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.
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Our eyes produces three types of tears—emotional, basal, and reflexive. You know what emotional tears are. Basal tears account for the constant moisture protecting and lubricating. 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.
Next time you cook with onion, try these tips to keep your eyes clear as you cook that amazing meal:
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The more people know about their eyes, the more they respect the incredible things eyes can do. It’s always our goal to help protect your vision by providing the best diagnosis, treatment, and preventive care.
Top image by Flickr user Sjaak used under Creative Commons Attribution-Sharealike 4.0 license. Image cropped and modified from original.