How to Not Cry Cutting an Onion
Shanthi Appelo, MS, RD
| 3 min read
Let’s be honest – no one likes to cry over an onion. You start out feeling like a confident home chef, and three slices later, you’re wiping tears away, questioning life choices and blaming the onion for emotional damage.
The science
But there’s good news: the problem isn’t you – it’s chemistry. When an onion “fights back,” it’s just defending itself with an eye irritant. The plant evolved a chemical defense where damaged cells release enzymes that convert onion sulfur compounds into syn-propanethial-S-oxide. This volatile molecule that reaches your eyes, reacts with the water in your tear film and produces the stinging sensation that triggers reflex tears.
How to reduce tearing
You don’t need to suffer through the onion tears. Let’s break down a few science-backed ways to disarm the onion’s defense and look at a few other methods with mixed evidence:
- Use a sharp knife. A sharp knife slices cleanly instead of crushing the onion cells, which means fewer irritant gases are released, according to a 2025 Cornell University Study. The study found duller blades produced nearly 40 times more particles than their sharp counterparts.
- Keep the root intact. According to the National Onion Association, the root end has the highest concentration of tear-triggering compounds. It’s best to cut off the stem, peel the outer skin and cut the onion lengthwise, then carefully cut avoiding the root.
- Cut slowly and deliberately. Avoid hacking quickly, which can force more aerosols out. Using slow and deliberate may reduce the number of tiny droplets ejected by four times.
- Wear a physical barrier. Wearing sealed pair of goggles like ski or lab goggles prevents the volatile compounds from reaching the eye surface entirely. The American Academy of Ophthalmology recommends eye protection for sensitive individuals. Wearing contact lenses also creates a barrier between the eyes and the onion particles, but it’s a good idea to clean them afterwards.
- Position yourself near ventilation. Cut near a fan, under a kitchen hood or near an open window so the irritant is carried away from your face. Recent imaging studies show onions can eject aerosols a fair distance, so moving air prevents them from lingering near your eyes.
- Chill the onion. Chilling an onion for 30-60 minutes before cutting has mixed evidence. The theory is that chilling can reduce enzyme activity and thereby production of the irritant. While this may be the case, a recent study found onions that had been chilled for 12 hours increased the number of droplets released compared to room temperature.
- Coating with oil. This method is experimental but promising. Laboratory work and reporting on aerosol behavior suggest a thin oil coating on the knife can trap volatile droplets and cut down on how much reaches the air.
- Tear-free onions. Plant scientists have bred “no-cry” onions like Sunions and Smileys, which naturally produce less of the tear-inducing enzyme. However, due to their lower levels of these compounds, they may have a less powerful taste than their feisty counterparts. Their higher water content can also make them more perishable.
In short, use a sharp knife, cut slowly leaving the root intact around good airflow. Try coating the knife in some cooking oil to see if it works for you. If you want guaranteed comfort, throw on some goggles.
Photo credit: Getty Images
