MARCO TIZZANO: A lot of people enjoy stuff that is painful.
So I was one of these persons that say, oh, I
eat always chili pepper.
I can eat more and more and get accustomed to that.
And get to the next step, and get always hotter chili.
In reality, it's not so simple.
Most of the time, you're, it's hot.
And then you take another one and say, it will be less.
And it's is even more.
It's not that more you eat, less you perceive that.
LUKE GROSKIN: Marco Tizzano was an investigator at the Monell
Chemical Senses Center, whose interest in the science
of spicy didn't begin in a lab.
MARCO TIZZANO: Nights and weekends, I
was working as a chef.
And I was fascinated by the idea of the other type
of perception, of sensory perception, how they work.
And that is how I started my adventure in science.
LUKE GROSKIN: And while Dr. Tizzano
can cook many delicious dishes, his research has little
to do with taste and smell.
Instead, his focus is on chemesthesis
MARCO TIZZANO: Chemesthesis is practically the science,
the study, the perception of the pain transmitted
by the trigeminal nerve.
LUKE GROSKIN: Which branches out from a central ganglion
in your head down throughout your nose, mouth, and eyes.
MARCO TIZZANO: And so all these processes
will just transmit the sensation from this periphery part
to the central ganglion, and give you
a sensation pain, or cold, or warm,
depending on what you are using as stimuli.
LUKE GROSKIN: In the case of chili peppers,
that stimuli is a molecule known as capsaicin,
which causes a burning sensation,
amongst other maladies.
How does one molecule achieve such a lasting effect?
MARCO TIZZANO: Capsaicin is a molecule
that will bind specifically to a class of receptor that
are called TRPV.
And they are in mucosas like the mouth, the nose, the eyes.
So imagine capsaicin like a key, and the receptor TRPV
like a door.
When the capsaicin would bind to the door,
will open the receptor.
And the receptor will allow ion to run through it.
This change of potential would be
transmitted through the nerve to the center of the system,
to the brain.
And that is where you get the pain sensation of the heat.
But then locally, there is this [INAUDIBLE] neurotransmitter
that is called Substance P and CGRP.
And those are the one that would cause
you the swelling, the pain, and other sensations.
But then there is also fibers in the nose.
You will activate there a local inflammation.
And that is why you have a runny nose or sneezing.
And because the same nerve is also stimulating the eyes,
then you will have your watering eyes.
LUKE GROSKIN: And because the whole reaction
is meant to protect you from what your body has
deemed unhealthy, there are a few methods
to stop the process.
You can't drink water because--
MARCO TIZZANO: The sensation will come back again
because capsaicin is still stuck on the receptor.
Another way is to drink something
that contains fat like milk, or something that contain alcohol
like beer, because the alcohol and fat in the milk
will actually move that from the receptor.
LUKE GROSKIN: So what if you expose the system over and over
again.
Can you actually desensitize it?
MARCO TIZZANO: There is all these studies
that demonstrate that very short presentation of a capsaicin
molecule in very short time frames
with cause you to sensitize the receptor.
Perception of that would be stronger and stronger
and stronger until you stop because you cannot bear that
anymore.
LUKE GROSKIN: The pain does diminish eventually,
but that's not because you gained
a tolerance to the chemical.
MARCO TIZZANO: What that means is that the receptor will not
desensitize, but it will internalize
inside the membrane of the fibers
because you want to protect the nerve from getting damaged.
LUKE GROSKIN: If the pain does seem
to go away in the long term, you might actually
be damaging your nerves.
MARCO TIZZANO: If there is somebody more
sensitive to that, may damage that system.
And also, sometimes you cannot come back from that and you
will lose that system.
LUKE GROSKIN: And if all this doesn't convince you
that you can't just build tolerance to spicy food,
just remember, it's all in your head anyway.
MARCO TIZZANO: There are several studies
that demonstrate that if you eat hot pepper
or if you're a person that don't eat hot pepper
and you provide them different concentration of chili pepper,
both of them will describe with no statistical difference
that these chili pepper were unbearable, or mild,
or very bland.
And that is because the people that eat the hot pepper still
perceive that as a pain, but they enjoy it.
They eat that and say, oh, I can do that.
But it's just because you want to do that.
But it's very painful anyway.
LUKE GROSKIN: For Science Friday, I'm Luke Groskin.