Why do onions make people cry when they cut them?

When you cut into an onion, you damage its cells, releasing a gas called syn-propanethial-S-oxide (SPSO). This gas diffuses through the air and reacts with the water in your eyes to produce sulfuric acid. Sulfuric acid is a strong irritant, which causes your eyes to burn and water.

The amount of SPSO released depends on the type of onion and how it is cut. Red onions typically produce more SPSO than other varieties, and cutting onions into small pieces releases more gas.

There are a few things you can do to reduce the amount of tears you shed when cutting onions:

* Choose a mild variety of onion, such as a yellow or white onion.

* Cut the onion under cold running water.

* Use a sharp knife to make clean, even cuts.

* Wear goggles or glasses to protect your eyes.

If you do get tears in your eyes, rinse them with cool water and apply a cold compress to reduce swelling.