Scientific Study Debunks Onion Myths: Sharpness, Not Temperature, is Key to Tear-Free Chopping

The root cause of this uncomfortable phenomenon is not a mystical power of the onion, but rather a meticulously calibrated chemical defense mechanism. When the onion’s cell walls are ruptured by a knife, an enzyme called alliinase is released. This enzyme reacts with sulfur-containing amino acids, resulting in the creation of a powerful chemical compound known as Propanethial S-oxide, sometimes referred to as the lachrymatory factor. This highly volatile gas quickly wafts into the air and, crucially, makes contact with the moisture on the surface of the eye. Once dissolved in the eye's fluid, the compound undergoes a secondary chemical conversion, forming a trace amount of diluted sulfuric acid, a potent irritant that triggers the pain and subsequent reflexive production of tears intended to wash the offending substance away.