Why Do Onions Make Us Cry?

You’ve probably experienced the burning and tearing in your eyes when you cut onions. But why do onions affect our eyes the way they do? What kinds of chemicals are in play?

Well, here it is.

When onions grow in the soil, they absorb many nutrients including sulfur. When an onion reaches our kitchen counter, it does not emit any gases and no matter how long we stare at the onion, we will not tear.

But when we cut into the onion, we break the cell membranes and allow the chemicals that are normally separated by their compartments to spill out and mix. Some of these chemicals include “amino acid sulfoxides” and various enzymes that carry important functions in the onions.

Now that these chemicals are free to mix, they create what is called “propanethiol S-oxide” which is a volatile sulfur gas. This gas floats into our watery lubricated eyes and creates sulfuric acid. Sulfuric acid (H2SO4) is one of the six strong acids of chemistry. Therefore, the sulfuric acid burns, stimulating our eyes to release more tears and to wash away the irritant.

So what can we do to minimize these uncomfortable side-effects?

1. By putting the onions in the freezer 30 minutes before cutting them, you will slow down the activity of the enzymes, therefore reducing the amount of volatile sulfur gas that is created.

2. By cooking the onions in hot water, you will denature the enzymes (inactivate them) and also reduce the amount of volatile sulfur gas that is created.

3. By putting goggles on, the volatile sulfur gas will not come in contact with your eyes, preventing any sulfuric acid from forming on your eyes.

Onion sufferers don’t worry, scientists are breeding a new strain of onions that have decreased levels of harmful enzymes so that tear-inducing onions could become a thing of the past.

What do you guys think? Do you like this? How about a question you would like me to answer for next week’s blog.

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