why do you cry when you cut onions

Cutting onions makes you cry because breaking the onion’s cells triggers a chemical reaction that releases a volatile irritant into the air, and that irritant stings your eyes and makes them produce tears.

Quick Scoop

When an onion is intact, its chemicals are kept separate. Once you slice into it, those compartments break open, enzymes react with sulfur-containing compounds, and a tear-causing gas forms.

What Happens

• Cutting the onion ruptures its cells and mixes compounds that were previously isolated.

• That reaction produces syn-propanethial-S-oxide, the irritant that reaches your eyes.

• Your eyes detect the irritant and respond by making tears to flush it out.

Why It Burns

The gas is volatile, so it moves quickly through the air and gets to your eyes fast. Once it touches the eye’s surface, it irritates the nerves and triggers the watering reflex.

How To Cry Less

• Use a sharp knife, because dull blades crush more cells and release more irritant.

• Cut gently instead of smashing the onion.

• Ventilate the area or stand a little farther away so the gas disperses.

• Some people also use goggles or chill onions, though chilling can have mixed results depending on the source.

In short, onion tears are your body’s defense reflex responding to a plant’s own defense chemistry.