Why do onions make you cry?

A whole onion contains no tear gas at all. It builds it in the instant your knife breaks its cells, and the vapour heads straight for the most nerve-packed surface in your body: your eyes. Follow one molecule from the cutting board to your tears. See how two ingredients kept apart in every onion cell meet when you cut, why a second enzyme discovered in 2002 decides between tears and flavour, how your cornea and brainstem trigger reflex tears, why garlic rarely makes you cry, and which kitchen tricks are backed by evidence and which are myths. Cells, molecules and the eye are illustrative and not to scale; the vapour is drawn in green but is invisible in real life. The exact eye sensors involved are still being studied, and tips like chilling the onion are not fully settled. Which everyday kitchen mystery should we explain next? Tell us in the comments and subscribe for more everyday science. #Onions #KitchenScience #Exploriny