See What Makes Us Cry When Peeling/Cutting Onions

Have you ever wondered why you cry and and feel this stinging sensation when you peel or cut onions? Or you just simply don’t care enough to know? As a student of Food Science and Technology, I did a little digging about it around 2008 and knew the reason why we cry when we peel onions. The chemistry is just very simple and I am going to make this article as short as possible. The stings and pains in the eye are caused by something in the onion but the crying is caused by our brain. You can’t blame the brain, it’s only trying to help reduce the pain.

So, What Causes Your Eyes Release Tears In Onion?

Peeling, cutting, dicing or crushing an onion means you are cutting the tissues. While doing this, several components in various cells mix together to produce the substance that causes the painful stings in the eye. That explains in to the layman.

If we want to go a little bit technical, during the growth of onions on the field, it absorbs sulphur from the soil. When we cultivate and peel or cut this onion, it breaks the cells within the onion like I explained above. This action releases certain enzymes in the Onion. The enzymes react with the sulphur, creating amino acid sulphoxides.

When this happens, it creates the highly unstable syn-propanethial-S-oxide, which is a combination of sulphuric acid, sulphur dioxide, and hydrogen sulphide. Syn-propanethial-S-oxide in its gaseous state is able to diffuse out into and around the room where you are. It then comes in contact with the water in your eye, which triggers a burning/stinging sensation via the ciliary nerve of the eye.

How Our Eyes and Brain Reacts To This

Lachrymal gland, found just above the eyelids is responsible for regulating tears in the the eyes. When the irritation start and you feel the stings in your eye, the brain gets  the message and decides to react to help relieve the pain. The brain pushes the lachrymal glands into releasing the tears, trying to flush the irritant out of your eye(s) with the tears. This does not happen in onions that we have cooked because cooking heat already inactivates the enzyme needed to make the troublesome syn-propanethial-S-oxide.

So, now you know what causes the burning sensation in your eye when you peel onion and why you cry shortly afterwards.

COMING TOMORROW: 3 Tricks That I Use To Cut/Dice Onion Without Crying [Works]

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