Onions... oh, why?  

I am hopeless when it comes to onions and I used to make chutney and I used to get my mum to chop the onions and there were a lot and yet she never shed a tear, I couldn't believe it, so I wonder why some cry and some don't.

It's because of the mustard oil in it. I always peel them with googles. It looks very funny.

Have faith in Wikipedia! ;)

"As onions are sliced, cells are broken, allowing enzymes called alliinases to break down sulfides and generate sulfenic acids (amino acid sulfoxides). Sulphenic acids are unstable and decompose into a volatile gas called syn-propanethial-S-oxide. The gas dissipates through the air and eventually reaches the eye, where it reacts with the water to form a dilute solution of sulfuric acid. This acid irritates the nerve endings in the eye, making them sting. Tear glands produce tears to dilute and flush out the irritant.

Supplying ample water to the reaction prevents the gas from reaching the eyes. Eye irritation can, therefore, be avoided by cutting onions under running water or submerged in a basin of water. Rinsing the onion and leaving it wet while chopping may also be effective. Chilling or freezing onions prevents the enzymes from activating, limiting the amount of gas generated. Using a sharp blade to chop onions will limit the cell damage and the release of enzymes that drive the irritation response."

Onions releases sulphur which acts as an irritant to the eye. Eye is sensitive to sulphur and thay makes you cry when you peel onions !!!!

Basically, onions have a protein and an enzyme that when mixed together produce flumes that will react with the tear fluid of the eye and the irritation is weak sulfuric
acid. These two components of the onion are separated by membranes until the onion is cut open. Actually, if you cut the onion under water, the tearing will not happen.

When you cut into an onion it releases sulfur. These molecules mix with your tears and form sulfuric acid. The sulfuric acid burns your eyes and causes them to tear. Problem is that the more you tear the more acid is produced as you continue to cut and it just keeps making you tear.
Fresher onions will cause more tearing than older onions.
Here's a tip: when I buy a bag of onions I will actually sit there and cut them all up at once (some chopped, some sliced) and bag them and toss them in the freezer. That way if I am going to cry I do it all at once. I don't even thaw the onions I just toss them straight into what ever recipe I am using them for.

Any time I take out an onion my poor daughter tells me not to cut it. She doesn't want to see me cry.

i think it is because of some chemicals they emit which serve as a defensive mehcanism. Make sure you wet the onions before slicing them to minimize this tearjerker. I admit, it is irritating sometimes, but it is sometime to live with if you enjoy cooking.

I think it is because of the pungent smell of these onions? Or some chemicals that they emit. I think a botanist could give a clear scientific answer to this.