Onions & teary eyes

[Hosay]

Hi
Is it true that if you chew gum while cutting onions you won’t cry?
If so, why does chewing gum stops it from making you tear?

Thank You

[Squink]

Cutting an onion releases enzymes which produce the irritating gas syn-propanethial-S-oxide:

The formation of syn-propanethial-S-oxide peaks at about 30 seconds after mechanical damage to the onion and completes its cycle of chemical evolution over about five minutes.

"Its effects on the eye are all too familiar. The front surface of the eye–the cornea–serves several purposes, among them protection against physical and chemical irritants. The cornea is densely populated with sensory fibers of the ciliary nerve, a branch of the massive trigeminal nerve that brings touch, temperature and pain sensations from the face and front of the head. The cornea also receives a smaller number of autonomic motor fibers that activate the lachrymal (tear) glands. Free nerve endings detect syn-propanethial-S-oxide on the cornea and drive activity in the ciliary nerve–which the central nervous system interprets as a burning sensation–in proportion to the compound’s concentration. This nerve activity reflexively activates the autonomic fibers, which then carry a signal back to the eye ordering the lachrymal glands to wash the irritant away.

That process* is completely unaffected by whether you happen to be chewing gum while cutting the onion. However, chewing gum might make you blink your eyes more often, and at the very least gives you something to concentrate on other than watery eyes.
If you’ve got some onions that really tear you up, cutting them under water is a proven approach to tear reduction. The gas is water soluble.
*Several sites, including wikipedia, claim that the lachrymator works by hydrolyzing to sulfuric acid on the surface of the eye. The implication is that sulfuric acid is the ultimate irritant responsible for tears. Although this makes a nice little story, I’ve found no evidence that’s it’s actually true. Lots of things irritate eyes without turning into H[sub]2[/sub]SO[sub]4[/sub] and I see no reason that syn-propanethial-S-oxide couldn’t be one of them.

[Hosay]

Thank You Squink

[According_to_Pliny]

Martha Stewart endorses the old advice to cut them under water. Also, some varieties don’t cause tears. I like red onions for that reason.

[Chance_the_Gardener]

If you hold a couple of matchsticks in your mouth while cutting up onions, heads out, the tearing effect isn’t so bad. This works for me.

Hint from Heloise: don’t light the matchsticks before or while they’re in your mouth.

[BrandonR]

My contacts seem to make my eyes invincible against the onion.

[Chefguy]

Cutting them under water can be awkward. It’s almost as effective to wet your wrists and forearms before chopping.

[BarnOwl]

How about wearing swimmer’s goggles?

It might look idiotic, but if it works better than cutting onions under water, what do you care?

[Quiddity_Glomfuster]

I’ve found it also helps to stand back and lean away from the onion. Sounds goofy, but you tend to bend over your work and look directly down - the onion vapours then rise directly into your eyes. If you cut them at arms’ length, you won’t be in the direct line of fire.

Mind you, I generally avoid the problem completely by using sweet onions, which I like much better.