Cutting onions often leads to tearing up due to the release of a gas called syn-propanethial-S-oxide when the onion cells are damaged. To reduce tears, you can try chilling the onion in the refrigerator before cutting, which slows down the release of the gas. You can also cut onions under running water or wear goggles to shield your eyes. Using a sharp knife and ensuring proper ventilation in the kitchen can also help minimize the tear-inducing effects.