Why tears come when we cut onions?

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  • mom answered 7 years ago
♥ ♥ some chemical reaction... if you chew on a toothpick while cutting onions you wont cry ♥ ♥
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  • swati answered 7 years ago
    We all know that onions make us tear up. The next time you are around someone who is cutting up an onion, impress them with your scientific knowledge.

    Onions contain amino acid sulfoxides, which are a type of organic molecule. When you cut into the onion skin, allinases, a class of enzymes, mix with the sulfoxides to make sulfenic acid. Once exposed to oxygen in the air, the sulfenic acid arranges into the strong chemicals syn-propanethial-S-oxide and thiosulfinates, which cause tears and cause the strong smell of cut onion, respectively. It's not the scent of the onion that makes you cry, but rather the syn-propanethial-S-oxide irritating the eye that makes you release reflex tears and cry. Since the chemical makes you cry it's also called a lachrymator.
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  • Bombazine_Doll. answered 7 years ago
    Onions contain a sulferic compound that irritates the eyes. The compound is, however, water soluble, and your eyes water to try to dilute the compound and wash it away from your eyes.

    Tip: If you cut the onion while holding it under a spray of water, the chemicals will wash down the drain and will not enter the air in as great an amount to cause your eyes irritation.

    Source(s):

    http://www.newton.dep.anl.gov/askasci/bio99/bio99086.htm
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  • novae2 answered 7 years ago
    The onion contains some substances which contain sulfur. Sulfur is an irritant to both our noses and to our eyes. Cutting an onion releases these sulfur compounds. When these sulfur compounds come in contact with the water in our eyes, they produces sulfuric acid.

    Sulfuric acid irritates the eyes. In response to this acid, our eyes automatically blink, and produce tears which wash the eye and flush out the acid.
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  • unicorn answered 7 years ago
    because it contains a volatile oil which causes irritation to eyes.
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  • moonlight answered 7 years ago
    as onions are sliced,cells are broken open.onion cells have two sections,one with enzymes called alliinases,the other with sulfides(amino acid sulphoxides).the enzymes break down the sulphides and generate sulphenic acids.sulphenic 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 dilute solution of sulphuric acids.the sulphuric acid irritates the nerve endings in the eyes,making them sting.the tear glands then produce tears to dilute and flush out the irritant.

    Source(s):

    en.wikipedia.org/onion#onions & crying
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  • kelly answered 7 years ago
    coz it contains sulphur which when comes in contact with eyes via air then it irritates the eyes and then we ub our eyes.........
    so this way tears comes out from our eyes when we cut onions......
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  • Prasun Saurav answered 7 years ago
    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:

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

    And that's how tears come when we cut onions.
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  • RRAJAPRIYAR answered 7 years ago
    As onions are sliced, cells are broken open. Onion cells have two sections, one with enzymes called alliinases, the other with sulfides (amino acid sulphoxides). The enzymes break down the sulphides and generate sulphenic acids. Sulphenic 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 dilute solution of sulphuric acid. The sulphuric acid irritates the nerve endings in the eyes, making them sting. The tear glands then produce tears to dilute and flush out the irritant

    Source(s):

    science books
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  • srinu710 answered 7 years ago
    b ecause it contains elements like sulphur.
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  • Mansi P answered 7 years ago
    As we all know that there are layer in onion well why do we cry when we cut onions as you ask. One of the layers take out this thing that irritate you eyes and tears come out
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  • Darkstar answered 7 years ago
    a chemical or fume irritates the eye. good ?
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