Why Does Chopping Onions Drive Us to Tears?

Tears and a runny nose? Looks like that recipe called for freshly chopped onion! What is it about onions that sends our tear ducts into overdrive?

Onions are Full of Sulfur

As onions grow, they absorb sulfur from the soil. Onions also contain special enzymes that lie in reserve ready to break down those sulfurous molecules. The sulfurous molecules and enzymes remain separated until that first chop, when the sulfur and enzymes combine in a reaction that creates sulfenic acid. This acid quickly evaporates into a gas, which wafts up into our eyes.

The Science

Our Eyes Tear Up to Protect Themselves

Our eyes produces three types of tears—emotional, basal, and reflexive. We all know the basis of emotional tears are. Basal tears account for the constant moisture protecting and lubricating our eyes. Onions trigger reflexive tears, an automatic defense mechanism. When acidic vapors reach our eyes, our brain interprets it as a burning sensation and tears spike to wash out the irritant.

Some Tips To Minimize The Tears

Next time you cook with onion, try these tips to keep your eyes clear as you cook that amazing meal:

• Refrigerate the onion before you cut it, suppressing chemical reactions
• Wear eye protection like a pair of goggles
• Cut the onion under water
• Chop near a vent, or a pot of boiling water, which can dissipate the irritating gas
• Use a sharper knife. Cutting instead of crushing releases less vapor.
• Learn to cut the onion quicker minimizing exposure time (see video below).

Chop Like A Pro To Minimize Tear Time!

Our Eyes Have Amazing Defenses

The more people know about their eyes, the more they respect the incredible things eyes can do. In each of our Vision Source practices, it’s always our goal to help protect your vision by providing the best diagnosis, treatment, and preventive care.

To find a Vision Source eye doctor near you, click here. 

Top image by Flickr user Sjaak used under Creative Commons Attribution-Sharealike 4.0 license. Image cropped and modified from original.