why does tears come from our eyes while cutting onions?

Answer 1

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 sulfuric 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.

Oddly enough, this volatile compound is also responsible for a lot of the great taste in onions, as well as the pleasant aroma when you cook the vegetable. You'll also get sulfenic acids by cutting up garlic, chives and leeks, among other vegetables, but they don't form the same irritating gas, just a strong smell.

Answer 2

I used to think I was immune to crying when cutting onions...but later, after I decided to stop wearing contact lenses (which seemed to be my protection)...I looked so emotional cutting onions :). I found this answer on the net, could be a bit too scientific for me but a good answer none the less:

Onions produce the chemical irritant known as syn-propanethial-S-oxide. It stimulates the eyes' lachrymal glands so they release tears. Scientists used to blame the enzyme allinase for the instability of substances in a cut onion. Recent studies from Japan, however, proved that lachrymatory-factor synthase, (a previously undiscovered enzyme) is the culprit (Imani et al, 2002).

The process goes as follows:

Lachrymatory-factor synthase is released into the air when we cut an onion.
The synthase enzyme converts the sulfoxides (amino acids) of the onion into sulfenic acid.
The unstable sulfenic acid rearranges itself into syn-ropanethial-S-oxide.
Syn-propanethial-S-oxide gets into the air and comes in contact with our eyes. The lachrymal glands become irritated and produces the tears!

Answer 3

Onions contain sulfides, which are released and become airborne when they are being cut. These sulfides react with the water on and about a person's eyes to form sulfuric acid. Your eyes react to this unpleasant development by stimulating tear production.

The steps are more detailed where given in the sources below.

Answer 4

the reason why tears does from your eye on left is and can be different from the is and can of tearfrom the right eye of yours. now you ask the question why. i say have you ever seen vishnu cry with tears when he cut the onion. no you say right??
then I say have you ever seen the krishna cry from the tears of left eye? no you say right??
well that provens the fact that all three of you that is onion and vishnu and krishna and you be all the same. that means you are moronic vegetables. now remember this carefulyy ok

Answer 5

because it releases some sort of gas when you cut it?? I really don't know the details but if you peel an onion and put it in your fridge over night you will not cry cutting it! That's what i do and it works!!

Answer 6

because the onion has invisible fumes that get out when you cut it. you can avoid this by putting the onion under your water tap, so it washes it, do it before and after slicing the onion. this neutralizes the fumes...

Answer 7

the vapours from the onions that come out as your cut it burn your eyes , so your eyes produces tears to wash the vapours off

Answer 8

Because we are sad that we are killing an innocent root vegetable. Seriously, onions let off a gas that irritates your eyes that's why.

Answer 9

I don't know why exactly, but I can tell you that if you chew gum while cutting onions that you won't feel the urge to cry. Try it.

Answer 10

Because every time you cut an onion an angel dies.