why do we get tears when cutting onions ?

Answer 1

This is from howstuffworks.com

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.

Answer 2

The tearjerker in onions is a compound called propanethial-s-oxide, which is released in a vapor when onions are cut .

When the vapor comes in contact with the eye, it is converted to a form of sulfuric acid, which produces the stinging sensation and subsequent tears.

Cutting onions under water or chilling them before cutting, will retard the enzymes that generate the noxious chemicals.

Some other suggestions people have mentioned for preventing tears when working with onions include:

Keep the root on while peeling and chopping. A variation of this is to cut from the top leaving the root end intact until the last cut!

Be in a well-ventilated place and cut fast!

Use a good, sharp chef's knife. It glides through the onion with ease, allowing less of the compounds that cause tears to come out.

Wear a pair of safety goggles or a cheap, disposable painter's mask.

Put a slice of bread in your mouth, with half of it sticking out to "catch" the fumes.

Put some white vinegar on the chopping board before cutting.

Burn a candle immediately adjacent to where you're cutting. The tear-causing gas is drawn toward the heat source.

Answer 3

As onions are sliced, cells are broken open. Onion cells have two sections, one with enzymes called alliinases, the other with sulfides (amino acid sulfoxides). The enzymes break down the sulfides and generate sulfenic acids. Sulfenic acids are unstable and decompose into a volatile gas called syn-propanethial-S-oxide. The gas then dissipates through the air and eventually reaches one's eye, where it will react with the water to form a mild solution of sulfuric acid. The sulfuric acid irritates the nerve endings in the eyes, making them sting. The tear glands then produce tears in response to this irritation, to dilute and flush out the irritant.

A firm in Toronto, Canada, attempted to utilize this property of onions in the manufacture of a form of tear gas for civilian use. It was marketed in 1991 but was unsuccessful as it had an effective shelf life of only three months.

The release of gas can thus best be prevented by cutting the onions under running tap water or completely under water, though this may not be very practical. Wetting the onions and your hands before slicing will lessen the effect, as some of the gas will react with the moisture on the onions and on your skin (instead of the moisture on your eyes). This reaction may result as an odour which may be removed with lemon. It also helps to breathe exclusively through the mouth during the preparation. Using a sharp knife will rupture fewer cells and cause less eye irritation. For more tips and information, please check links in External links section. Chilled onions (onions kept in the fridge for a while) will make you 'cry' less than onions kept at room temperature because lower temperature inhibits the enzymes and gas diffusion. Also, some people 'freeze' the knife (leave it in the freezer for around 2 minutes) before cutting the onions to prevent the tears.

Different species of onions will release different amounts of sulfenic acids, thus some will cause more tear formation and irritation than others.

Answer 4

Onions contain Hydrogen Sulfide. It's one of those natural things that keeps the rabbits and other beasties from eating an onion. For us, it's an irritant, especially if you forget to wash your hands, then rub your eyes. I'm tellin' ya.

As humans, we are lucky - we have skillets, and olive oil. Yummmm, onions!

Answer 5

the others are telling you like it is!
but do you know that if you stick your head in your freezer and take a deep breath your; eyes wont tear up== try it it really helps

Answer 6

my sister in law told me a trick. put a piece of bread in your mouth while you are cutting the onion. you will not be teary. i havent tried it yet, but she swears it works!!!!

Answer 7

i don't now, but if you sprinkler some salt on it you won't get any tears

Answer 8

2nd Answer - Butterfly - has it figured out

good luck

Answer 9

good point