Why Onions Make You Cry: A Chemistry Breakdown

Onions store sulfur compounds in their cells, harmless until the onion is cut.
Cutting an onion breaks cells open, releasing enzymes called alliinases.
These enzymes react with sulfur compounds to form volatile gases.
The key irritant is syn-Propanethial-S-oxide, a chemical that makes eyes water.
Tears are a defense, as your eyes try to wash away the irritating gas.
Chilling onions slows enzyme activity, reducing how much irritant forms.
Sharp knives cause less damage to cells, releasing fewer tear-inducing compounds.
Cooking onions destroys the enzymes, which is why sautéed onions don’t make you cry.
Goggles work by blocking the gases from reaching your eyes.
Different onion varieties contain varying sulfur levels, so some sting more than others.