Why Chewing on Foil Hurts Your Teeth

Foil is good to use on food, but you'll get a shock if you bite it.
Foil is good to use on food, but you'll get a shock if you bite it. Maksym Azovtsev, Getty Images

There are two types of people. One group can bite aluminum or tin foil with impunity, suffering nothing worse than a faint metallic taste. The other group gets a painful electric zing from chewing on foil. Why does chewing on foil hurt some people and not others? How does it work? Here's what happens.

Biting Foil Hurts if You Have Dental Work

Got braces, amalgam fillings, or a crown? Chewing on foil will hurt. If your mouth is blissfully free of dental work, you won't feel pain when you chew foil, unless a sharp corner stabs you. That's not the same pain at all, so if you aren't affected by foil, count yourself lucky!

Foil Turns Your Teeth into a Battery

If you don't react to foil, but want to know what you're missing, you can get an identical experience licking both terminals of a battery. Fun, right? It's the same because chewing foil produces a galvanic shock. Here's what happens:

  1. There is a difference in the electric potential between the metal foil (usually aluminum) and the metal in your dental work (usually mercury, gold, or silver). It only happens when there are two different types of metals.
  2. The salt and saliva in your mouth allow current to flow from one metal to the other. Essentially, the fluids in your mouth are an electrolyte.
  3. Electricity travels between the metal foil and the metal in dental work.
  4. The electric shock passes down your tooth to your nervous system.
  5. Your brain interprets the impulse as a painful jolt.

This is an example of the voltaic effect, named for its discoverer, Alessandro Volta. When two dissimilar metals come into contact with each other, electrons pass between them, generating an electric current. The effect can be used to make a voltaic pile. All you need to do to make this simple battery is to stack pieces of metal on top of each other.

Would you like to try another electrochemistry demonstration? You can use an electrochemical reaction to make copper and zinc pennies appear to turn into gold and silver. You won't even get zapped trying it!