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Why do onions make our eyes water?

Question #26924. Asked by whoknows.
Last updated Apr 27 2023.

KIWI INOZ
Answer has 2 votes
KIWI INOZ

Answer has 2 votes.
If you looked at an onion under a microscope you would see it consists of lots of little sacs similar to an orange or a lemon. When you cut through it, these little sacs burst, spraying juice about and releasing fumes which affect some people worse than others.

This also accounts for why some recipes call for onions to be chopped finely and others roughly or sliced. The more you chop an onion the more flavour you will get through the breakage of the little sacs.

Jan 23 2003, 9:34 PM
Kainantu
Answer has 4 votes
Kainantu

Answer has 4 votes.
When onions are cut or even bruised, their cell walls are broken and a volatile sulphurous compound with the help of an enzyme in the onion juice turns into an acid that causes the burn. Fortunately, food scientists tell us, the acid disperses quickly taking the burn with it.

link http://www.pbs.org/newshour/rundown/why-do-onions-make-us-cry/

Onions contain a molecular cousin of sulphuric acid known as allinin.


Response last updated by gtho4 on Apr 27 2023.
Jan 25 2003, 11:46 AM
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Professer
Answer has 4 votes
Professer
17 year member
56 replies avatar

Answer has 4 votes.
Onions may cause your eyes to tear for the following reason:

When you cut into an onion, you slice through cells which contain sulfur compounds. Sulfur is quite a noxious (bad smelling)element. The compounds released are highly volatile, meaning they quickly enter the air in their vicinity. Your eyes produce tears because your body wants to wash or dilute the chemicals before they effect your eyes. The tears are a natural way the body can wash the offensive chemicals away.

link https://www.sundaystandard.info/why-do-onions-make-you-cry/


Response last updated by gtho4 on Apr 27 2023.
Jun 15 2008, 4:50 AM
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McGruff star
Answer has 4 votes
McGruff star
Moderator
24 year member
3694 replies avatar

Answer has 4 votes.
When they are sliced open enzymes escape. The enzymes decompose some of the other substances that have escaped like amino acid sulphoxides and form sulphenic acids. These become 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. The nerve endings in your eyes are very sensitive and react quite violently to this irritation.

From the site Howstuffworks:

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.



Response last updated by gtho4 on Sep 11 2016.
Jun 15 2008, 8:11 AM
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McGruff star
Answer has 5 votes
Currently Best Answer
McGruff star
Moderator
24 year member
3694 replies avatar

Answer has 5 votes.

Currently voted the best answer.
Cutting an onion arouses a gas contained within the onion, propanethiol S-oxide, which then couples with the enzymes in the onion to emit a passive sulfur compound. Our tear ducts react by releasing tears (when blinking) to flush out the sulphuric acid.

When slicing onions I generally have overhead fans on, and once the outer skin is removed I wash them under cold water before making the first incision. Definitely no tears.

link https://www.washingtonpost.com/archive/lifestyle/2003/01/03/what-is-it-in-onions-that-mak/9c7afd73-c915-48f4-85dc-e508c55b6429/


Response last updated by gtho4 on Apr 27 2023.
Jun 15 2008, 8:22 AM
jk18
Answer has 3 votes
jk18

Answer has 3 votes.
Propanethial-S-oxide is a gas that's released when the cell wall of an onion is broken. This gas reacts with the water in your eyes and produces sulphuric acid. Getting acid in your eyes sucks, it also burns.

link http://everything2.com/e2node/Why%2520onions%2520make%2520your%2520eyes%2520water

Jun 18 2008, 11:25 AM
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