Why do onions make you cry?
Cutting an onion breaks its cells and starts a chemical reaction that releases an irritating gas. When the gas reaches your eyes, they make tears to wash it away.
The knife breaks open tiny cells
An onion stores two substances in separate compartments of its cells. When you cut it, the cells burst and the two mix for the first time.
Share this stepA stinging gas floats up
The mix creates a sulfur-based gas, the onion’s defense against hungry animals. It’s light and drifts straight up from the cutting board toward your face.
Share this stepYour eye feels the sting
When the gas meets the moisture on your eye, it forms a mild acid. Nerves in the eye sense the irritation and send an alarm to your brain.
Share this stepTears wash it away
Your brain tells the tear glands to flood the eye. The tears dilute and rinse away the irritant. Annoying, but it’s your eyes protecting themselves.
Share this stepTears are your eyes’ rinse cycle.
Cut cellsgastears
A sharp knife crushes fewer cells and releases less gas. Chilling the onion for 30 minutes slows the reaction, and cutting near a fan or open window blows the gas away.
Common follow-up questions
Does chewing gum or holding bread in your mouth help?
Not really. Some people breathe through their mouth more, which may help a little, but the gas reaches your eyes either way.
Why do some onions make you cry more than others?
Strong yellow and red onions contain more of the sulfur compounds. Sweet onions and green onions contain less and sting much less.
Does cooking stop the tears?
Yes. Heat breaks down the enzyme that creates the gas, which is why cooked onions don’t sting and taste sweeter.
Is the gas harmful?
No. It’s irritating but harmless, and the stinging fades within minutes.
