Why do onions make you cry?

pourquoi les oignons font-ils pleurer

You never forget the first time you peel an onion. Actually, our eyes remember it, and for good reason. It itches and our eyes cry without the onions touching our face. Strange isn’t it?

Onions make you cry because they contain tear-inducing gas.

Onions, like shallots and garlic, have the power to make us cry when we peel them. These plants which belong to the same family of Liliaceae grow in the ground. During this stage, the onion is enriched with sulfur compounds which belong to the family of tear-inducing gas.


This says of a compound that attacks, that eats away at materials.


There are weak acids that have a bitter taste like lemon juice, and strong acids, which are toxic, like sulfuric acid, which are used in car batteries. In all cases, chemists define acids as molecules capable of losing a H+ proton in water.

The cause of our tears is propanethial oxide. A gas released into the air the minute you slice the onion. This gas comes into contact with our eyes. But as our eyes are wet, this gas will turn into a very powerful acid called sulfuric acid.

Sulfuric acid is a compound to be handled with great care in companies because it is corrosive.


Why do we cry in the presence of tear gas?

It’s a protection that mother nature has given to us. To protect our eyes, nature has provided us with glands called the lacrimal glands. They are the ones that form tears and provide good moisture for our eyes.

When our eyes are attacked by something acidic, or simply by dust, the tear glands produce tears to clean them. This is what happens with onions, the tear glands produce tears to get rid of the sulfuric acid produced on contact with our eyes.

Is there any trick to prevent us from crying when we peel the onions?


According to the National Onion Association located in the state of Colorado in the United States of America, there are a few tips to reduce tear production when cut. The trick is to let the onion cool for at least 30 minutes. Then, just remove the top when peeling it. In fact, the other end with the root is the part richest in sulfur compounds.