Why Do Onions Make Us Cry and Leave a Lasting Impression on Our Taste Buds?

Onions are the often overlooked ingredient in our favorite dishes. They add depth and flavor to soups, stews, and sauces, but have you ever stopped to think about why they make our eyes water and leave a lingering taste in our mouths?

Let’s dive into the science behind the strong taste and aroma of onions.

The Chemistry of Onions

When an onion is cut or chopped, an enzyme called alliinase is released. This enzyme then reacts with a sulfur compound called sulfoxides, creating a new compound called syn-propanethial-S-oxide.

This compound is responsible for the strong smell and taste of onions.

But why do onions contain these compounds in the first place? Onions, like other members of the Allium family (garlic, leeks, chives, etc.), contain these compounds as a defense mechanism against animals and insects that may try to eat them. The strong smell and taste act as a deterrent, protecting the onion from being devoured.

Why Do Onions Make Us Cry?

As the alliinase and sulfoxides react, they also release another compound called lachrymatory-factor synthase (LFS). LFS is what causes the tears to flow when cutting or chopping onions.

The compound is released into the air and when it comes into contact with the moisture in our eyes, it creates a mild acid. This acid then irritates the eyes, causing them to tear up as a way to flush out the irritant.

How to Minimize the Tear-Inducing Effects of Onions

  • Chill the onions before cutting them. Cold temperatures slow down the chemical reaction that releases LFS, resulting in fewer tears.
  • Cut the onions under running water or use a fan to blow the LFS away from your face.
  • Use a sharp knife to make precise cuts. Smashing or crushing the onions releases more LFS into the air.
  • Peel the onions under water to avoid the release of LFS in the air.

How to Enhance the Flavor of Onions

Now that we understand the science behind the strong taste and aroma of onions, let’s talk about how to enhance their flavor.

  • Roast them: Roasting onions brings out their natural sweetness and mellows out their sharpness.
  • Caramelize them: Slowly cooking onions over low heat until they turn a deep brown color brings out their natural sugars and enhances their flavor.
  • Pickle them: Pickling onions in vinegar or brine solution infuses them with new flavors and makes them less pungent.


Onions may make us cry and leave a lasting impression on our taste buds, but their strong taste and aroma are what make them so versatile in cooking.

The next time you chop an onion, take a moment to appreciate the science behind its flavor. And don’t forget to keep a box of tissues nearby!