Why are you crying over the onion?
You happily cut onions for dinner, when BAM! Your eyes pinch, and tears run down your face. Maybe the burning is that strong, that you need to step back! Why is onion such an unpleasant vegetable sometimes? Well, it actually comes down to a fascinating biochemistry. Before it was in your kitchen, the onion happily produced food from the sun and absorbed minerals from the soil. It turns out, that onions are particularly good at absorbing sulfur, which it uses in many amino acids. When you cut the onion, you open cell by cell, releasing their liquid contents. Previously separated enzymes meet sulfur-rich amino acids and form unstable sulfenic acids, which then turns into a chemical known as syn-propanetial-S-oxide. This insidious chemical is volatile, which means, that it evaporates easily and causes a burning sensation, when it rises from the cutting board and comes into contact with the eyeballs. Trying to protect your precious eyes from damage, the brain quickly releases a tear, to flush out the irritant. You are left with red eyes and tear stained cheeks in the center of the kitchen, obvious victim of some sort (amazing) botanical war.
So what can be done, to reduce all this onion chemistry drama? Some varieties of onions, especially sweet onions, they are less sulfuric than others and therefore less prone to watery eyes. You can also freeze or cool the onion, before you cut it; this slows down the enzymes responsible for a series of unfortunate chemical events. Other tricks – such as lighting a match, eating bread while chopping or breathing with your mouth – they are much less effective (if they are at all), but desperation is the mother of invention (or something like that), truth? Try them out, if you must.