Why Is It Painful To Bite Aluminum Foil?

When (dental) metal in your mouth comes in contact with aluminum foil, your teeth get a painful shock from the electricity produced. Christian Sager explains how the voltaic effect plays out in your mouth in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff from how stuff works. Hey, everybody,
it's me Christian Sager. Now today's question is why is
it so painful to bite into aluminum foil? And if
you're from across the pond, you may be wondering right now,
why is he saying aluminium instead of aluminium? Well, I'm American,

(00:23):
That's how I pronounced it all my life. I apologize.
We're gonna go forward with aluminum. But it's a good question, right.
So first things first, it's actually not painful for everybody
to bite into this foil. It's painful for people who
have fillings or crowns made of metal. You probably already
knew that part, So let's fast forward. What is actually

(00:44):
happening here. It's sort of like making a battery. So
how does this happen exactly? Well, first, it's two different metals,
the aluminum foil and the metal in your filling or crown.
They have what's called an electrochemical potential difference, and they
create the sort of voltage in the environment in your mouth,
which is moist and salty. It's produced by your saliva.

(01:07):
It's perfect for these two things to come into contact
this way and to transmit energy. The electrical stimulation from
this bootleg battery you have created is hitting the nerve
in your tooth, and that is producing that weird, unique pain.
The production of this current between the contact of two

(01:27):
dissimilar metals. It's actually a pretty old concept. It's called
the voltaic effect. It's named after a guy named Alessandro Volta,
who most people credit with discovering this. In fact, if
you want to learn more about this, on my other podcast,
Stuff to Blow Your Mind, we went really far into
voltaic batteries in an episode we did on Frankenstein. Now

(01:50):
Volta he was making extra batteries a long time ago,
and what he did was he stacked these dissimilar metals
together and in between them he would put water her
paper soaked with salt water. And he found that by
doing this he could create a very low power battery.
So that's essentially it. That's what's happening when you open

(02:11):
a candy bar and you bite down on a piece
of chocolate that still has a little bit of foil
in it and you freak out because it's painful. You're
essentially creating a battery in your mouth. Check out the
Brainstuff channel on YouTube, and for more on this and
thousands of other topics, visit how stuff works dot com.