Why Do Onions Cause Tears in Your Eyes?

Anyone who has cut, sliced or chopped onions knows that you run the risk of shedding some tears as soon as the knife makes that first cut. But why? What is it about an onion that can make you cry? First of all, the onion, genus Allium, is a bulb plant that grows under the ground. Archaeologists have found evidence that the onion has been eaten since 5000 BC in ancient settlements and in Egypt, Greece and Rome. Ancient people used the onion not only for its taste, but also for medicinal reasons such as cleansing the blood, alleviating headaches, easing coughs and even for reducing hair loss. But it was Christopher Columbus who brought the cultivated bulb onion to the North American continent. (http://en.wikipedia.org/wiki/Onion)

So what exactly is in an onion that makes it react with a human and cause tears? As you might have guessed, it's a chemical. The chemical is a sulphenic acid which will change into a gas that spreads out in the air. When the onion is growing in the soil, it picks up sulfur that's in the soil. http://www.loc.gov/rr/scitech/mysteries/onion.html) This sulfur is what makes the sulfoxides that end up as sulphenic acid. Anyone susceptible to this chemical, and within the area of the gas, will feel stinging and tearing as the gas reacts with neurons of the eye. The eye instantly wants to wash out the foreign gas, so it creates tears to flush out the offending gas. The gas is released when the skin of the onion is cut, causing the enzymes to be exposed. (recipes.howstuffworks.com/question539.htm)

There are several ways to ease or even prevent altogether the reaction of the sulphenic acid that makes the gas. The easiest is to run water over the onion or keep the onion in a bowl of water while cutting. The gas can't escape the water and will therefore not become airborne. Another way to reduce the enzyme gas reaction is to leave the root end of the onion intact. A lot of enzymes are stored in the root, so by not cutting into the root, those enzymes won't be released. Also, if you cut through an onion with a very sharp knife, fewer enzymes will be released because the skin cells of the onion won't be as damaged. You can also try freezing an onion and slicing it when frozen, preventing the reaction of the acid.

A few other ways to reduce the incidence of getting the gas into your eyes is by wearing snug fitting swimming or ski goggles. Using an onion chopper or food processor will also help to keep the gas contained while chopping. It may take a little trial and error to find an effective method for protecting your eyes, but it'll make dealing with onions far easier, and let you still enjoy this tasty bulb. (http://www.astray.com/recipes/?show=No%20more%20tears%20about%20onions)