Why Do We Cry When Cutting Onions? Discover the Chemistry, Tricks & Fun Facts – Știrinoi.com
- Jul 7
- 2 min read
Ever started chopping an onion and suddenly your eyes sting, stream tears, and you feel like heading out of the kitchen? At Știrinoi.com, we’ve delved into this everyday mystery: why onions make us cry, what happens chemically, and how we can avoid becoming teary chefs.
1. The Science Behind the Tears
Onions contain sulfur-rich compounds and enzymes (alliinases). When cells are broken, these combine to form syn‑propanethial S‑oxide — a volatile gas that irritates our eyes. Tears flood in as a defense to wash away the irritant . Britannica confirms the brain triggers a tear response to protect the eyes , and All About Vision explains the gas stimulates corneal nerves to trigger tearing .
2. Why Onions Use This Defense
This lachrymatory mechanism deters animals and pests underground. Sulfur compounds act as an invisible shield .
3. Why Some People Cry More
Variations in sensitivity — people with dry eyes, allergies, or contact lenses may cry more. One tester noted, “Wearing contact lenses… only mildly irritated my eyes,” whereas without them, tears flowed freely .
4. Fun Facts & Varieties
Sweet onions (Vidalia, Sunions) contain lower levels of lachrymatory enzymes .
Ancient Chinese from the Song dynasty used ginger and jujube to prevent tears .
GMO-free “tear‑free” Sunions were developed by silencing the LFS enzyme .
5. How to Chop Onions Without Tears
Effective methods:
Chill onions (fridge/freezer) to reduce gas release .
Use a sharp knife to minimize cell rupture.
Chop under running water or with a nearby stream to dilute gas .
Improve ventilation with a fan or hood to disperse gases .
Wear protective eyewear or use contacts/glasses as barriers .
Place a damp towel as a “magnet” for sulfur compounds .
Add acid (lemon or vinegar) to deactivate enzymes .
6. Opinions & Professional Tips
Chefs emphasize sharp knives and ventilation: “most practical solution without altering flavor” .
Eye specialists recommend goggles or contact lenses for eye protection .
TikTok doctors, like Dr. Joe Whittington, support the damp towel trick—results vary .
Conclusion
The next time you cry chopping onions, you can blame syn‑propanethial‑S‑oxide — your eyes' unexpected nemesis!
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