If you’ve ever chopped an onion, you’ve probably experienced that familiar stinging sensation in your eyes, followed by tears. But why do onions make us cry? Here’s a simple explanation based on the science behind this everyday phenomenon.
The Culprit: Sulfur Compounds
Onions contain natural sulfur compounds. When you cut into an onion, you break its cells, releasing these sulfur compounds. One of the key compounds released is called syn-Propanethial-S-oxide. This compound is what ultimately makes your eyes water.
The Chemical Reaction
Here’s what happens step by step:
- Cutting the Onion: When you slice through an onion, you damage its cells, releasing enzymes called alliinases.
- Formation of Sulfenic Acid: These enzymes react with the sulfur compounds to form sulfenic acids.
- Formation of syn-Propanethial-S-oxide: The sulfenic acids quickly rearrange themselves into a volatile compound called syn-Propanethial-S-oxide.
- Release into the Air: This compound vaporizes and wafts through the air, eventually reaching your eyes.
The Eye’s Response
When syn-Propanethial-S-oxide reaches your eyes, it dissolves in the water present on the surface of your eyes, forming a mild sulfuric acid. This acid irritates the eyes, triggering a defensive response from your body.
- Tear Production: Your tear glands produce tears to wash away the irritant. This is why your eyes start to water.
- Stinging Sensation: The sulfuric acid also stimulates the nerves in your eyes, causing a stinging or burning sensation.
How to Minimize the Tears
There are a few tricks to reduce the tears when chopping onions:
- Chill the Onion: Cooling the onion before cutting it can slow down the release of the sulfur compounds.
- Cut Under Water: Cutting onions under running water or submerged in water can help as the water can dissolve the sulfur compounds before they reach your eyes.
- Ventilation: Ensure proper ventilation by using a fan or cutting onions near an open window to disperse the sulfur compounds.
Conclusion
While onions can be a bit of a tear-jerker, understanding the science behind why they make us cry can help us find ways to minimize the discomfort. The key player is syn-Propanethial-S-oxide, a sulfur compound released when onions are cut. This compound causes a mild acid to form in our eyes, triggering tears as a natural defense mechanism. So next time you chop an onion, remember these tips and tricks to keep the tears at bay!