https://www.theregister.co.uk/2017/08/03/onion_cutting_study/ >We’re all familiar with the burning, eye-watering sensation felt when chopping onions, and now we know exactly why. >The US National Onion Association estimates that the average American chows through about nine kilograms (20 pounds) of onions every year – that’s a lot of tears. We know that a lachrymatory factor (LF) agent causes us to burst into tears, and this is presumably produced by the onion as a natural defense mechanism to deter us from biting into the vegetable's crunchy flesh.