Why do onions make you cry?

22nd July 2009
Why do onions make you cry?

Asked by: Sara Green, Leicester

The action of cutting an onion releases a fine spray of droplets. Recent Japanese research has shown that these droplets contain an enzyme called lachrymatory-factor synthase and sulphur-containing compounds, which react to produce a powerful irritant called Syn-propanethial-S-oxide. When a droplet strikes your eye, you respond by producing a copious flow of tears to try and wash the irritant away.

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