Why Do Onions Make You Cry

Why do onions make you cry?  Even the strongest of men cannot hold back the tears when faced with the mighty onion. Unfortunately, onions are encountered frequently as ingredients in so many of our favorite dishes. Even the most basic cook has cause to brave the dreaded onion in the kitchen. Why do onions make the eyes water—and what can you do to prevent tears when chopping onions?

What is in an onion to make you cry?  Onions are built by nature to fight off predators. While we know that onions taste great—we must first get past their “survival” mechanism:  the ability to make a grown man—or a young woman or little boy, etc. cry like a baby. Onions contain layers of cells divided by membranes. Some layers hold an enzyme that loves to combine with sulfur based chemicals on the other side of the membrane to form an air and water soluble sulfur based irritant. This irritant protects the onion underground from insects and other predators underground. One bite and the dining insect is repelled.

Why do your eyes tear up when cutting onions?  Okay, cutting an onion produces a sulfur based irritant. What does that have to do with human tears?  Once the sulfur irritant becomes airborne—or the onion cutter unwittingly wipes a bit of onion juice into the eye—the irritant from the onion reacts with the water in the human eye—creating a compound similar to sulfuric acid on the eye’s surface. The human eye goes into defense mode. It must relieve itself of the irritating chemical emitted from the onion. The eye’s best defense is to produce more water or tears to bathe the eye and soothe it from the burn of the irritant from the onion. Tears begin to flow.

How can you avoid crying when you chop onions? 

  • Cut onions under running water.  The chemicals present in onions are water soluble as well as air soluble—which means that if you cut the onion under running water, the chemicals will dissolve into the water first without going airborne and reaching the water in your eye.
  • Freezing the onion make it less able to make you cry. The decreased temperature slows down the reaction rate of the enzyme and its substrate—making fewer sulfur molecules ready to reach your eye.
  • Choose a lower sulfur onion. If you want fewer sulfur based irritants released, begin with a lower sulfur onion. Onions grown in lower, sulfur soil, such as Vidalia onions from Texas or Georgia, are “milder” onions than some other varieties–or even similar varieties from other locations of the country.
  • Leave the root end intact while chopping. Whether you believe it’s scientific or simply an old wives tale, it seems that cutting from the stem end of an onion creates less emission of the onion’s tear producing capabilities.

How can you stop the tears caused by chopping onions?  Onion produced tears have begun–what can you do to stop the tear filled response? The reaction is fairly short lived and should stop in a few minutes without any intervention on your part. Having a cool, damp kitchen towel available to dab onto the eyes helps stop the irritation when onions make you cry—making a short lived tear session.

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