Onions contain amino acid sulfoxides, which when the onion is sliced turn into a gas. The gas reaches your eyes and reacts with your the natural tear lubricants. The gas then becomes a mild sulfuric acid, which irritates the eyes. To protect the eye, the tear ducts produce more tears to dilute the acid, which just makes it worse.
Some people think biting a slice of lemon or bread will keep you from crying when chopping an onion.
jimreinhold
2005-11-17 16:47:37 UTC
Another couple of suggestions to prevent onions from making you cry that I've come across:
1) Put the onions in the freezer for a couple of minutes before you cut them.
2) Break off a piece of bread, hold it between your teeth, and breathe through your mouth.
3) Wear swimming goggles.
The latter 2 might evoke intersting reactions from your dinner guests. Your mileage may vary with all three.
2005-11-09 18:57:59 UTC
Try this the next time you slice an onion--move your cutting board next to the sink and turn on the water--your eyes won't sting!
ⓘ
This content was originally posted on Y! Answers, a Q&A website that shut down in 2021.