New & NowFood Science

We Finally Know Why Onions Make Us Cry

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My consistent tearjerkers: this video of a lion being reunited with its owners after years of separation, the last chapter of Charlotte’s Web, Whitney Houston’s rendition of the Star Spangled Banner, and cutting onions. And while three of those would take longer to unpack than I have the time for, at least I can now confidently say I understand what it is about an onion that makes the tears flow.

Stop Crying Over Chopped Onions
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Stop Crying Over Chopped Onions

The allium’s signature pungent taste is actually the result of a biochemical defense mechanism, called a lachrymatory factor, that onions use to protect themselves against microbes and animal predators. This lachrymatory factor is loaded with sulfur oxide—the chemical compound that causes your eyes to sting and tear ducts to overflow. Up until now, however, scientists couldn’t quite place their fingers on what exactly caused the onion to produce this lachrymatory factor.

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To unearth the answer, researchers from Case Western Reserve University in Cleveland, Ohio focused their efforts on the lachrymatory factor synthase, an enzyme that the onion converts into sulfuric acid. By analyzing said enzyme up close and comparing it to similar organic structures, the scientists emerged with a more intricate understanding of what it is about an onion's molecular construction that allows for the creation of the much-derided kitchen tear gas. The full scientific explanation involves talk of proton transfer and ionic organization that goes a little over my head, but the scientifically inclined can get into the nitty gritty of the study here.

Unfortunately this new information doesn't really help us prevent our onion-chopping tears, so do your best to minimize them by using a very sharp knife and keeping the cut side down. In the meantime, I’ll be over here watching Christian the Lion kissing his owners, blaming all my tears on the enzymes in a freshly chopped onion.

Tags: onions, science, cry, reason, scientists