The smelly mystery of the human pheromone

Do our smells make us sexy? Popular science suggests yes — pheromones send chemical signals about sex and attraction from our armpits to potential mates. But, despite what you might have heard, there is no conclusive research confirming that humans have these smell molecules. In this eye-opening talk, zoologist Tristram Wyatt explains the fundamental flaws in current pheromone research, and shares his hope for a future that unlocks the fascinating, potentially life-saving knowledge tied up in our scent.

"Pheromone" is a very powerful word.

It conjures up sex, abandon, loss of control,

and you can see, it's very important as a word.

But it's only 50 years old. It was invented in 1959.

Now, if you put that word into the web,

as you may have done,

you'll come up with millions of hits,

and almost all of those sites are trying to sell you

something to make you irresistible

for 10 dollars or more.

Now, this is a very attractive idea,

and the molecules they mention

sound really science-y.

They've got lots of syllables.

It's things like androstenol, androstenone

or androstadienone.

It gets better and better,

and when you combine that with white lab coats,

you must imagine that there is

fantastic science behind this.

But sadly, these are fraudulent claims

supported by dodgy science.

The problem is that, although there are many

good scientists working on what they think

are human pheromones,

and they're publishing in respectable journals,

at the basis of this,

despite very sophisticated experiments,

there really is no good science behind it,

because it's based on a problem,

which is nobody has systematically gone through

all the odors that humans produce --

and there are thousands of
molecules that we give off.

We're mammals. We produce a lot of smell.

Nobody has gone through systematically

to work out which molecules really are pheromones.

They've just plucked a few,

and all these experiments are based on those,

but there's no good evidence at all.

Now, that's not to say

that smell is not important to people.

It is, and some people are real enthusiasts,

and one of these was Napoleon.

And famously, you may remember

that out on the campaign trail for war,

he wrote to his lover, Empress Josephine,

saying, "Don't wash. I'm coming home."

(Laughter)

So he didn't want to lose any of her richness

in the days before he'd get home,

and it is still, you'll find websites

that offer this as a major quirk.

At the same time, though,

we spend about as much money

taking the smells off us

as putting them back on in perfumes,

and perfumes are a multi-billion-dollar business.

So what I want to do in the rest of this talk

is tell you about what pheromones really are,

tell you why I think we would expect

humans to have pheromones,

tell you about some of the
confusions in pheromones,

and then finally, I want to end with

a promising avenue which shows us

the way we ought to be going.

So the ancient Greeks knew

that dogs sent invisible signals between each other.

A female dog in heat

sent an invisible signal to male dogs

for miles around,

and it wasn't a sound, it was a smell.

You could take the smell from the female dog,

and the dogs would chase the cloth.

But the problem for everybody

who could see this effect

was that you couldn't identify the molecules.

You couldn't demonstrate it was chemical.

The reason for that, of course,

is that each of these animals

produces tiny quantities,

and in the case of the dog,

males dogs can smell it, but we can't smell it.

And it was only in 1959 that a German team,

after spending 20 years in
search of these molecules,

discovered, identified, the first pheromone,

and this was the sex pheromone of a silk moth.

Now, this was an inspired choice
by Adolf Butenandt and his team,

because he needed half a million moths

to get enough material to do the chemical analysis.

But he created the model

for how you should go about pheromone analysis.

He basically went through systematically,

showing that only the molecule in question

was the one that stimulated the males,

not all the others.

He analyzed it very carefully.

He synthesized the molecule,

and then tried the synthesized
molecule on the males

and got them to respond and showed it was,

indeed, that molecule.

That's closing the circle.

That's the thing which has
never been done with humans:

nothing systematic, no real demonstration.

With that new concept,

we needed a new word,

and that was the word "pheromone,"

and it's basically transferred excitement,

transferred between individuals,

and since 1959, pheromones have been found

right the way across the animal kingdom,

in male animals, in female animals.

It works just as well underwater

for goldfish and lobsters.

And almost every mammal you can think of

has had a pheromone identified,

and of course, an enormous number of insects.

So we know that pheromones exist

right the way across the animal kingdom.

What about humans?

Well, the first thing, of course,

is that we're mammals,

and mammals are smelly.

As any dog owner can tell you,

we smell, they smell.

But the real reason we might think

that humans have pheromones

is the change that occurs as we grow up.

The smell of a room of teenagers

is quite different

from the smell of a room of small children.

What's changed? And of course, it's puberty.

Along with the pubic hair

and the hair in the armpits,

new glands start to secrete in those places,

and that's what's making the change in smell.

If we were any other kind of mammal,

or any other kind of animal,

we would say,

"That must be something to do with pheromones,"

and we'd start looking properly.

But there are some problems, and this is why,

I think, people have not looked for

pheromones so effectively in humans.

There are, indeed, problems.

And the first of these

is perhaps surprising.

It's all about culture.

Now moths don't learn a lot

about what is good to smell, but humans do,

and up to the age of about four,

any smell, no matter how rancid,

is simply interesting.

And I understand that the major role of parents

is to stop kids putting their fingers in poo,

because it's always something nice to smell.

But gradually we learn what's not good,

and one of the things we learn

at the same time as what is not good

is what is good.

Now, the cheese behind me

is a British, if not an English, delicacy.

It's ripe blue Stilton.

Liking it is incomprehensible to
people from other countries.

Every culture has its own special food

and national delicacy.

If you were to come from Iceland,

your national dish

is deep rotted shark.

Now, all of these things are acquired tastes,

but they form almost a badge of identity.

You're part of the in-group.

The second thing is the sense of smell.

Each of us has a unique odor world,

in the sense that what we smell,

we each smell a completely different world.

Now, smell was the hardest

of the senses to crack,

and the Nobel Prize awarded to

Richard Axel and Linda Buck

was only awarded in 2004

for their discovery of how smell works.

It's really hard,

but in essence, nerves from the brain

go up into the nose

and on these nerves exposed in the nose

to the outside air are receptors,

and odor molecules coming in on a sniff

interact with these receptors,

and if they bond, they send the nerve a signal

which goes back into the brain.

We don't just have one kind of receptor.

If you're a human, you have about 400

different kinds of receptors,

and the brain knows what you're smelling

because of the combination of receptors

and nerve cells that they trigger,

sending messages up to the brain

in a combinatorial fashion.

But it's a bit more complicated,

because each of those 400

comes in various variants,

and depending which variant you have,

you might smell coriander, or cilantro, that herb,

either as something delicious and savory

or something like soap.

So we each have an individual world of smell,

and that complicates anything

when we're studying smell.

Well, we really ought to talk about armpits,

and I have to say that I do
have particularly good ones.

Now, I'm not going to share them with you,

but this is the place that most people

have looked for pheromones.

There is one good reason,

which is, the great apes have armpits

as their unique characteristic.

The other primates have scent glands

in other parts of the body.

The great apes have these armpits

full of secretory glands

producing smells all the time,

enormous numbers of molecules.

When they're secreted from the glands,

the molecules are odorless.

They have no smell at all,

and it's only the wonderful bacteria

growing on the rainforest of hair

that actually produces the smells

that we know and love.

And so incidentally, if you want to reduce

the amount of smell,

clear-cutting your armpits

is a very effective way of reducing

the habitat for bacteria,

and you'll find they remain less smelly

for much longer.

But although we've focused on armpits,

I think it's partly because they're the least

embarrassing place to go and ask people for samples.

There is actually another reason why we might not

be looking for a universal sex pheromone there,

and that's because 20 percent
of the world's population

doesn't have smelly armpits like me.

And these are people from China, Japan,

Korea, and other parts of northeast Asia.

They simply don't secrete those odorless precursors

that the bacteria love to use to produce the smells

that in an ethnocentric way we always thought of

as characteristic of armpits.

So it doesn't apply to 20 percent of the world.

So what should we be doing

in our search for human pheromones?

I'm fairly convinced that we do have them.

We're mammals, like everybody else

who's a mammal, and we probably do have them.

But what I think we should do

is go right back to the beginning,

and basically look all over the body.

No matter how embarrassing,

we need to search and go for the first time

where no one else has dared tread.

It's going to be difficult,

it's going to be embarrassing, but we need to look.

We also need to go back to the ideas

that Butenandt used when he
was studying the silk moth.

We need to go back and look systematically

at all the molecules that are being produced,

and work out which ones are really involved.

It isn't good enough simply to pluck a couple

and say, "They'll do."

We have to actually demonstrate

that they really have the effects we claim.

There is one team that I'm
actually very impressed by.

They're in France, and their previous success

was identifying the rabbit mammary pheromone.

They've turned their attention now

to human babies and mothers.

So this is a baby having a drink of milk

from its mother's breast.

Her nipple is completely hidden

by the baby's head,

but what you'll notice is a white droplet

with an arrow pointing to it,

and that's the secretion from the areolar glands.

Now, we all have them, men and women,

and these are the little bumps around the nipple,

and if you're a lactating woman,

these start to secrete.

It's a very interesting secretion.

What Benoist Schaal and his team developed

was a simple test to investigate

what the effect of this secretion might be,

in effect, a simple bioassay.

So this is a sleeping baby,

and under its nose, we've put a clean glass rod.

The baby remains sleeping,

showing no interest at all.

But if we go to any mother

who is secreting from the areolar glands,

so it's not about recognition,

it can be from any mother,

if we take the secretion

and now put it under the baby's nose,

we get a very different reaction.

It's a connoisseur's reaction of delight,

and it opens its mouth

and sticks out its tongue

and starts to suck.

Now, since this is from any mother,

it could really be a pheromone.

It's not about individual recognition.

Any mother will do.

Now, why is this important,

apart from being simply very interesting?

It's because women vary

in the number of areolar glands that they have,

and there is a correlation between the ease

with which babies start to suckle

and the number of areolar glands she has.

It appears that the more secretions she's got,

the more likely the baby is to suckle quickly.

If you're a mammal,

the most dangerous time in life

is the first few hours after birth.

You have to get that first drink of milk,

and if you don't get it, you won't survive.

You'll be dead.

Since many babies actually find it difficult

to take that first meal,

because they're not getting the right stimulus,

if we could identify what that molecule was,

and the French team are being very cautious,

but if we could identify the molecule,

synthesize it, it would then mean

premature babies would be more likely to suckle,

and every baby would have a better chance

of survival.

So what I want to argue is this is one example

of where a systematic, really scientific approach

can actually bring you a real understanding

of pheromones.

There could be all sorts of medical interventions.

There could be all sorts of things

that humans are doing with pheromones

that we simply don't know at the moment.

What we need to remember is pheromones

are not just about sex.

They're about all sorts of things to do

with a mammal's life.

So do go forward and do search for more.

There's lots to find.

Thank you very much.

(Applause)