Good question, and one to which there are a variety of tried-and-tested solutions, most of which don't involve buying specialist swim-wear, luckily!
These techniques include (though are probably not limited to) the following - some of which sound crazier than others:
- Wearing goggles, as someone else has already suggested
- Soaking the onion in water for 20 minutes before chopping
- Chopping close to a naked flame, either from a candle, or a lighted gas burner
- Holding a piece of white bread in your mouth while cutting
- Using an extremely-sharp knife and chopping as quickly as possible
- Using a fan to direct the air away from you
- Refrigerate the onion before use
I personally can't see any reason at all why the bread-in-the-mouth trick would work, and my sight's so poor that I'd pose a major hazard to myself and others if I wore goggles while wielding a sharp knife, especially if standing close to a naked flame at the same time!
My method of choice is therefore to use a very sharp, good quality chef's knife, then to chop as quickly as my knife skills will allow.
I also avoid cutting through the root of the onion until the last moment.
Finally, I get rid of the onion peelings as quickly as I can, as that also seems to help minimise the tears!
The reason why many of us cry when chopping onions is due to the acid vapour released by the onion once it's cut.
This gas is picked up by sensory cells in our eyes, leading the brain to send a signal to our lachrymal glands - which instructs them to release tears to wash the irritant substance away.
Onions absorb sulphur from the soil while they grow, which combines with the amino acids already present in their cells to form amino acid sulfoxides.
In 2002, Japanese research scientists discovered an enzyme, which unlocks these sulfoxides when an onion is cut, causing a reaction which then produces sulfenic acid.
The sulfenic acid then re-forms into a gas known as Syn-Propanethial-S-Oxide, which - when it hits the sensitive membranes of our eyes - causes them to sting and release tears.
For this reason, some scientists suggest freezing the onion prior to chopping it, as this serves to slow down the chemical reaction.
You can find out more about the chemistry of what happens when you chop an onion, in this video:
