If you’ve ever teared up while slicing through an onion or two, it may have left you thinking, “Why do onions make you cry?” It’s a weird process. At one moment you’re cutting onions, and at the next you’re tearing up uncontrollably. If onions make you cry, you probably want answers to this so that you can stop looking like such a wimp and start explaining to people what’s really going on.
At one point in time, scientists were almost positive that the enzyme allinase was the real culprit for the tears streaming down your face shortly after cutting an onion. However, recent studies have proved that lachrymatory-factor synthase (another enzyme inside of onions) is what really induces the waterworks. Literally, when you cut an onion open, this enzyme really wafts up into the air and into your little tear ducts (while creating sulfuric acid in its contents).
However, just as the enzyme makes it into the air, the enzyme practically converts itself into syn-propanethial-S-oxide from unstability. As the syn-propathenial-S-oxide floats up towards your face, your lachrymal glands react to the presence of the chemical and it produces tears.
Overall, onions make you cry due to a basic instability in chemicals. The lachrymatory-factor synthase reacts with the syn-propanethial-S-oxide to cause instability and watering of the tear ducts in the eyes.
The good news is that once you actually cook the onion, the enzymes that cause you to tear up are practically deactivated. This is why you never really see anyone tearing up while eating cooked onions.
If you’re tired of tearing up while cutting through your onions, you can actually turn a fan on and a point in the direction of your work area. This will blow the acidic vapors away so that you can have an uninterrupted session of chopping your onions up!