The Reasons Why Onions Make You Cry

It’s amazing to learn about the different natural defense mechanisms that animals and plants have. Living creatures are equipped with many ways to defend their territory or ward off threats, and many of these are automatic responses. One of these defense mechanisms that has fascinated scientists for decades comes from onions. Onions are a kitchen favorite and have the ability to transform raw and cooked dishes into something fragrance and delicious. Their magic comes with a small price, and many tears have been shed in cutting these flavor-packed vegetables. If you’ve ever wondered why this is so, the answer lies in a series of chemical reactions that take place when you start slicing.


Irritants in Your Eye

Most people are aware that onions release some kind of chemical that irritates the eye, but there are a few steps before that happens. Many plants, in defense, release bitter chemicals known as polyphenols when their cells are damaged. Onions release syn-propanethial-S-oxide, a more irritating compound, in an effort to prevent animals from eating the vegetable. Syn-propanethial-S-oxide is highly volatile, evaporates quickly, and ends up in the eyes where it dissolves to form sulfenic acid. Syn-propanethial-S-oxide is called a lachrymatory factor because it irritates and stimulates the tear gland which is also known as the lacrimal gland. Tears are produced involuntarily as a result.

A few chemical reactions must take place for syn-propanethial-S-oxide to be released from a bruised onion. It was initially believed that the entire reaction was triggered by a single enzyme, but thanks to research done in Japan in 2002, it has been proved that there are, in fact, two enzymes behind this.

As the onion grows, it absorbs sulfur from the ground. The amount of sulfur it absorbs depends on many factors including the soil it is growing in and the conditions. This has a bearing on the onion’s ability to make you cry because, as you might have experienced, different onions produce different levels of irritants. Sulfur in the onion is incorporated into complex compounds and amino acids in the onions such as PRENCSO (1-propenyl-L-cysteine sulphoxide). When you cut onions and damage the cells, the enzymes allicinase and lachrymatory-factor synthase are released. Allicinase reacts with PRENCSO to form amino acids sulfoxides. These react with the other enzyme, lachrymatory-factor synthase, to form sulfenic acid which converts to syn-propanethial-S-oxide. This is the substance that makes its way to your eyes and triggers the tears.

What Can You Do to Limit the Tears?

Scientists and layman alike have battled with this question for a long time. There are a number of things that might be able to make your onion-cutting experience less teary. They might not all be completely effective, but they are worth a try.

Some simple tricks and hacks to try include using a sharper knife to chop your onions. A blunt knife causes more damage to the onion cells, and that triggers the release of more irritants. You can also blanch the onions or store them in the fridge or freezer before you cut them. this damages the enzymes responsible for the chemical reactions detailed above but may also affect the flavor and form of the onions. Running water and even goggles can be used to divert the irritant chemicals from your eyes.

As discussed already, the onion’s type, growing conditions, and soil all affect how much sulfur and lachrymatory factor the onion has. Scientists are looking at making use of this knowledge to selectively breed onions that have less of the lachrymatory-factor synthase enzyme. Genetic engineering can also be a means to modify the genetic makeup of onions to achieve this. In all these methods being considered, the hope is that the amazing flavor of the onion is not going to be diminished.

Editor's Picks

reset password

Back to
log in