It was such an interesting experience on my first time slicing an onion. I was much younger then and inexperienced in cooking. I had to run out of the kitchen when it reached a point I could barely take it anymore. As kids we were used to playing with the gas from orange peels but that emanating from an onion was much more irritating. Everyone slicing onions for a first time almost nearly cried, except you have never attempted it before.


According to information published by The New York Times, Onions produce the chemical irritant known as syn-propanethial-S-oxide. It stimulates the eyes’ lachrymal glands so they release tears. In the past, Scientists used to blame the enzyme allinase for the instability of substances in a cut onion. The synthase enzyme converts the amino acids sulfoxides of the onion into sulfenic acid. Onions make us teary because a reaction in the onion releases a chemical called lachrymatory factor, or LF, that irritates our eyes. Gently peeling the outer layer of an onion won’t make your eyes water. But cutting, grinding or distorting its flesh breaks open the cells which releases the irritant substances which hits the sensory nerves in the eyes and causes them to tear up.

A paper published in July in the journal ACS Chemical Biology, syn-propanethial-S-oxide or Lachrymatory factor is similar to tear gas. It evolved as a defense mechanism to protect onions against microbes and animals like man. Damaging an onion provokes a reactive response from its defenses by a chemical reaction. 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 floating in that cytoplasm are little sacs called vacuoles, containing a protein called alliinase. “One has not seen the other, but if you damage the cells, they can now meet and make these reactions,” said Marcin Golczak, a biochemist at Case Western Reserve and principal investigator of the latest study. The molecule and the protein fit together perfectly, the chemical structure of the molecules change, and that lazy floater becomes a fully armed soldier defending itself from an invasion with irritant tear gas.

Apart from onions which other plant can make us tear

Apart from Onions, only two other plants are known to contain LF: guinea hen weed, (Petriveria alliacea) and Sicilian honey garlic (Allium siculum), but we are very less likely to encounter them as they have far less economic value. Worldwide, onions is consumed in tremendous quantities every year. The flavour and aroma of food spiced with onions is not just fascinating but irreplaceable. That means we will continue sobbing for a longer time. It has not been substantiated however why some people tear more than others. I know you are probably asking now, if there is anyway to avoid the gas while slicing. In Japan, scientists engineered a tearless onion but lacks that signature onion flavor: “The taste is completely different,” Dr. Golczak said.

How to reduce the effect of the gaseous reactions in an onion

1. You can freeze the onions a little before chopping or slicing. By reducing the temperature, the severity of the reaction of the gases also reduces tremendously resulting in less LF.

2. Slice or grind the onions in water, the water dilutes the gasses and reduces its potency.Cut the root last, it has a higher concentration of enzymes.

3. Use of sharp knife to cut the onion releases less of the enzymes into the air.

4. Wear kitchen goggles to protect your eyes.

You must also note that freezing onions or immersing it in water also changes the flavour that it produces.

There is no easy way about it. People who deal with onions everyday feel less teary. As for me, am not sure I can do without the onions flavour in my recipe. After all releasing tears sometime is also good for health

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