Chopping onions often leave tears rolling down our cheeks. We shed tears because our eyes are irritated by droplets the onion releases when we chop them.
It turns out when you cut an onion, it releases a gas called Propane thiol, S-oxide. When mixed with certain enzymes in the onion, it creates a sulfur gas.
These gases then get to your eyes and create a mild acid which irritates the eyes.
However, rubbing your eyes is a bad idea, since your hands are likely full of the tear making onion juice. The eyes tear up to protect themselves.
Here is how to cut onions without shedding tears:
1. Cut while chewing gum
Sounds fancy, right? Well, it works magic! The theory is that having something in your mouth encourages you to breathe through your mouth, sucking in the droplets before they hit your eyes.
2. Freeze the Onion
Put the onion in the freezer for about 5 minutes before cutting it. However, it will be a little tougher to cut (owing to the fact that it is partially frozen) and it will be difficult to remove the papery, outermost layer.
The theory with this one is the cold inhibits the onions’ release of its eye-irritating chemicals.
3. Chop with a very sharp, stainless steel knife.
Chop with a very sharp, stainless steel knife that has been run under water before starting to slice. If cutting a lot of onions or even a single large one, run knife frequently under water. The water will help absorb the sulfur compounds and a sharp knife will make a cleaner cut, bruising the onion cells less which theoretically means causing less reaction. Stainless steel is thought by some to attract the sulfur compounds. 4. Light a candle nearby It is believed that the flame will take away some of the onion fumes that cause tears. Cut onions as close to the flame as possible without danger of being burned. The heat will draw the sulfur to it and away from your eyes.
5. Cut the onion underwater.
Though this is certainly one of the less safe options, cutting an onion under water will prevent the sulfuric compounds from reaching your eyes and causing you to tear. However, an alternative to this is to cut the onion into two equal parts and deep/soak them in water for about 5 minutes before chopping.