This is the real reason onions make you cry

Do you have a bad reaction to chopping onions?

Do you have a bad reaction to chopping onions?
Unsplash / Caroline Attwood

Onions are a staple of many dishes, but we use it at a cost. When chopping them up, many of us feel our eyes start to sting, then we start crying.

There are plenty of old wives’ tales about how to stop the tears, from putting a piece of bread under your nose, to only using fresh onions. But what is it about onions that makes us react this way?

According to an article in The Conversation, all vegetables release chemicals called polyphenols when they are damaged and their cells are ripped open. It’s a way of the plant defending itself from hungry animals and pests.

Onions have a particularly irritating chemical called propanthial s-oxide, which is very volatile. This means it quickly evaporates when it’s released, and makes its way into our eyes.

In your eyes, the chemical mixes with water to create sulphenic acid, which irritates the tear glands. It’s only a tiny amount of acid produced, so it’s not harmful, but it’s enough to make us cry.

There is some debate about why onions have this special power. It could be because there are higher levels of sulphur in the soil onions grow in.

The Conversation article says sweeter onions tend to have less of the compounds that produce the chemicals, but really there’s no way to tell if an onion will make you cry until you cut into it.

If you’re particularly affected by the onion’s chemicals, you could try buying some goggles, boiling the onions before cutting them – although this isn’t advisable – or just get someone who isn’t so easily affected to cut them up for you.