It’s more technical than you think…
The Bottom Line
When you cut into an onion it produces the chemical irritant known as syn-propanethial-S-oxide. It stimulates the eyes’ lachrymal glands so they release tears.
The process goes as follows:
- Lachrymatory-factor synthase is released into the air when we cut an onion.
- The synthase enzyme converts the sulfoxides (amino acids) 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!
Preventing you eyes from coming into contact with this chemical will prevent the irritation which causes tears. I guess you could use a mask and snorkel if you really wanted to…
Additional science fact: According to the Guiness Book of World Records, the largest onion weighed 10 pounds 14 ounces. It was grown by V. Throup of Silsden, England.