Why do onions make you cry?

Picture by richard_north

Have you tried all the tricks like running your knife under cold water or keeping your onions in the refrigerator so they won’t make you cry when you cut them? Here is why onions make you cry. There is a chemical that irritates your eye’s tear glands (called lachrymal glands) and makes the eyes produce tears. Scientists used to blame another chemical called allinase for the effect that a cut onion would produce, but more recently Japanese scientists have discovered an enzyme that had not been previously known called the lachrymatory-factor synthase. When this enzyme is released from cutting an onion, another enzyme converts the amino acids in the onion. This then produces sulfenic acid. This chemical then rearranges the components into synropanethial-S-oxide. As this acid gets released into the air from cutting up an onion, it reaches our eyes and the lachrymal glands are agitated and the tear ducts respond by producing tears. Unstable chemicals are the cause of crying while we are cutting up onions. It may help to run a knife under cold water to help dispel the enzymes in the atmosphere and keep the vapors from reaching your tear ducts.