Chop Onions, Cry: The Science Behind the Tears

Chop Onions, Cry: The Science Behind the Tears

We've all experienced it – the moment when you start chopping onions and tears start rolling down your cheeks. It's as if the onions have some magical power to bring forth an emotional outpouring. But fear not, my fellow home cooks and culinary enthusiasts, for we shall dive into the fascinating science behind this tear-inducing phenomenon. So, grab your tissues and let's uncover the mystery of why onions make you cry when you chop them.

The Culprit: A Volatile Compound

The main culprit behind the onion-induced tears is a volatile compound called syn-propanethial-S-oxide. Don't worry if it sounds like a complex scientific term – we'll break it down for you. When you chop an onion, you rupture its cells, releasing this volatile compound into the air.

The Dance of Chemistry

As this tear-inducing compound wafts into the air, it comes into contact with the moisture in your eyes. When these two substances mingle, a chemical reaction occurs. The syn-propanethial-S-oxide activates your eyes' lachrymal glands, and voila! Tears start flowing.

Evolutionary Woes

Now, you might wonder why on earth onions have evolved to be tear-jerking agents. The answer lies in the onion's defense mechanism against herbivores and pests. By releasing this eye-irritating compound, onions deter animals from munching on them, thus ensuring their survival in the wild.

A Story from the Past

Imagine our ancestors foraging for food in the wilderness. They would stumble upon wild onions and, like us, experience the same teary-eyed encounter. Yet, they recognized the significance of this phenomenon. It served as a signal – "Beware! These onions are not to be trifled with."

The Modern-Day Culinary Dilemma

As we've progressed from foragers to gourmets, our love for onions has remained steadfast. We've cultivated and consumed them in various dishes throughout human history. But with every chop, the same tearful reaction lingers.

Taming the Tears: Myth vs. Reality

Now, let's explore some of the popular methods for curbing the waterworks and separate the myths from the reality.

Method 1: Chilling the Onion

Myth: Keeping onions in the refrigerator before chopping will completely eliminate tears. Reality: While refrigerating onions can slow down the release of the tear-inducing compound, it won't entirely prevent tears and affects how the onion is cooked.

Method 2: Cutting Underwater

Myth: Chopping onions under running water or submerging them in water will prevent tear production. Reality: While this method may reduce the amount of tear gas that reaches your eyes, it's impractical and can make the chopping process more challenging. No one wants to loose a finger.

Method 3: Freezing the Onion

Myth: Freezing onions before chopping will prevent the release of tear-inducing compounds. Reality: Freezing onions can help reduce the volatility of the compounds, but it won't stop them from causing tears altogether. Also, how do you chop a frozen onion?

Method 4: Wearing Goggles

Myth: Wearing swimming goggles or any other form of eye protection will keep your eyes tear-free. Reality: While it might seem like a clever solution, wearing goggles in the kitchen might not be the most convenient or stylish option. The onion gas still gets to your eyes through your nose via the nano-lacrimal duct. This makes onion goggles useless.

Practical Solutions - Spoiler alert none of them are 100% except for one....

Although we can't completely escape the tearful fate when chopping onions, several practical tips can help minimize the tears and make the process more bearable.

Tip 1: Sharp Knife Skills

Using a sharp knife to chop onions causes less cell damage, which means fewer tear-inducing compounds are released. Invest in a good-quality chef's knife and keep it sharp.

Tip 2: Proper Ventilation

Working in a well-ventilated area can help disperse the tear gas, preventing it from accumulating near your eyes. Switch on the exhaust fan or open a window while chopping onions.

Tip 3: Onion Slicing Technique

Mastering the art of onion slicing can significantly reduce tear production. Try cutting the onion vertically or placing the onion's root end farthest from you to minimize exposure to the compounds.

Tip 4: The Laughing Onion

The laughing onion is the only 100% effective way to prevent the onion gas from reaching your eyes and causing you to cry buring tears while chopping, cutting or slicing onions. You simply turn it on, place it next to the chopping board and it laughs the tear inducing onion gas away for good! No misted up goggle that don't work, no trying to cut a frozen onion...


In conclusion, the tears that accompany chopping onions are a result of a fascinating chemical reaction between syn-propanethial-S-oxide and our tear ducts. While we may shed tears in the kitchen, let's remember that this onion-induced weeping is a testament to the remarkable defense mechanism of this humble vegetable.

The next time you chop onions, arm yourself with the laughing onion and the knowledge of why tears flow, so that the onions won't make you cry. Chop onions, cry no more, and let the delicious flavors they bring to our dishes make it all laughter from prep!

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