why do onions make you cry

Why Do Onions Make You Cry?

Have you ever wondered why chopping onions can bring tears to your eyes? Let’s dive into the onion biochemistry to uncover the truth behind this common kitchen phenomenon.

Q. Why do onions make you cry?

A. Cutting onions can trigger tears due to the release of a compound called syn-Propanethial S-oxide, also known as (Z)-propanethial S-oxide. This compound is a lachrymatory agent, meaning it induces tearing and stinging sensations upon contact with the eyes. When onions are sliced, their cells are ruptured, releasing enzymes known as alliinases. These enzymes break down sulfur-rich amino acid sulfoxides present in the onion, leading to the formation of sulfenic acids. Specifically, 1-propenesulfenic acid is rapidly transformed by an enzyme called lachrymatory factor synthase (LFS) into syn-Propanethial S-oxide. This volatile compound diffuses through the air and upon reaching the eyes, stimulates sensory neurons, causing irritation and prompting the tear glands to produce tears in an attempt to flush out the irritant.

Q. What causes the burning sensation when chopping onions?

A. The burning sensation experienced when chopping onions is caused by the volatile nature of syn-Propanethial S-oxide. This chemical easily vaporizes and floats up from the cutting board, coming into contact with the sensitive tissues of the eyes. Once it reaches the eyes, it triggers a stinging sensation, prompting the brain to initiate a tear response to wash away the irritant.

Q. Are there similar compounds found in other plants?

A. Yes, a structurally related lachrymatory compound called syn-butanethial S-oxide has been discovered in another genus of plants, specifically Allium siculum. This suggests that the ability to produce lachrymatory compounds may be a common trait among certain plants in the Allium genus.

Q. How can you prevent tearing while chopping onions?

A. There are several methods you can try to minimize tearing while chopping onions:

  • Use a sharp knife to minimize cell damage and reduce the release of irritant compounds.
  • Chill the onion in the refrigerator before cutting to slow down the release of lachrymatory agents.
  • Soak the onion in water before chopping to help dissolve the sulfur-rich compounds.
  • Wear protective eyewear, such as swimming goggles or ski goggles, to shield your eyes from the irritants.
  • Use a ventilator or fan to blow the volatile compounds away from your face while chopping.

By understanding the biochemistry behind onion-induced tears and employing these prevention methods, you can make chopping onions a tear-free experience in your kitchen.

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