. Although there are differences in how we function, but for pure detection, we're close.

PALCA: Really? Is there one species that is like the smelling king of the animal world?

Dr. GILBERT: I'm not sure...

PALCA: I stumped him. That's great.

Dr. GILBERT: Well, no. I'm a real proponent that we're up there.

PALCA: OK. All right. Well, you know, that's good. We've got to be good for something as human beings. I think it's fine if we are good at being smellers. OK. We're going to keep thinking about smell for the rest of this hour and we're going to talk to a curator of an interesting exhibit that's currently under way in Philadelphia. So stay with us. We'll be right back after a short break.

(Soundbite of music)

PALCA: This hour, we're talking about smell. My guest is Avery Gilbert. He's a psychologist and smell scientist, and author of "What the Nose Knows: The Science of Scent in Everyday Life." And smell might not be the first thing you think of when it comes to work of art. But for my next guest, the olfactory experience is the art form. Jim Drobnick is co-curator of the Odor Limits exhibition. You have one more day to take it in so hurry. It's now showing or smelling at the Esther M. Klein Art Gallery at the Science Center in Philadelphia. Unfortunately, it closes tomorrow. But maybe Mr. Drobnick can tell us about it and see if it'll be somewhere else. Welcome to the program, sir.

Mr. JIM DROBNICK (Co-Curator, Odor Limits Exhibition, Philadelphia Science Center): Oh, good. Well, thank you very much. It's a pleasure.

PALCA: And if you'd like to ask questions about smell and this exhibit, please call us. The number is 800-989-8255. That's 800-989-Talk. Why an art exhibit about smell? What were you trying to get at?

Mr. DROBNICK: Well, it's an alternative way for artists to engage viewers and visitors. Smell is one of those sensory modalities that tends to be overlooked within our very audiovisual culture. And especially, within the realm of art which is so visually identified, we thought it interesting to look at artists who try to well, either critique this kind of overemphasis on visuality and also to provide alternatives to that visuality.

PALCA: And so, how do you present art that incorporates odor?

Mr. DROBNICK: Well, there's two ways. One is to include very fragrant materials and another way is to create synthetic materials that, you know, recent advances in chemistry and synthesis has greatly increased our ability to fabricate smells, ones that exist in nature and ones that don't even exist in nature. So artists have been very keen to adapt this new technology to their own interests, and I guess there's a third way that artists address now, and that is through symbolic means as well. There is a series of videos in the show as well as a smell map that people can participate in. And so with these kinds of representations of smell, one can also consider how language and pictographic markings can also deal with smell.

PALCA: Tell me a little bit more about the smell map. That sounds interesting.

Mr. DROBNICK: Well, it's a piece by Jenny Marketou, and it's the third or fourth one that she's produced. She's done them in Spain, in Europe, and elsewhere. And she kind of looks up to tradition of smell maps which go back to the 18th century, and smell maps were created during that time in order to identify noxious smells. And this is part of the great sanitization campaign that developed into, you know, cities with grand boulevards, septic systems, and sewers and so on, but her map has a kind of different emphasis.

Instead of identifying bad odors or foul fragrances, she tries to encourage and invite the audience to identify smells of all different types such as flowering trees, bakeries, or pizzerias, construction sites and the kind of dustiness that occurs in those kinds of places. So it's really an attempt to increase people's attentiveness to the sense of smell in the city.

PALCA: Right. Well, and just finally, you know, it's too bad we caught you on this last day. Is there any chance that this exhibit will travel?

Mr. DROBNICK: Well, you know, smell works tend to be quite performative and ephemeral and also site-specific. So a piece like Jenny Marketou's smell map took an incredible amount of energy and time by the artist to situate it within the specific environs of Philadelphia. So well, there's a hope. There's a chance. There is nothing in the works right now but we're working on it.

PALCA: All right. Well, we'll stay tuned. Thanks so much for joining us today.

Mr. DROBNICK: Thank you.

PALCA: Jim Drobnick is co-curator of the Odor Limits exhibition running through tomorrow at the Esther M. Klein Gallery at the Science Center in Philadelphia. We're also talking this hour with Avery Gilbert. He's the author of "What the Nose Knows: The Science of Scent in Everyday Life." And we've got a lot of calls, so let's go to the phones and take a call from Daniel in Baltimore, Maryland. Welcome to Science Friday.

DANIEL (Caller): Yes, thank you. Good afternoon. I've got a question I've always wanted to ask someone who might know. My 90-year-old dad, when he went back to the school in his 30s, he shared with me something he tried when cramming for an exam which was to slice open a lemon and sniff that while he was studying and then bring the slice of lemon to the exam, and try to trigger that mnemonic.

PALCA: Interesting. Yeah, mnemonic. That's cool. Let me ask Avery Gilbert about that.

Dr. GILBERT: Yeah, it's a very reasonable idea, in fact. He sort of hacked in his own way to the psychological insight, it's called a sight specific learning, you can see it in rats, you can see it in kids and adults where things you learn in a specific room for example, you can remember better in that room than in a different room later on. So, put the smell up and then recreate the smell, and you're more likely to, it's reasonable to think that you're more likely to recall the key information.

PALCA: Cool. Now, we have a question for Second Life from someone named Chuck, Chuck Beatty (ph). Are there perfumes that use multiple human pheromones? And maybe, before you answer that question, I should get you to tell me if there is a difference between a pheromone and an odor of something that you, you know, are they the same thing?

Dr. GILBERT: Pheromones and odors, that's a vexed question that's just now kind of being untangled. The idea of the pheromone is that it's a chemical substance that will cause behavioral effect in animals and insects. We think of it as mating pheromones for example, and the effects are very specific and rigid and automated. Whether pheromone effects even exist in primates, much less in humans it's kind of kicked back and forth. Martha McClintock of the University of Chicago thinks that pheromones are kind of a classy behavior that influences sort of at the edges of awareness and at the margins, but it's not going to be a dramatic effect.

PALCA: All right. Interesting. Let's talk a call now from Connor in Somerville, Massachusetts. Connor, welcome to Science Friday.

CONNOR (Caller): Hi. Thanks for having me on the show.

PALCA: You bet.

CONNOR: I haven't heard the whole thing so I hope I'm not repeating question. But, I have two questions. One, there's a phenomenon I've experienced and others have, you know, where a very particular smell will trigger extremely vivid memories, and you'll be able to know exactly what the memory was if it's the exact smell you've smelled sometime before. And I never experienced quite the same effect with either any of the other senses, vision, taste, tactile, nothing else. And I was wondering if you guest could speak for that phenomenon.

And then, my second question is with the way that humans have a sensitivity to a certain spectrum of light that we call the visible range and other animals could see more to infrared and honeybees and some birds can see more to ultraviolet. Is there a similar spectrum when it comes to smell? And are there, you know, smells that we just as humans can never smell but other species can?

PALCA: Cool. Those are two really good questions, Connor. The first one, smell and memory.

Dr. GILBERT: That's a very common experience, and that it's this kind of instant and highly vivid evocation of the past. It's something that is unique and it's appealing to smell because you know, in other modalities when we remember the past, we were learning something typically. So, in grade school we were learning something typically. So, in grade school, we learned the names of the state capitals and in adulthood, it's not remarkable to know the capital of North Dakota might be. Joe is shaking his head, I can't remember it either at the moment, but we made an effort to learn it once and so it's so not remarkable when it comes back to us.

Now, with smell, smell is kind of always covering its tracks, in a way. We don't make a conscious effort to remember every smell as we pass through it, and yet it can kind of leave a trail, procedural memories is what psychologists call it. It's kind of imprints itself on a series of events and then we come across it years later, just reawakens that whole sequence in a very vivid way, often misattributed to Marcel Proust the novelist, but as I pointed out in the book, he probably got it wrong and there's a lot of very good authors that captured the spirit of it much better.

PALCA: And what about - oh Bismarck, North Dakota?

(Soundbite of laughter)

PALCA: What about the other point of certain smells that are just beyond our ability but maybe some other species can capture?

Dr. GILBERT: That's probably true. In many ways, the natural smells in the world the volatile smells aren't there for us. Therefore, insects talking to insects, plants talking to insects and vice versa and we're just eavesdropping on these interspecies conversations that go on. One of the interesting outcomes of the new work on the genetics of odor reception is that we can see how similar our receptors are to those of mice, say, or apes or rabbits and so forth.

As it turns out, with chimpanzees, that kind of families of odor receptors that we have are very closely mapped on to chimpanzee ones. But even with mice, what the kind of groupings and here's a little speculation because we haven't nailed down a particular smell to a particular receptor, but it's very likely that what we're smelling in the world, in written large is what a mouse is smelling in the world and vice versa.

PALCA: Now, it's been suggested that certain smells are somewhat iconic for certain things, and we have some lavender there that came from someone's garden?

Dr. GILBERT: It's great. It's very fresh.

PALCA: It's a nice smell, but somehow, it seems to be associated to spinsterhood?

Dr. GILBERT: In this country, it is. Lavender's one of the favorite ingredients for aroma therapists around the world and it's a popular smell. It has a connotation of calmness and calming when aroma therapists talk about it, and it's used in a lot of products in Europe with that kind of a positioning. In this country, we tend to think of it as old ladies and grandma's closet sort of, it's not an exciting smell.

PALCA: It seems to me - I was at a field in France once where there was just rows and rows of...

Dr. GILBERT: It's still grown there, absolutely.

PALCA: Yeah. Interesting. All right, let's take another call now and go to Vincent in Long Island, New York. Welcome to the show, Vincent.

VINCENT (Caller): Thank you. How are you guys today?

PALCA: Good.

VINCENT: Good. I have a question in regards to why is it that when humans smell certain obnoxious odors that it makes us nauseous or it's making us want to be very sick? Whereas dogs who also have a strong sense of smell doesn't seem to be affected by odor in a way like that?

PALCA: Good question, Vincent. Thanks.

Dr. GILBERT: Yeah, excellent. I think it's because we attribute meanings to smells and that dogs have sort to have taking them at face value in a way. The smell of the dog is just a fact out in the world but doesn't have a value to it, and we start thinking about, oh, that's a smell of a horrible you know, blood and guts in a car accident or a slaughter house or something. We start thinking about the implications of that. I think that helps bring up the nausea in a way.

PALCA: Interesting. We're talking with Avery Gilbert. He's the author of "What the Nose Knows: The Science of Scent of in Everyday Life." I'm Joe Palca and this is Talk of the Nation from NPR News. I guess we have to bring up one other question, two parts of the same question. I know I'm asking for trouble here, but men and women, different ability to smell?

Dr. GILBERT: Yeah, that's one of the issues where conventional wisdom is actually correct. Women claim to be able to smell better and be more sensitive, and we have to give them that. On an average, a woman can smell, detect an odor at a lower concentration in the air, and women are generally able to identify them more readily, more quickly which goes with the female advantage and verbal ability over us guys.

PALCA: But now, let's flip it around and so, women in terms of how they smell. That's a section in the book that I can't let go. This is the difference between male and female farts. You say, it's been scientifically shown that volume, ounce for ounce, women have smellier farts than men.

Dr. GILBERT: That's true. There's a research group using gas chromatography as you mentioned. Very cool technique and it's only been put to these age-old questions, has been argued for centuries, guys had been insisting that women are stinkier ounce for ounce, and they're correct. The offsetting fact, though, is that guys produce more gas, and so, I think it's a draw in the end, so to speak.

PALCA: See, I told you, Annette, we were going to get to that. Annette didn't put that down as one of the questions, but she's the producer, I get to ask the questions. And let's go to another caller now and take, is it Carthic (ph) from Apex, North Carolina.

CARTHIC (Caller): It is Carthic from Apex, North Carolina.

PALCA: Welcome. Welcome to the show.

CARTHIC: Thank you. Thank you for taking my call.

PALCA: You bet.

CARTHIC: I just had a quick question about the comment that there's an array of say a thousand of chemicals that trigger smell responses. Are there individual receptors for each one of these or is there a signature of interactions that each chemical trigger that then is read as a particular (unintelligible) by our brain?

PALCA: Interesting. Very interesting. What about that? Do we have a receptor for one (unintelligible) all or something or they get mixed up somehow?

Dr. GILBERT: That's a great question. Actually, there's a PhD to be pursued there if you want to. It's a really hot topic right now. It seems as if a given chemical will probably stimulate two to three or four more receptors to a greater or lesser degree. And just figuring out how they overlap with each other in the receptor fields, again, talking metaphorically, is of great interest in the neuroscience community now because that will help us figure the psychological code for how smells are transferred again from a chemical structure into a psychological coding and an experience.

PALCA: So, what's the worst thing you've ever smelled?

Dr. GILBERT: I'm not a fan of vomit in any form. I can do the diaper-cleaning routine, but the vomit gets me.

PALCA: There's one that I remember. Maybe, somebody, I worked in a lab, a biochemical lab for a while and there was this chemical that was used for staining DNA or something called Beta-Mercaptoethanol, BME, and I mean, they open a vial of that anywhere in the building and it was like run for your life. It's got sulfur in it. Sulfur seems to be at the root of a lot of not-so-nice smells.

Dr. GILBERT: Right. I mean, that's your basic fart ingredient. There's a lot of sulfur containing Mercaptant smells. I mean, that Mercaptants are, the mixture of them uses a warning signal in natural gas for example. Yeah, they're often the culprits.

PALCA: All right. Well, I'm afraid that's where we're going to have to leave it, very interesting discussion. I hope everybody has learned that smell is something that smell is we both pay attention to, admire, use when we need to, and appreciate for all the complexities that it has. Thanks for joining us, Avery.

Dr. GILBERT: My pleasure.

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