Transcript generated automatically by AI and may contain errors.
Chapter 1: What is the main topic discussed in this episode?
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This BBC podcast is supported by ads outside the UK. Hello, welcome to Doctor's Notes.
I'm Dr. Chris Van Telleken. As always, I'm here with my identical twin brother. As always, I'm here, Dr. Zart.
Chapter 2: What causes body odour and why does it vary?
We've just finished recording our interview with Matthew Cobb, Professor Emeritus of Zoology at the University of Manchester on the topic of body odour. In the main episode, we looked at what causes body odour and why it varies so much from person to person. That's right, Zand. We looked at what body odour can and can't tell us about our health and each other.
We did some myth-busting about all that stuff. And that, for me, was another pile of stuff I'm not going to worry about anymore. Well, Matthew was kind enough to stay on for Doctor's Notes. And we wanted to find out about his extraordinary scientific career, how it got started. And we wanted to know about our sense of smell.
how it compares to other animals, what happens when we lose our sense of smell. And how the way that humans experience smells might have affected our evolution. How we smell animals, how they smell us, and how we smell each other. But Chris, before we get into all that, I wanted to talk a little bit about deodorants because we have some questions from a listener called Joey.
He said, I'd be grateful for an episode on deodorant. What is the best type? Is there a best spray, roll-on, stick, ball, aerosol? There's a little paste that you come out of a tube with a spatula. I've got some of that. It's quite good, actually. I had one that was a crystal. It was like a piece of, like a magical, like the deodorant that Merlin would use. Like the Knights of the Round Table.
It was like more of a salt thing. I think it was the aluminium salt. I think it was the raw crystal version of what is in the other deodorants, I believe. Well, the other thing is, with the rise in cancers in people in general, and particularly young people, is any of this associated with the chemicals in deodorant? Strong enough chemicals to stop a human smelling? Are they doing us harm as well?
Why do some people get worse body odour than others? Can they do anything about it? Joey, these are brilliant questions. We're going to put some of these questions to our expert. But a couple of the questions are quite important health questions. So I think, Chris, you and I should address them. The first one is how do deodorants actually work? We casually use the term deodorant.
In fact, a deodorant just means a thing that masks the smell. So that's the sort of aroma bit of it. But the antiperspirant is the thing that really stops your body odor. And the way it does it is typically it's using an aluminium salt, a chemical like aluminium zirconium or aluminium chlorhydrate. And when these... These salts dissolve in the sweat of your armpits.
They form a sort of gel that plugs your sweat gland and they literally stop the sweat coming out of the sweat gland. And that means there's less sweat for the bugs to digest and produce sweat. So that's how the deodorant works.
And so there is some evidence that if you want maximum protection from smelling, you should apply your antiperspirant at night when you generally have slightly lower sweat production. So the aluminium salts enter the sweat ducts, form plugs. Before they get washed away by sweating.
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Chapter 3: How does our sense of smell compare to that of other animals?
Am I right, Matthew, we don't have a machine... that measures smell. I know we have things like gas chromatographs and things, but more or less, essentially, if you want to measure if something smells, you've got to get a human nose on it, basically.
Yeah, I mean, that's basically right. But of course, you know, your noses, are you identical?
We are identical. Yeah, we are.
Okay, so pretty much your sense of smell in terms of your genetic basis, your sense of smell should be pretty much identical. However, you've now been living for however long, so...
one there may have been mutations that have accumulated between you but secondly you've also had slightly different life experiences so that will also affect your sense of smell so you say get a human to smell well that's easier said than done because one human is not the same as another identical twins should have a very very similar sense of smell but it won't be absolutely identical like other things about you aren't absolutely identical yeah
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Chapter 4: What role does DNA play in our experience of smell?
Can you talk about how we perceive a smell as good or bad?
Well, I can give you a very vague answer, but then I can show you why it is vague. So we've got around about 400 genes that encode the receptor, that is the lock, that detects the smell. But we can actually detect far more than 400 smells because each receptor can detect more than one kind of smell. And each smell can activate more than one kind of receptor.
OK, so it's incredibly complicated right from the very beginning. So when you're doing your smelling, it's through your nose. It's right at the level of your eye. You've got dangling down through the base of your skull, your receptor neurons. And so that's where the action takes place, right up here.
If a listener were to point between their eyes, backwards through their brain, sort of behind their eyes at that level, that's where those receptors are.
That's where it's going on. Right, and despite what you may think, you are not detecting odours, chemicals in the air. Oh. Right, so just remember, basically you're a fish, okay? Humans, we come ultimately from the sea, and if we've got neuron cells... in contact with the air, they just shrivel up and die.
So our neurons are in fact bathing in a layer of mucus, and so the smells that we detect have to go through that layer of mucus. And even there, things happen. There are certain odours, for example, that we cannot detect because they are chopped up, metabolised in that layer of mucus.
And then they have to be taken by what are nicely called molecular chaperones, which actually protect the smells from being degraded by this layer of mucus. And then the enzymes that are in there and then they're kind of delivered to the receptor. You were going to give us a vague answer and now you're like, well, molecular chaperone. Well, that's just saying how it gets in there.
It's not talking about what you're interested in is valence, this meaning. There is a substance called androstenone, which is an odour that the male pig produce. And it happens to only activate one of our receptors out of the 400 or so.
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Chapter 5: What happens when we lose our sense of smell?
Just one detects this. And we know that there are... Tiny differences, single letters of DNA that alter our perception from some people thinks it smells disgusting, like going down a back alley where men have been peeing, absolutely revolting. Other people like me think it smells quite sweet. Others can't detect it at all. And some people, although they generally don't admit it, going...
hey, how are you doing? They find it really quite exciting.
So, Matthew, we have, knowing that you were coming on, I went on the internet and bought some of this. Now, I think this is a product that's used, am I right, by pig farmers. It is actually somewhat useful. I believe it is also marketed... for sort of men to make themselves appealing.
It's a sex pheromone, allegedly, attracts men fast, attracts women fast. So depending on what exactly you've got, what have you got there?
I mean, when you go shopping on the internet for pig sex hormones, I've got a slightly sort of rainbow foil package. I'll hold it up so that you can see it in the camera. So I don't, this doesn't look like it's being sold for agricultural use. I think this is probably not.
They sell that in a can. You spray it up the female pig's nose, and then you surprise her with a turkey baster, and you get piglets.
Okay. Well, this is not the ambition.
We've got five people in the room. So the reactions are... Well, let's see their reactions. Okay, here we go. There are differences between different groups.
Right, I'll do it as if I'm at the perfume shop, you know, where they spray it on the little piece of paper. Here we go. Right, Chris. Now, what do you think, Chris? I think we have bought a recreational perfume, and that is just perfume, isn't it? It just smells like a magazine.
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Chapter 6: How do deodorants and antiperspirants actually work?
Not a pig's bum. It just smells like men.
Smells like men? Really? You do think it smells like men's mask? If you went out with someone... You wouldn't put it on yourself? You think this would be like a man thing to wear? But if I was wearing this, would you think Chris is smelling manly today? Well, Joe did a sort of... What I can only describe as a shimmy. Andres, can you have a whiff as well? We've got our sound engineer, Andres.
Here we go. Andres is getting what we're getting, cheap perfume. Cheap perfume, air freshener, that kind of thing. I was worried that I'd been ripped off on the internet, which has happened to me before. Well, that's so exciting, isn't it? We must go to a pig farm immediately.
Well, I suppose there's this odd thing where two of the people in the room say that this would be a nice manly smell to wear and it would be quite attractive. Yeah.
So what we haven't got is somebody who thinks, that's disgusting, I don't want to go near that, right? So, I mean, if you get enough people, that's what you end up with. And the problem here we got is so we know that you've all smelt the same thing. You have basically the same receptor. There's just one molecule that is detecting this odour. And there are these tiny differences between us.
And that is... in some mysterious way that change in the shape of the lock is altering the way that the neuron responds and that different response that's our perception so you've actually gone not just from why do things smell nice or nasty to actually getting to one of the most profound problems of philosophy and science that is what is consciousness what is perception because between us
There are differences in the way our neurons are firing. One class of neuron is firing and that produces this different sensation. I love that.
I love that you've gone from the internet marketing of sort of attracting the opposite sex with pig sex hormones to the, you know, the deep questions of consciousness and perception. Matthew, can we do a bit more on smell biology? Humans famously have a very bad sense of smell. Is that true? How do we compare to other mammals?
It's very difficult to tell. I mean, one of the ways you can look at it is how many kinds of receptors do we have? And as I said, we've got around 400. The elephant has the largest repertoire that's known, 1,200. A dog, which is famously pretty good at smelling, or we think it is compared to us, would have around about 600.
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Chapter 7: Is there a connection between deodorants and health concerns?
And part of the problem of studying mating behaviour, although it's incredibly significant in the life of an animal, is that... The flies often wouldn't be in the mood.
You'd get them all ready, get the male and the female, put them together, and they'd just sit on either side of the little cell that I was studying, and they'd say, no, not today, Josephine, I'm not interested, and nothing much would happen. And the person I was working with, we were thinking, partly, to be absolutely honest...
getting a job, getting a research post with the French CNRS research organisation. I needed a project. And at the time, this is in the late 1980s, olfaction was very much underdeveloped. Not many groups were studying it. And exactly how it worked, the molecular basis of the receptors was largely unknown.
And my boss said, look, you should start thinking rather than doing something on mating, what about olfaction? thinking about olfaction, because that's something that would, you know, perhaps generalise across humans and all animals. And he said, you know, you should think about using maggots. And I said, I don't want to study maggots. They're really boring, right? They don't do anything.
And that shows you quite how wrong I was, because he nagged and nagged and said, look, just do one experiment. So I looked up in the literature how you'd study a sense of smell. Maggot, you get a what's called a Petri dish, which is a small dish with some jelly at the bottom of it, hard jelly.
You get a load of maggots, you put them in the middle, you put a smell on one side and you put the lid on. And to my amazement, I put a smell kind of like a pear droppy smell one side and And all of the maggots just charge towards it. They've been like a hungry caterpillar. All they want to do is eat. So they're really interested in smell.
So me saying they're boring was actually the reason to study them. A maggot just wants to turn into a fly. It just wants to eat and get big. It's got a nose that is composed of only 21 neurons, not millions as in a human nose. And because you can fool around with its genetics, you can make a maggot that has just one smell cell that works.
So you could then record from that cell and see how it responded to different odours and try to understand how smell is processed at the very earliest stages before you even get into the brain. So that's how I ended up getting into it.
It's a lovely description of the scientific process. There's a bit of pragmatic, like you've got to do something. You've got to do a job. If you want to be a scientist, you better do some science. And then the thrill of an experiment that works then catalyzes your whole career, I guess.
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