We don't cry when cutting onions. This is not crying, for no emotion is involved. Onions produce a chemical irritant that stimulates the lachrymal glands and tears are produced. It is cutting or smashing into onions that cause two otherwise separate elements to combine and produce the irritant. It is the vegetable's way of defending itself, producing something bitter or repellant so that it will not be attacked.
Apparently, the soil the onions grow in may affect the degree of irritation to the eyes. Soils highly rich in sulphur seem to bring forth onions which cause more of a problem than others. In any case the irritation is not damaging, and only temporary. Soaking the onion in the water for a few minutes before cutting should decrease the irritants effect.
