Why Do Onions Make Your Eyes Water?

United States
June 4, 2007 5:16am CST
I'm researching an article for this and I'm trying to word it correctly. Most of the information out there has to do with sulfur compounds, but it's not exactly clear. Please help!
1 person likes this
5 responses
@Cassy1976 (796)
• Australia
5 Jun 07
I have no idea why onions make your eyes water but I can give you a useless fact that I have learned, when I wear contact lenses my eyes dont water when I cut them up! I dont kno wif this helps you at all but I thought I would tell you anyway
2 people like this
• United States
7 Jun 07
Huh, that's really weird! I don't understand why that would happen. It seems like the tissues in your lachrymal glands would be the reactive part. If you find out why your don't cry when you have contacts in, let me know, would you?
1 person likes this
• Australia
7 Jun 07
I have no idea why it happens but I know that my sister in law is illergic to cats and her eyes swell up when she comes to visit and get all watery etc but if she wears contact lenses this doesnt happen, they must protect the eyes somehow
1 person likes this
@Nardz13 (5059)
• New Zealand
4 Jun 07
Hi there, 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. There are all kinds of remedies for dealing with this irritating phenomenon, some more effective than others. As a general rule, move your head as far away from the onion as you can, so the gas will mostly disperse before it reaches your eyes. If you really can't stand the tears, the simplest solution might be to wear goggles. This measure is very effective, but it may seem a bit extreme to those around you, and if your kitchen is steamy, you might not be able to see what you're doing (never a good idea when you're using a knife). Peeling the onion and then chilling it in the refrigerator before you slice it will minimize the release of gas somewhat, because the change in temperature alters the compounds in the onion. Cooking an onion before you slice it will work also, for the same reason. Another easy solution is to cut the onion under water or run the tap over it as you slice. This information is found at this link: http://www.mylot.com/nr/newresponse.aspx?p=1&qid=1122955
2 people like this
• United States
5 Jun 07
Oh wow, thank you!
1 person likes this
@Aneihs (66)
• Philippines
12 Sep 07
It is not the strong odor of the onion that makes us cry, but the gas that the onion releases when we sever this member of the lily family. The onion itself contains oil, which contains sulfur, an irritant to both our noses and to our eyes. 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. When this upwardly mobile gas encounters the water produced by the tear ducts in our eyelids, it produces sulfuric acid. In response to the caustic acid, our eyes automatically blink, and produce tears which irrigate the eye, and which flush out the sulfuric acid.
1 person likes this
• Philippines
18 Sep 07
The volatile oils that help to give Allium vegetables their distinctive flavors contain a class of organic molecules known as amino acid sulfoxides. Peeling, cutting, or crushing an onion's tissue releases enzymes called allinases, which convert these molecules to sulfenic acids. The sulfenic acids, in turn, spontaneously rearrange to form syn-propanethial-S-oxide, the chemical that triggers the tears. They also condense to form odorous thiosulfinates, coincindentally evoking the pungent odor associated with chopping onions and eliciting the false accusation that it is the odor that causes the weepy eye. Incidentally, sulfenic acid in garlic takes a different chemical route, sparing the eyes. 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 chemical and physical 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 automatic 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.
• United States
14 Sep 07
I learned why onions make you cry is because your knife isn't sharp.Yeah there was this thing on TV and this chef was tell all about it. I don't know if it works or not I haven't gave it a try but I guess it wouldn't hurt to try..