Cut an onion and your eyes may start to burn and tears may run down your face. Scientists have been investigating why this happens for decades. Now some researchers have uncovered a new piece of the complex answer. They have figured out how one of the veggie’s eye-irritating compounds forms.
When you slice an Onion, you unleash a chain of chemical reactions. Stable molecules in the onion’s tissues transform into a volatile, sulfur-containing gas. This gas reacts with the eyes to form small amounts of sulfuric acid. Sulfuric acid can lead to itching, burning – and tears.
The chemicals that hurt human eyes might also trigger pain in other organisms. This would make the plant less appealing to wildlife, insects and even some bacteria or fungi.
So this is why you are tearing while you were chopping the onion…