Why tears while cutting onions

WHY DO WE GET TEARS IF WE CHOP THE ONIONS


It is a very interesting thing that when we cut the onions we will get tears but it doesn’t occurs in case of any other vegetable. The tears you shed when chopping onions aren't emotional ones. We release tears because of sulfur gas.
The sulfur gas is not present in the onions but it formed by the chemical content present in the onions. This gas then gets into our eyes and creates a mild acid which irritates the eyes. Onions consists a chemical known as syn-propanethial-S-oxide. It is an eye irritant which causes our eyes to shed tears when they contact with it. These irritants used to stimulate lachrymal glands ( tear glands ).Recent discoveries says that lachrymatory-factor synthase, is the main factor for our tears.


When syn-propanethial-S-oxide combines with other chemicals in the onion then it forms and releases sulfur gas. It makes us to get tears. For this stimulus the first response shown by us is to close our eyes. Next response shown is tears secretion. At that time we must not rub our eyes as our hands are covered with the acids in the onions.


The scientific explanation behind this process is given as :


When we cut an onion, the cells are ruptured and the intracellular fluid is released out into the air which contain Lachrymatory-factor synthase. This enzyme converts the amino acid found in the onion, sulfoxide into an acid called sulfenic acid. As this sulfenic acid is an unstable compound which will rearrange itself to form a new compound called syn-propanethial-S-oxide. This syn-propanethiol-S-oxide is sprayed into air and if it gets into contact with our eyes. 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 sulfuric acid irritates the nerve endings in the eye, making them to sting.




There are actually two types of tears we usually produce.

Basal type of tears are the tears which are mainly produced for the lubrication of eye surface and these always keeps the eye moist. Whereas the reflexive type of tears are released when our eyes get any contact with the
external stimulant like dust and smoke etc. Such stimulus is taken to the brain by means of nerve endings connects it with cornea. For this stimulus brain releases response to lachrymal glands to produce tears.


Here a new question rises in our mind that “how the onion is getting this sulfur ?”
Onion is a plant belongs to plant kingdom. It belongs to family Liliaceae. The scientific name of the onion is Allium cepa. Along with it, the family contains different plants like garlic, chives , leeks . These plants absorbs the sulfur in the soil when they are given with fertilizers. This sulfur is used in the preparation of a volatile organic amino acid called sulfoxide. These are released out when they are chopped.





REMEDIES FOR THE TEAR BY ONIONS:


The onions are to be kept in cold conditions so that the chemicals may change their natural
character. They also reduce the gas release. If we chew any chewing gums while we are chopping the onions, then we will produce less tears. The reason behind it is explained as : while we are chewing, we respire with our mouth. So the exhaled air blows the gases which tries to reach our eyes. If we use any goggles, then the gases may not reach our eyes. Supplying sufficient amount of water to the onions prevents the release of gases. Eye irritants can, therefore, be avoided by chopping the onions under the running water or by
submerging the onions in the water. Using a sharp blade may not allow the cells to be squeezed off and it minimizes the cell damage and so that less gases are released out.