Why do onions make us cry?

Onions contain amino acid sulfoxides.which Means That when the onion is sliced it turns into a gas. The gas reaches your eyes and reacts with Tears. The gas then becomes a mild sulfuric acid, which irritates the eyes. To Prevent teary eyes While Cutting an onion :
1) Put the onions in the freezer for a couple of minutes before you cut them.

2) Break off a piece of bread, hold it between your teeth, and breathe through your mouth.

3) Wear swimming goggles.