When I was little, my mother was always cooking. Because there are six people in my family, she would spend hours in the kitchen making us large and delicious dinners. Being around this sparked my interest in cooking, and I always loved to help out. I typically get preparation tasks like chopping tomatoes or garlic, or onions. My mother was always quick to give me the job of chopping the onions, because she, along with almost everyone ever, hates when your eyes start to tear up. I’ve always been very curious as to why this happens.
It turns out, that when we cut into onions, there are chemicals being released. Inside of onions, there are both enzymes and acids that are found in different sections of the onions. But when we slice our knife into them, we end up mixing these substances. When combined, they form propanethiol S-oxide, which is a gas that will then go to our eyes (Science Bob). Here is a quick video that helps to further explain this process. And here is a very scientific explanation of what happens.
Once these gases escape the onion and go to our eyes, they begin to tear up. What next? Most people will want to rub there eyes, which you shouldn’t do because you have those chemicals on your hands from touching the onion. Blinking and closing your eyes when they get irritated will help to flush out the irritant. But what can we do to prevent this sensation from happening at all?
There are many claims about ways to prevent your eyes from tearing up when chopping an onion. Some interesting ones include holding bread in your mouth, holding matches in your mouth, burning a candle near by, and using a cold knife to chop the onion. Unfortunately, these tactics have been proven false. But there are a few tricks that have been proven to help lessen or sometimes even prevent the tears. The next time you need to chop an onio
n, try putting it in the fridge a few hours before you need to cut it up; this will help to chill the enzymes and slow down the reaction when it is cut into. Another trick it to wear goggle, which I know sounds crazy. But by wearing goggles, your eyes are protected and the gas is unable to get into your eyes.
So the next time you find yourself chopping onions, I hope that you’ll finally understand why you are crying, other than the fact that your mom is making you help cook dinner.
My eyes water like crazy when I cut onions and I heard of the trick of opening up the freezer to stop them from watering. I think this is similar to putting the onion in the fridge before cutting it so it chills the enzymes. I don’t know if the freezer trick is scientifically proven to be effective but I think it has worked for me. I’ve never heard of the other tricks to get it to stop that were proved wrong but they made your post interesting to read!
Like your mom, I can not stand cutting onions. In fact, I leave the room when onions are being cut. It was very interesting to see your research results about why our eyes tear up since I have heard many theories. It makes sense that chemicals are released from the onions, but I did not know that it was a result of enzymes and acids mixing together. It’s strange to think that you are setting off a chemical reaction just by cutting an onion. Also, the solutions you provided, well, I guess I can’t make fun of my cousin quite as much when he pulls out swim goggles to help when he’s cutting onions. Also, it’s very helpful to know that those other theories don’t work, so now I won’t try them. Finally, the picture in your post made me curious about whether animals’ eyes are affected by onions as well. There isn’t much information on the topic, but I found that ingesting onions, at least, is extremely dangerous for cats and dogs. It would be an interesting topic to look into for pet owners.
Hi Madeline, I found your post interesting because I just finished up a post about why we cry, and I found out that we cry certain reflex tears when onions irritate our eyes. It was very interesting to find out more about why the onions irritate our eyes in the first place!