The nitty-gritty behind how onions make you cry
(PHYSorg.com Chemistry)

Adding onions to a recipe can make a meal taste rich and savory, but cutting up the onion can be brutal.  Onions release a compound called lachrymatory factor (LF), which makes the eyes sting and water. Scientists know that a certain enzyme causes this irritating compound to form but precisely how it helps LF form in the onion remained an open question. Now, one group reports in ACS Chemical Biology that they have the answer.