Why Do Onions Make You Cry

When you cut an onion, your eyes start to sting and water. This happens because onions release a special gas when they are cut. The gas floats up to your eyes and irritates them. Your eyes make tears to wash the irritating gas away.

The Chemistry of Onion Tears

Onions contain sulfur compounds. When you cut an onion, you break open its cells. The compounds mix together and form a gas called syn-propanethial-S-oxide. This gas floats up into the air and reaches your eyes. It reacts with the water in your eyes to form a mild acid. Your eyes sting, so they make tears to flush it out.

How to Stop the Tears

There are some tricks to cut onions without crying. Chilling the onion in the refrigerator before cutting slows down the chemical reaction. Cutting the onion under running water washes away the gas. Wearing goggles keeps the gas out of your eyes. Some people even light a candle nearby to burn up the gas.

Fun Facts

• Scientists in Japan have created a tearless onion by removing the gene that produces the irritating gas.
• Sweet onions like Vidalia onions have fewer sulfur compounds and cause less crying.
• Onions have been eaten by humans for over 5,000 years.

Did You Know?

The reason onions make the irritating gas is probably to protect themselves from animals that want to eat them. The strong smell and eye-stinging chemicals are the onion's defense system!