Onions belong to the Allium genus of flowering plants, which also includes garlic, leeks, shallots, scallions, and chives -- all of which absorb sulfur from the soil. When you cut into an onion, you break into its cells, releasing their contents. This action allows enzymes and amino acid sulfoxides from the cells to interact, producing a volatile sulfur gas. When those vapors mix with the water in your tears, sulfuric acid is created. The stinging sensation that results stimulates your eyes to release more tears, in order to try to wash away the irritant.
How to win the crying game:
- Tired of onion tears? Cook the onion first to deactivate the enzymes. Putting an onion in the freezer for a few minutes can also slow down its chemical reactions.
- Other defensive maneuvers include wearing safety goggles (to keep the vapors away from your eyes) or turning on a fan to redirect the gases.
- In 2015, Japanese researchers discovered that they could reduce tears by bombarding onion bulbs with ions. Other scientists are trying to alter the onion’s genes to make the crying stop.