The chemical at the heart of our discomfort is called propanethial S-oxide, which is also known as lachrymatory factor (LF). The technical term for our tear glands is “lacrimal glands,” and LF is a chemical that causes tears.
When we start chopping, the cells inside the onion are broken up. As a consequence, an enzyme called alliinase is released, which produces the chemicals that are subsequently broken down into flavor molecules. These give onions their characteristic taste.
Some of the chemicals involved in this reaction are turned into LF by LF synthase. When LF comes into contact with the front of the eye, or the cornea, nerve endings located here signal to the brain that an irritant has arrived on the scene. This, in turn, leads to signaling back from the brain to the tear glands.
Wear safety glasses if you don’t want to tear up while slicing an onion. You’ll look a little silly, but that beats looking like a crybaby.
Picture Credit : Google