Why Do Onions Make You Cry?

People put up with the tears associated with cutting onions to take advantage of their distinctive taste and health benefits.

The onion is a vegetable that people use in the kitchen as a cooking ingredient. It is closely related to garlic, Chinese onion, leek, and shallot, among other vegetables. In 2014, the countries that produced the largest amounts of onions were China and India. China produced 25% while India produced 22% of the world’s onions. Crying when cutting onions is the result of reflexive tears. The tears are a result of the rupturing of onion cells and the subsequent release of the lachrymatory factor (LF) which is the underlying cause of the irritation of the eyes. The LF is a defense weapon that onions develop to protect themselves from microbes and animals including humans. However, people choose to bear with the “crying” to enjoy its distinct flavor and health benefits.

Health Benefits

Onions have been known to have a medicinal value since the Roman emperor Nero used it to cure colds. They are also thought to have aided in the prevention of epidemics such as plague and cholera. Besides, onions have high nutritional value as they contain Vitamins A, B6, E, and C. They also have natural sugars, potassium, iron, sodium, iron, and dietary fiber. Furthermore, onions are an excellent source of folic acid. The enjoyment of most of these health benefits occurs when an individual eats the onion in its raw form. A compound known as allyl propyl disulfide gives onions its curative properties.

The Cause of Onion Tears

When one damages the onion cells by crushing, cutting or chopping the onions, there’s a release of Lachrymatory-factor synthase. The enzyme converts the amino acids sulfoxides inside the onion into sulfenic acid. Then a sulfur compound known as syn-propanethial-S-oxide is released in the air. This compound spreads to the eyes and mixes with the tears to form sulfuric acid. Sulfuric acid’s burning sensation results in the release of tears from one’s eye. The tears are the eye’s manner of washing away the irritation caused by the onions. The Lacrimal gland in the eye is responsible for producing the tears.

The Tearless Onion

Japanese scientists engineered tearless onions. In 2008, the New Zealand Institute for Crop and Food Research successfully created “no tears” onions. They did so by using gene-silencing biotechnology to prevent the normal synthesis of the LF synthase in onions. However, these onions do not have the unique flavor on onions.

How to Prevent Crying when Cutting Onions

One should cut onions in a well-ventilated area, near a fan if possible. The fan will blow air away from the eyes, pulling the onion molecules away with it, such that they will not get to the eyes. Another way of preventing crying is by refrigerating the onions before cutting them. Onion molecules are less volatile in their cold state than at room temperature. Thirdly, one may reduce eye irritation by slicing the onions under running water or by submerged in water. The water prevents the gas from spreading to the eyes. Lastly, cutting of the onion should be from top to bottom. The onion roots have the highest concentration of enzymes that irritate the eyes. Hence chopping the onion from top to bottom enables one to minimize the tearing of eyes.


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