Why Do Onion make you cry?


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

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