Why Does an Onion Make You Cry?

January 23, 2023

Onion being chopped

You can sniff an onion or peel the layers without shedding a tear, but once you crush, chop, or cut an onion, there’s a good chance those tear ducts will start working. The thing that is causing you to tear up is actually a defense mechanism of the onion to deter intruders from eating it when it was in the ground.

An onion bulb is composed of many rectangular cells, and within each of the cells are vacuoles. The vacuoles are spaces enclosed by a membrane filled with an enzyme called lachrymatory factor synthase, or LF, which is an irritant.

When these vacuoles break open, like they would be when they are cut, LF is released. This enzyme then mixes with the contents of the onion cell, which contain sulfenic acid, and a chemical reaction begins to take place. The result of the chemical reaction produces a gas called syn-propanethial-S-oxide, which floats into the air and can quickly irritate a person’s eyes. The nerves in the eye then react to the gas and produce tears to try to get rid of the irritant. This is the complex process that makes us cry while cutting onions.

This chemical reaction is more pronounced in some varieties of onion over others. Red, white, and yellow onions have higher concentrations of LF while green onions, scallions, and sweet onions contain lower concentrations. That’s why all onions don’t necessarily cause you to tear up.

What’s the best way to not tear up while cutting an onion? There are a couple of simple options. One is to cut onions in a well-ventilated area or with a fan present to blow the gas released by the onion away from the face. Another option is to refrigerate the onion before chopping, which makes the molecules move slower and the chemical compounds less volatile.

Other onion facts that don’t have to do with tears

According to the National Onion Association, the average American eats 20 pounds of onions per year, and 450 semi-truck loads of onions are consumed every day in the United States.

The country with the highest per capita consumption of onions is Libya. People in this country consume 66.8 pounds of onions per person each year.

The largest onion in the world was grown by Tony Glover of Leicestershire, England, in 2014. It weighed 18 lbs 11 oz and was 32 inches around its widest part.

The state vegetable of Texas is the 1015 sweet onion. It was developed by a Texas A&M horticultural professor in the 1980s and got its name from the optimal planting date for the onion on October 15th. It grows only in the Rio Grande Valley of South Texas.

The state vegetable of Georgia is the Vidalia onion. It is only grown in a small portion of southern Georgia.

The country with the largest onion production in 2020 was India at 26.74 million metric tons. China was next at 23.66 million metric tons, followed by the United States at 3.82 million metric tons.

Sources: WebMD, NPR, US Library of Congress, National Onion Association, NY Times, Metro UK, Bristol Farms, State Symbols USA, World Atlas

About the author 

Daniel Ganninger - The writer, editor, and chief lackey of Knowledge Stew, the author of the Knowledge Stew line of trivia books, and editor of Fact World and the Knowledge Stew sister site on Medium, our ad-free subscription sites. I hope you learn many new things here that add to your knowledge.

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