WHAT IS IT ABOUT ONIONS THAT MAKES US CRY?

Slicing through an onion breaks open a number of cells, which releases enzymes. The escaped enzymes, allinase and lachrymatoryfactor synthase, decompose some of the other released substances, called amino acid sulfoxides. This reaction forms unstable sulfenic acids, which stabilize into a volatile gas. When this gas reaches our eyes, it reacts with the water that is intended to keep our eyes moist. The sulfenic acids mix with the tears in our eyes to form sulfuric acid, which is the same toxic stuff that is in our car batteries. Never ending in our eyes pick up this irritant and send a message to the brain, which then passes a message to our tear ducts to protect the eyes. So crying or tearing is a protective measure.

The best way to deal with this phenomenon is to move away from the sliced onion instead of standing directly over it. There are also some techniques in the kitchen that you can employ. You can cook the onion first, before slicing it; the cooking process inactivates some of the enzymes. You can refrigerate it first. You can wear contact lenses or goggles. You can use a fan to blow away the fumes. You can slice the onion while running tap water over it or cut it underwater, because the water will react with some of the released gas before it reaches your eyes. Steam from a kettle will also do the trick.