Why onions make you cry

Dramatic cinematic portrait movie poster, 1024x1536, with the title 'How Onions Trigger Tears' in LARGE, BOLD, fully legible text in the top quarter, and the only text in the image. Below the title, show a close-up of a cut onion releasing a glowing chemical mist toward a watery human eye, intense lighting, scientific documentary style, high contrast, realistic.

When onion cells are cut, alliinase and lachrymatory-factor synthase help create syn-propanethial S-oxide, the volatile lachrymatory factor that escapes into the air.

Portrait orientation, realistic science-documentary image of a sliced onion with invisible enzymes conceptually shown as glowing chemistry around the cut layers, releasing a faint vapor cloud into the air.

That vapor dissolves in the tear film, forms a mild acid, and irritates corneal sensory nerve endings described as trigeminal pain receptors or nociceptors.

Portrait orientation, close-up scientific illustration of onion vapor reaching an eye, dissolving into the tear film, with corneal nerve endings highlighted in a realistic medical style.

The trigeminal signal then tells the brain to drive the lacrimal glands, flooding the eye with tears to dilute and wash away the irritant, and the effect is usually weaker with low-sulfur onions, freshness, a sharp knife, chilling, good airflow, the root end saved for last, and snug goggles rather than ordinary glasses.

Portrait orientation, cinematic kitchen scene showing an onion being cut with a sharp knife near a fan and goggles, with a subtle tear-response concept and cool refrigerated onions nearby, realistic and dramatic.

How Onions Trigger Tears

When onion cells are cut, alliinase and lachrymatory-factor synthase help create syn-propanethial S-oxide, the volatile lachrymatory factor that escapes into the air.
That vapor dissolves in the tear film, forms a mild acid, and irritates corneal sensory nerve endings described as trigeminal pain receptors or nociceptors.
The trigeminal signal then tells the brain to drive the lacrimal glands, flooding the eye with tears to dilute and wash away the irritant, and the effect is usually weaker with low-sulfur onions, freshness, a sharp knife, chilling, good airflow, the root end saved for last, and snug goggles rather than ordinary glasses.

Why do onions make you cry?

Volatile Sulfur Compounds in Food

Propanethial-S-oxide

syn-Propanethial-S-oxide - Wikipedia

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_syn_ -Propanethial-_S_ -oxide — Grokipedia

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Why onions make you cry

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