Why do onions make you cry?

Why do onions make you cry?:

When you cut into an onion, you slice through cells which contain sulfur compounds. Sulfur is quite a noxious (bad smelling) element. The compounds released are highly volatile, meaning they quickly enter the air in their vicinity. Your eyes produce tears because your body wants to wash or dilute the chemicals before they effect your eyes. The tears are a natural way the body can wash the offensive chemicals away.