Murray’s 60sec science of the day ….. a little less philosophical then previous
Why do onions make you cry?
Inside onion cells are chemical compounds that contain sulfur. When you cut into an onion you break the cell wall and these compounds can react with the atmosphere releasing sulfur-based gases. These gases, in turn, react with the moisture in your eye creating sulfuric acid. This is the burning sensation. Your brain responds instructing the tear ducts to create more moisture to dilute the acid and protect your eyes.
Rubbing your eyes with your hands could make it worse as the sulfur will react with the moisture in your hands making more sulfuric acid which is then added to the eyes.
A suggestion is to cut the onions under water to dissolve the gasses as they are released (then you can test the pH of the water to see what’s happened) OR cool the onion down in a freezer (for about 10mins) to slow the reaction rate so less will reach your eyes.