Why do onions make us cry?

It is not the strong smell that makes us cry, but the gas that the onions release when we cut them. When this gas meets the water in our eyes it produces sulphuric acid which irritates our noses and eyes. One good tip, therefore, is to use a sharp knife as this will crush the onion less and reduce the amount of gas released. Another good idea is to cut the root of the onion last or not at all, since this part produces the highest levels of offending gas. Other less logical-sounding suggestions, which many people swear by, include putting the onion in the freezer for twenty minutes beforehand, having a bowl of water or a burning candle alongside while you chop, or putting a piece of bread in your mouth. The less self-conscious among us even keep a pair of swimming goggles handy for onion-chopping.