Q&A

Why do onions make us cry? Gas

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Q Why do onions make you cry?

A Trying to figure out why humans cry is exhausting. We cry about death, break-ups, sweet kisses. We don't cry when we should, and we cry for no reason. But let's take a moment to appreciate the clarity of crying while cutting onions.

Onions make us teary because a reaction in the bulb releases a chemical called lachrymatory factor, or LF, that irritates our eyes. Peeling an onion won't make your eyes water. But if you chop, cut or crush one - boohoo. The onion's cells break open, allowing two normally separated substances to combine.

Linked together like pieces of a puzzle, they become a potent chemical weapon.

"It turns into a gas. It hits your eyes, and then it hits the sensory nerves in your eyes and causes them to tear up," said Ms Josie Silvaroli, an undergraduate at Case Western Reserve University in Ohio who helped describe the process in a paper published in the journal ACS Chemical Biology.

Lachrymatory factor evolved as a defence mechanism, protecting onions against microbes and animals. Damaging an onion causes it to ramp up its defences: As cells break, the chemical reaction is unlocked.

Inside the intact cells of an onion, a molecule called sulfenic acid precursor floats around the watery filler like a napping human in a lazy river. Also in that cytoplasm are little sacs called vacuoles, containing a protein called alliinase, which is like a little drill sergeant of the process.

"One has not seen the other, but if you damage the cells, they can now meet and make these reactions," said Dr Marcin Golczak, a biochemist at Case Western Reserve and the study's main investigator.

Can you avoid the onion feelies?

In Japan, scientists engineered a tearless onion. But it lacks that signature onion flavour.

With regular onions, there are options: Chuck your onion in the fridge before cutting or submerge it in water while chopping. These, however, will alter the flavour.

Unfortunately, it seems there is no simple way to avoid it. For the love of onions, sometimes you just have to cry.

NYTIMES

A version of this article appeared in the print edition of The Straits Times on September 15, 2017, with the headline 'Why do onions make us cry? Gas'. Print Edition | Subscribe