Why Do Onions Make You Cry? Plus How to Cut Them Without Tears

You start chopping an onion and within seconds your eyes sting and the tears are flowing. You’re not sad, so why are you crying? The culprit is an invisible gas the onion makes to protect itself.

What happens the moment you cut an onion

Inside an onion’s cells, sulfur-containing compounds and an enzyme that changes them are stored separately. Normally they never meet, but when a knife breaks the cells open, the two mix.

That sets off a few steps of chemical reactions that produce a volatile, eye-irritating gas. The gas drifts up into the air and reaches your eyes.

Why you tear up

When the gas meets the moisture on the surface of your eyes, it stimulates the nerves there and you feel a stinging burn. Your body responds by flooding your eyes with tears to wash the irritant away. It’s the same protective reflex as when dust gets in your eye.

From the onion’s point of view, it’s a kind of defense weapon to stop animals from munching on it.

How to cry less

• Use a sharp knife. A dull knife crushes and bursts more cells, releasing more gas. A clean cut with a sharp blade stings much less.
• Chill the onion. Putting it in the fridge before chopping means less gas rises into the air.
• Cut the root end last. The root area tends to have more of the irritating compounds, so leaving it for last helps.
• Use airflow. Turning on the range hood or opening a window keeps more of the gas away from your eyes.
• Try water. Many people find that briefly soaking a peeled onion in water before cutting makes it less harsh.
• Swim goggles work too. They may look a little silly, but they block your eyes completely.

Are there onions that don’t make you cry?

Onion varieties bred to release fewer of the irritating compounds are reported to exist. And cooking changes those compounds, which is why sautéed or roasted onions taste sweet instead of sharp.

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In one line

Cutting an onion mixes compounds inside its cells, making a gas that irritates your eyes, and your eyes cry to wash it away. A sharp knife and a chilled onion alone can save you a lot of tears.

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