Chopping onions makes you cry because cutting into them triggers a tiny chemical attack on your eyes, and your tear glands respond by flushing the irritant away.

What happens when you cut an onion?

When you slice into an onion, you break its cells open and release enzymes and sulfur-containing compounds that were kept separate inside the bulb. These react to form a volatile gas called syn-Propanethial-S-oxide , often called the “lachrymatory factor” because it makes the eyes water.

How that gas makes you cry

The gas drifts up to your eyes and dissolves in the thin layer of moisture on the surface. This irritates nerves and the lachrymal (tear) glands, which then produce reflex tears to dilute and wash the irritant away, causing the classic onion‑chopping “crying” effect.

Why some onions (and people) are worse

Stronger, more pungent onions like many white or yellow varieties tend to produce more of the sulfur compounds, so they make more of the irritating gas. Some people are simply more sensitive to eye irritants, so even a small amount of the gas can make their eyes sting and water.

Ways to reduce the tears

People commonly try tricks to keep the gas away from their eyes or reduce how much forms in the first place. Popular approaches include:

  • Chilling the onion in the fridge or ice water before cutting to slow the chemical reaction.
  • Using a very sharp knife so you crush fewer cells and release fewer irritants.
  • Increasing ventilation, like cutting near a fan or open window, so the gas blows away from your face.
  • Wearing kitchen or safety goggles to physically block the gas from reaching your eyes.

Fun forum-style angle

Online discussions and forum threads often joke that “chopping humans makes onions cry,” playing on how universal this teary reaction is in home kitchens. At the same time, cooking communities trade practical onion‑cutting hacks, from special knives to candles and fans, even if not all of them work equally well in real life.

In short, onions are not making you “emotional” — it is just chemistry meeting your eye’s built‑in defense system.

Information gathered from public forums or data available on the internet and portrayed here.