Food · Thursday, October 15, 2026
Why Do Onions Make You Cry? The Chemistry Behind Tears
Discover the fascinating science behind why cutting onions makes you cry, plus practical, chef-approved tips to stop the tears for good.
The Chemistry of the Cry
We have all been there: you are simply trying to chop an onion for a weeknight dinner, and suddenly your eyes are stinging, watering, and streaming as if you are watching a tragic movie. It is one of the most universally shared culinary experiences, but why does it happen? The answer lies in a clever defense mechanism developed by the onion over millions of years of evolution.
Onions are root vegetables that absorb sulfur from the soil as they grow. When you slice into an onion, you rupture its cellular walls. This mechanical damage brings together two things that are normally kept strictly apart inside the plant: enzymes called alliinases and sulfur-containing amino acid sulfoxides. Once these two components mix, a rapid chemical reaction takes place, creating volatile sulfur compounds that escape into the air.
From Gas to Tears
As those volatile compounds waft upward from your cutting board and reach your face, they react with the moisture on the surface of your eyeballs. Specifically, they dissolve in the tear film that protects your eyes, forming a mild solution of sulfuric acid.
This tiny bit of acid causes a mild irritation to your eyes. Your lacrimal glands—the tear ducts responsible for keeping your eyes lubricated—instantly go into overdrive to flush out the irritant. Essentially, your body is crying to wash away the chemical intruder, which is why the tears flow so profusely the moment you start chopping.
Why Do Some Onions Hurt More Than Others?
Have you ever noticed that a sweet Vidalia onion barely makes your eyes water, while a sharp yellow or red onion has you weeping within seconds? The intensity of the tear-jerk reaction depends heavily on the growing conditions of the onion and its sulfur content.
Onions grown in soil that is rich in sulfur tend to produce much stronger chemical reactions when sliced. Furthermore, variety matters: pungent storage onions have higher concentrations of the precursor molecules that create the crying gas, while milder, sweeter varieties grown in specific climates have far fewer. Temperature and storage also play a role; onions kept in warmer, more humid environments can sometimes behave more aggressively when cut.
Chef-Approved Ways to Beat the Tears
Since we cannot change the fundamental chemistry of Allium cepa, how can home cooks protect their eyes? The most effective strategy is to slow down the chemical reaction before it reaches your face. Chilling your onion in the refrigerator for about 30 minutes before cutting is a classic trick. Cold temperatures slow down the enzymatic activity, meaning fewer volatile gases are released into the air.
Another great method is upgrading your kitchen tools. A dull knife crushes and bruises the onion cells, releasing a massive amount of juice and gas into the air. A razor-sharp chef’s knife slices cleanly through the cells, drastically reducing the amount of chemical spray that makes it up to your eyes. Finally, cutting onions near a running kitchen fan or an open window can easily blow the gases away from your face entirely.
Frequently asked questions
Do onion goggles actually work?
Yes! Specialty onion goggles seal tightly around your eyes, creating a physical barrier that prevents the airborne sulfur compounds from reaching your tear film.
Does chewing gum stop you from crying while cutting onions?
Chewing gum or breathing through your mouth can help slightly by encouraging you to draw air inward, but it is not nearly as effective as chilling the onion or using a sharp knife.
Why do white onions make you cry?
White, yellow, and red onions contain high levels of sulfur compounds absorbed from the soil, which react with enzymes when sliced to create the tear-inducing gas.
Written by the DailyTwist editorial team for general information. Spotted an error? Tell us.
