Ever wonder why we start crying when chopping up onions?
Cells, which are irritating to the eye, are released from the vegetable when an onion is cut into. Onions are part of a plant family (same as garlic and chives) that absorbs sulfur in the earth, which forms a class of volatile organic molecules called amino acid sulfoxides. Sulfoxides are the cells released from the onion which are aggravating to the eye.
To read the full article: http://www.longislandeyedoctor.com/2015/01/onions-real-tear-jerker/