Onion Tear Gas: Why Your Eyes Water and How an Electric Chopper Helps

Which Gas Comes Out When You Cut an Onion? (Onion Tear Gas)

The gas that comes out when you cut an onion is syn-propanethial-S-oxide. Scientists call it the onion's lachrymatory factor, which simply means the tear-making chemical. That is why people call it onion tear gas. The gas rises from the cut onion and irritates your eyes. Your eyes then make tears to wash it away. Scientists see it as part of the onion's chemical defence against microbes and animals.

The Library of Congress puts it in two lines: “Onions produce the chemical irritant known as syn-Propanethial-S-oxide. It stimulates the eyes’ lachrymal glands so they release tears.”

Why Do Onions Make You Cry? The Simple Chain

Here is the simple chain. You cut the onion and break its cells. First, an enzyme called alliinase breaks down the onion's sulfur compounds. Then a second enzyme, lachrymatory-factor synthase, turns the result into syn-propanethial-S-oxide. This gas is volatile, which means it turns into vapour very easily. It drifts up from the board toward your face. When it reaches your eyes, it irritates them. Your tear glands then make tears to wash it away.

Key fact: Scientists Brodnitz and Pascale named this tear-making gas in 1971. They called it thiopropanal S-oxide. In 2002, Imai and his team at House Foods in Japan found the enzyme that makes it. They reported it in the journal Nature as “an onion enzyme that makes the eyes water”. In 2016, the same company reported tearless onions in the journal Scientific Reports. A panel of 20 tasters felt no tears from them, and they made about 7.5 times less tear gas than normal onions.

The gas only forms when onion cells are damaged, so a whole, uncut onion does not make you cry. A sharp knife crushes fewer cells than a blunt one, so it should release less gas. But even a sharp knife cannot stop all of it. That is where a closed chopping bowl comes in.

प्याज काटने पर कौन सी गैस निकलती है?

प्याज काटने पर सिन-प्रोपेनथियल-एस-ऑक्साइड (syn-propanethial-S-oxide) नाम की गैस निकलती है। यह गैस हवा में ऊपर उठकर आँखों तक पहुँचती है और आँखों में जलन करती है। प्याज काटने पर आंसू क्यों आते हैं? क्योंकि आँखें इस गैस को धोने के लिए आँसू बनाती हैं।

In Hinglish: Pyaj me konsi gas hoti hai? Pyaz katne par syn-propanethial-S-oxide naam ki gas nikalti hai. Yeh gas aankhon ko chubhti hai, isliye aansu aate hain. (In English: cutting an onion releases a gas called syn-propanethial-S-oxide. It stings your eyes, so you cry.)

Onion Cut Karne Par Aansu Kyu Aate Hai?

Onion cut karne par uske cells toot jaate hain. Cells ke andar ke enzyme mil kar tear gas banate hain. Yeh gas aankh tak pahunchti hai, aur aankh use dhone ke liye aansu banati hai. (In English: cutting breaks the onion's cells, two enzymes make the tear gas, and your eyes make tears to wash it away.)

How an Electric Chopper's Closed Bowl Cuts the Tears

An electric vegetable chopper cuts the onion inside a closed bowl with the lid on. Most of the syn-propanethial-S-oxide gas stays inside the bowl while the blades run. It does not rise straight into your face, as it does from a chopping board. Some gas still comes out when you lift the lid. So open the lid away from your face and step back for a moment.

Think of it like chopping inside a tiny closed room. The gas stays in the room, not in your face. You should get far fewer tears this way. You may still feel a little sting when the lid comes off.

Try a simple test in your own kitchen. Cut one onion with a knife. Then chop one in the InstaCuppa Electric Chopper with the lid on, and compare how your eyes feel. The closed bowl is what keeps the gas away from your eyes.

Research note: The Library of Congress explains that the tear gas forms only after the onion is cut. Then the gas gets into the air and reaches your eyes. A closed bowl keeps that air away from your face while you chop. The American Academy of Ophthalmology gives three more tips: keep the kitchen breezy, chill the onions, and try onion goggles.

7 Onion Tear Hacks People Try (and Which Ones Work)

Every Indian kitchen has a favourite onion hack. Three of them have backing from the American Academy of Ophthalmology: a breezy kitchen, chilled onions, and onion goggles. For the rest, we say plainly when we found no study.

The most practical solution for daily Indian cooking is a sealed electric chopper. You do not need goggles, candles, or a running tap. Just quarter the onion, drop it in the bowl, press the button, and open the lid a few seconds later.

Best Onion Chopper Setup for Indian Cooking

For daily onion chopping in an Indian kitchen, a plug-in electric chopper with a lidded bowl is the simplest option. A 500 ml bowl suits small daily batches. You get even pieces with fewer tears, less mess, and no knife skill needed.

For large families (5+ people): The InstaCuppa Premium Electric Chopper (2,000 ml, Rs 2,299 on 22 October 2026) has a bowl four times bigger than the 500 ml model, so it takes much larger batches. Three speed settings give you control over the chop size.

For 2-4 people: The InstaCuppa Electric Chopper (500 ml, 400 watts, Rs 2,199 on 22 October 2026) is the sweet spot. Comes with garlic peeler and egg beater too.

Read more about onion choppers: Best Onion Choppers in India 2026