Onions make cooks cry because cutting them releases a volatile sulfur compound that irritates eyes.

The longer version

Cutting into an onion ruptures cells and lets previously separated enzymes mix with sulfur-bearing molecules stored elsewhere in the cell. The reaction produces a volatile compound that drifts upward, and when it dissolves in the water film covering the eye it forms a mild acid that stimulates nerve endings. The body responds by flooding the area with tears.

The compound forms quickly and disperses, which is why the effect fades. Lower temperatures slow the release because volatility drops, and a sharper blade damages fewer cells than a dull one. Similar sulfur chemistry gives the vegetable its pungent raw taste.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.