When an onion is ruptured—such as by a knife—its cells break open and release irritating compounds that form a substance called propanethial sulfoxide, which is similar to sulfuric acid, says Dr. Irwin Goldman, associate professor of horticulture at the University of Wisconsin-Madison.
As the nerve endings of your eyes’ corneas detect the irritant, your brain tells your eyes to produce tears to wash it away. In other words, all that crying is your body’s way of protecting your eyes. (It also seems to help if you block the cornea by wearing goggles—or even contact lenses. Or you could try CHOW contributor Daniel Duane’s method.)
Using “gene silencing” technology, Dr. Colin Eady of Crop & Food Research in New Zealand recently developed a tearless onion by shutting down the gene in the vegetable that produces the irksome substance. It’s still in the development stage, however, and there’s no word yet on whether the new onion tastes better or worse than its weepy relative.
CHOW’s Nagging Question column appears every Friday.
strange, its all about the fumes, i guess the fumes of the onions irritated the eyes as well.... not just the smell of the onions.
I have found that when I have my contact lenses in cutting onions doesn't make me cry but if I don't have them in I will cry. I wonder if anyone else has noticed this.
The irritating compounds in onions are volatile. This means when they are released (by chopping, crushing, blending, etc.) they become airborne - think of fumes. When these fumes reach the eyes, the reaction with the film of tears on your eyes makes a dilute acid which then causes the crying reaction to help rinse out the acid.
Now, the irritating compounds are also water-soluble (if they...+READ
The irritating compounds in onions are volatile. This means when they are released (by chopping, crushing, blending, etc.) they become airborne - think of fumes. When these fumes reach the eyes, the reaction with the film of tears on your eyes makes a dilute acid which then causes the crying reaction to help rinse out the acid.
Now, the irritating compounds are also water-soluble (if they weren't the fumes wouldn't react with the tears on our eyes to produce the acid in the first place), so rinsing knife, cutting board and the onions themselves every so often will eliminate the tears. (It helps if you have quick knife skills too so you can cut everything and get them under water before the fumes get a chance to reach your eyes.-COLLAPSE