Have you ever started chopping onions and suddenly felt your eyes fill with tears? It happens so fast that it feels almost magical—but there’s actually a clear science behind it.

Today, we’ll explore why onions make us cry, why some onions are worse than others, and what we can do to keep our eyes dry while cooking.

The Chemicals Inside Onions

Onions are packed with chemical compounds, but the ones responsible for tears are sulfur-containing compounds. Inside a whole onion, these chemicals are safely separated within its cells. Each cell has two main parts:

- Sulfur-containing amino acids, known as precursor compounds.

- Enzymes, like alliinase, that help trigger chemical reactions.

When the onion is uncut, these compounds never meet. No reaction happens, and our eyes stay perfectly dry.

What Happens When We Cut Onions?

The moment we slice an onion, the cells are damaged, allowing the enzymes and sulfur compounds to mix. This sparks a chemical reaction: sulfur amino acids break down into sulfenic acids.

These acids quickly rearrange into a volatile gas called syn-propanethial-S-oxide, which is also called the onion’s tear factor. This gas floats into the air almost instantly and can reach our eyes in seconds.

How the Tear Factor Affects Our Eyes?

When this tear factor reaches our eyes, it dissolves in the water of our tear film and forms a mild sulfuric acid. Even though it’s weak, it irritates the delicate membranes of the eyes. In response, our tear glands kick into action, producing more tears to wash away the irritant. That’s why our eyes water so easily while chopping onions.

Why Some Onions Make Us Cry More?

Not all onions are created equal. Different onion varieties have different amounts of sulfur compounds, which affects how much tear factor they release. Sharp onions like yellow and white onions have higher sulfur content, so they often cause more tears. On the other hand, sweet onions or green onions contain less sulfur, making them less likely to make our eyes water.

Practical Ways We Can Reduce Onion Tears

The good news is, there are several simple tricks we can use to chop onions without crying:

- Use a sharp blade: A sharp blade damages fewer cells, releasing less of the tear-inducing gas.

- Chill the onion first: Placing onions in cold water or freezing them for a few minutes slows down the chemical reaction.

- Use a fan: A small kitchen fan can blow the gas away before it reaches our eyes.

- Wear goggles: Even simple swimming goggles act as a physical barrier to protect our eyes completely.

- Cut near running water: The water can help capture some of the gas before it reaches our eyes.

By combining a few of these methods, we can dramatically reduce tears and make chopping onions a lot more comfortable.

Other Health Benefits of Onions

Onions are more than just tear-inducers—they’re surprisingly good for our health. The sulfur compounds and antioxidants in onions can help reduce inflammation, support heart health, and even act as natural antibacterial agents. They may not replace medicine, but including onions in our meals can quietly benefit our overall wellness. So while they might make us cry in the kitchen, onions are still an important part of a healthy diet.

Keep Tears Away!

Next time we chop onions, we can see it as more than just a tearful task. By understanding the science behind those tears and using simple tricks, we can keep our eyes dry and still enjoy all the flavor and benefits onions bring to our meals. Cooking can stay fun, safe, and tear-free, and we can even appreciate the small chemistry lesson happening in our kitchen!