Why Do Onions Make You Cry
Anyone who has ever cut up onions has asked the question why do onions make you cry? It is a strange phenomenon if you think about it, that the simple act of cutting up an onion brings tears flooding into your eyes. It is not so strange, however, when you get find out the truth about why cut onions make you cry.
So, why do onions make you cry? Simply put, it is the make up of the onion’s cells – and the vapors they release – that cause our eyes to water and burn when we cut into an onion. The offending substance is formally called propanethiol S-oxide, a compound made of sulfur. This volatile substance is released when enzymes in the onion combine with amino acids as the onion is chopped up. When this chemical reaction occurs, the sulfuric vapor is released and floats up to your eyes, causing watering and irritation.
Once the invisible onion gas gets into your eyes, another reaction occurs that makes things even worse. The propanethiol S-oxide reacts with your own tears, forming another compound, sulfuric acid, which causes more burning, irritation and tears – which are actually created to wash away the offending substance.
So, now you’re wondering why do onions make you cry only when they’re raw. Once again, the answer lies in the onion. The inner chemistry of the onion changes when it is cooked, when it is chilled or when it is frozen, so the tear inducing chemical reaction only happens when you are chopping up raw onions that have been kept at room temperature.
Armed with this information, you can see a fairly easy solution to stopping the tears while cutting up an onion: just chill. If you put your onion in the refrigerator or freezer before putting it on the chopping block, there will be no more tears. Cooling the onion slows the chemical reaction caused by the release of enzymes and acids when the onion is sliced into. This limits the vapor released from the onion and eliminates your teary eyes.
Another solution is to cut your onions under running water, although this can be somewhat inconvenient. If you have a cutting board that fits into your sink, it can work quite nicely and you will keep your eyes tear free.
Besides causing eye irritation, the sulfur-based substances found in onions also have a rather strong odor. Again, this is only found in raw onions. The cooked ones definitely have a smell, but it is nowhere near as offensive as that given off before cooking. There are a few tricks that can be used to remove that onion smell from your hands after chopping. Unfortunately, a simple soap and water wash doesn’t always work. What does work is lemon juice. If you rub a little lemon on your fingers, the onion smell should be tamed. If you have a stainless steel sink, here’s another trick for you: rub your oniony fingers along the wet surface of the stainless steel sink and the odor will magically disappear.