🧅 Why do onions make you cry?

What you’ll learn

1. The Chemistry Starts With a CutTrace the enzymatic pathway that begins when onion cells rupture and produces a volatile lachrymatory factor.Intact cells keep enzymes and precursors apart. Cutting lets alliinase begin sulfur chemistry and LFS form volatile propanethial S-oxide. The irritant is built after damage, then escapes through the air.
2. The Eye Answers BackExplain how corneal sensory detection triggers protective reflex tearing and distinguish it from emotional crying.The airborne irritant contacts the tear film and activates sensory nerves in the cornea. Reflex pathways increase lacrimal secretion, blinking spreads the fluid, and drainage helps clear the chemical. The wet cheek is protection, not onion-induced sadness.
3. What Changes the TearsConnect cutting, heat, onion variation, and sulfur-pathway branching to differences in irritation and flavor.Exposure varies with cell damage and onion chemistry. Heat disables the fresh enzymatic reaction while other flavor chemistry continues. Tears and flavor share sulfur precursors, but LFS steers only one branch of a larger network.

Questions this course answers

Grounded in trusted sources

• Library of Congress, Why does chopping an onion make you cry? — https://www.loc.gov/everyday-mysteries/food-and-nutrition/item/why-does-chopping-an-onion-make-you-cry/
• Imai et al., An onion enzyme that makes the eyes water (Nature, 2002) — https://www.nature.com/articles/419685a
• Silvaroli et al., Crystal Structure of Lachrymatory Factor Synthase from Allium cepa — https://pubmed.ncbi.nlm.nih.gov/28708375/
• Eady et al., Silencing onion lachrymatory factor synthase changes the sulfur metabolite profile — https://pubmed.ncbi.nlm.nih.gov/18583530/

Every Wunder lesson is built from real, reputable sources — never invented.

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