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Why Do I Cry While Chopping Onions? Here’s The Not-So-Emotional Truth

May 3, 2022 | Eye Health | 0 comments

Onions go great in a lot of things: burgers, salads, chicken pasta…but when you're chopping them, they can make you cry.

It’s no secret that slicing onions as you prepare your tasty dinner can evoke tears within seconds. But unless you have a strong connection with your vegetables, most people aren’t overly emotional about their onions; there must be something else going on to cause those lids to well up.

The burning sensation is obvious enough once you start cutting onions, and might even feel akin to the symptoms of Dry Eye Syndrome. Are the fumes from chopped onions something to be careful about? Are onions hurting your eyes when they make you cry? Let’s peel the layers off this mystery!

Why Do Onions Make You Cry?

What exactly is in an onion that makes you tear up, and how does it happen?

To understand the cause, we need to don our lab coats and get ready to delve into some chemistry science. Before you bought your onions at the store, they likely started their growth cycle below ground on a farm. While growing underground, onions tend to absorb sulfur from the soil around them to produce amino acids. This helps the plant create amino acid sulfoxides as a byproduct.

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Fast forward to your cutting board, and something interesting happens when you take the knife to that same onion: as you slice into it, you’re actually cutting into its fibers and letting out the moisture built up inside. This allows enzymes to react with the stored amino acids, ultimately giving birth to a new compound called syn-propanethial-S-oxide. Due to the high volatility of S-oxide, it quickly evaporates into a gas and rises from the onion — right into your eyes!

Once S-oxide encounters your eyes, it mixes with your tears to form a mild sulfuric acid in your eyes. As you might guess, the surfaces of your eyes don’t take kindly to this and seek to retaliate to the burning sensation that soon follows. Your tear ducts then react by producing a high volume of moisture in hopes of flushing out the acidic mixture. Hence, your eyes water!

Are Onions Bad for Your Eyes When You Tear Up?

So then, is the process of crying while cutting onions truly bad for the health of your eyes?

In short, not at all. Although the feeling of onion aroma stinging your eyes isn’t pleasant, rest assured it isn’t doing any permanent harm to your ocular system. Your body is well-equipped to deal with foreign particles and compounds that find their way to your cornea through the air. Nevertheless, the painful burning from onions can certainly aggravate pre-existing dry eye symptoms, leading to quick flare-ups while your meal is in the works. There are a few options to avoid this problem.

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Try cutting your onion in a different way to prevent the stinging gases from escaping into the air in the first place. Cutting the vegetable under running sink water works well to keep S-oxide from posing a threat. You can also try using an onion cutter to get the dirty work done with minimal sulfur exposure. Lastly, being careful not to chop the root end of the onion can help protect you, as that’s where the bulk of the sulfuric compounds are usually stored.

If you tend to be onion-sensitive and tear up as soon as you see one, you can always resort to artificial tears to give your tear ducts the upper hand!

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