why is it that when you peel and cut an onion, your eyes get panful?

Answer 1

When you cut into it, you release a gaseous sulfur-containing chemical called the lachrymatory factor (propanthial S-oxide) that spreads in the air and comes into contact with your eyes.
The lachrymatory factor from an onion activates the nerve endings of pain fibers in the top layer of the cornea, leading to increased production and release of tears.

Answer 2

As any chef knows, cooking an onion produces a very strong aroma that most people enjoy. But cutting up an onion stings your eyes and makes you tear up uncontrollably. If you love to include onions in your dishes, you're probably frustrated by this all the time. So just what is it in onions that make them such an ordeal to prepare?
When you slice through an onion, you break open a number of onion cells. Some of these cells have enzymes inside of them, and when they are sliced open, the enzymes escape. The enzymes then decompose some of the other substances that have escaped from sliced cells. Some of these substances, amino acid sulfoxides, form sulfenic acids, which then quickly rearrange themselves into a volatile gas.

The gas reaches your eyes and reacts with the water that keeps them moist. This changes the chemical's form again, producing, among other things, a mild sulphuric acid, which irritates the eyes. The nerve endings in your eyes are very sensitive and so they pick up on this irritation (this is why our eyes sting when we slice onions). The brain reacts by telling your tear ducts to produce more water, to dilute the irritating acid so the eyes are protected. Your other reaction is probably to rub your eyes, but this will actually make the irritation a lot worse, of course, if you have onion juices all over your hands.

Answer 3

Onions contain the chemical sulfur, as well as enzymes that speed up chemical reactions. The sulfur and the enzymes rest on opposite sides of the onions’ cell walls-until they are cut open. Then the sulfur and enzymes come in contact and start a chain of chemical reactions. New molecules float up in the air and react with the nerve cell membrane of the eye to form sulfuric acid and cause tearing. While you can’t see these reactions, you can feel the results when your eyes start to burn and water.

To prevent tearing, chill onions for about 30 minutes before cutting them. The chemical reaction will be slowed down by the lower temperature. Another strategy to try is cutting the onion with a sharp knife. When you do this, less damage will occur to the onion’s cells and fewer of the tear-producing compounds will be released. Finally, be sure to cut the root end of the onion last, as it contains the largest concentration of the sulfuric compounds. For more information about onions, visit www.onions-usa.org.

Answer 4

I believe it is the sulphur.

But, why just onions ?

For your eyes NOT to tear, rinse peeled onion under cold water for a few seconds; helps a lot.

Answer 5

There is a gas which, when you cut an onion's skin, exudes from it and irritates your eyes. I believe this gas is also the source of onion f***s.

Answer 6

It's one of the chemicals present in the onion. Peel it under water to prevent this.

Answer 7

Gaseous Sulphur compounds are released which irritate the eyes causing them to water (and become pAinful).

Tear gas is a derivative of the same kind of compounds.

Answer 8

its supposed to be caused by a chemical reaction caused when cutting the onion, i prefer to think perhaps you sympathise with the onion..

Answer 9

because the sulphur content in the onion juice combines with the tears to form very weak sulphuric acid which irritates the eyes causeing you to cry :-)

Answer 10

Actually if you don't breath through your nose your eyes will not tear up. It is because you are inhaling the onions scent and it is causing you to cry. Dude, it's not your eyes it is your nose. Try it, I have and it works. Breath through your mouth you will see.