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Home / Newton Desk / Why Do Onions Make You Cry and How To Prevent It?

Why Do Onions Make You Cry and How To Prevent It?

Have you ever notice that when you chop an onion, you begin crying, and touching your eyes only can makes it worse. But why does it happen? what’s the scientific theory behind this? Let’s get the answer of why do onions make you cry?

About Onion

Onions contains nonmetallic chemical element which is sulfur amino acids sulfoxides. which affects our eyes. When we cut an onion, their cell walls get rupture (break). And the chemical which is found in onion cells is the lachrymatory factor synthase enzyme. This enzyme is volatile, that is, it easily evaporates at normal temperature. This acid gets mixed with enzymes and forms a gas known as propanethial-S-oxide (C­­­­­­­3H6OS), That chemical is syn-propanethial-s-oxide.

onions cry chemical syn propanethial s oxide

When this gas reaches your eyes and it reacts with the substance which is basal tears, that keeps our eyes lubricated, and forms mild sulfenic acid (RSOH). Can you believe that you’ve acid in your eyes? Absolutely yes, this sulfenic acid produced burning sensation in our eyes.

sulfenic acid RSOH

To understand the whole phenomenon of this, we need to know about the anatomy of the eye. what’s the anatomy of Human Eye?

Anatomy of Human Eye

As we can see here, lens is present in our eyes. This is a convex lens and changes its focal length with the help of these ciliary muscles. This middle dark muscular structure on the outside is called iris. We have a pupil, which is circular in structure, it controls how much light should reach our eyes. Cornea covers the iris, And this cornea is present at the anterior part of our eyes. It is transparent membrane.

anatomy of human eye

Types Of Tears

Do you know the tears that comes out from our eyes are of three types which are following:

1) Emotional tears; when we feel so happy or sad then that tears comes from our eyes is called emotional tears.

2) Reflex tears; these tears are result of when foreign particle enters in our eyes, that can damage or irritate our eyes, then these tears come to wash out that thing are called reflex tears. amount of these tears is larger than basal tears.

3) Basal tears; the tears that release continuously in small quantities to lubricate the cornea and moist the eyes, which can protect our eyes from dust particles and harmful objects. When this chemical called syn-propanethial-s-oxide comes in contact with basal tears or cornea, with the help of these ciliary nerves, our brain can identify that there are some problems. And this chemical is the root cause of all problems. immediately our brain gives signals to lachrymal glands to release tears to remove chemical from our eyes. This lacrimal gland will release tears, and this syn-propanethial-s-oxide chemical will be washed out.

lacrimal gland and onion cry tears

How Can we Prevent Onions Cry?

There are some facts which can reduce tearing while chopping onions;

1) You can freeze onions. When you keep onions in freeze, their temperature will be low. So it will be easier to cut them. And can prevent us from crying. cause it will minimize the amount of gas released into the air.

2) You can wear glass tight goggles while chopping onions.

3)  You can use sharp knife to cut onions.  it can cause less rupture of cell walls.so, onions will be releases less enzymes into the air.

4) You can keep onions in cold water.

5) Chewing a bread helps us to shedding tears from our eyes. Cause bread can absorb the sulfuric compounds before they can reach our eyes.

6) If you microwaving onions for some time before cutting. It can helps you in reducing tears from your eyes.

7) You can use spoon while chopping onion. You can pop a spoon into your mouth before you begin cutting an onion.

8) You should cut the onion under water. Cause under running water sulfuric acid cannot reach to our eyes. And it won’t make you cry.

9) You can cut the onion near to an open flame cause sulfuric compounds reacts with flame.so it can prevent us from crying.

10) You can cut the root intact. It may help you while chopping an onion. It can protect you from shedding tears.

Onions Cry Chemical Reaction Mechanism

So, if we would say one line what’s the main reason of crying when we cut an onion, then answer is chemicals. Onion contains these chemicals. That’s why it make us cry while chopping an Onions. The main root cause of this problem is syn propanethial-s-oxide chemical. Because of this chemical our eyes shedding tears. But we can cut an onion without crying. We already mention these techniques and facts which prevent us from crying. Here one question is arising; why do some onions have more of an eye stinging effect than others?

Generally, the plants often try to defend itself by releasing bitter taste chemicals called polyphenols that can be distasteful to hungry animals trying to eat it. but an onion for their defense mechanism producing a more irritating chemical, syn propanethial s-oxide. This chemical in starting known to be one enzyme which is Alliinace (C6H11NO3S), but onion has absorbed Sulphur from the soil and converted into eye irritating chemical called PRENSCO (1-propenyl-cysteine sulfoxides) but when the onions is ruptured (break), it release the alliinace, which reacts with PRENSCO to produce ammonia and other chemical called 1-propenyl sulphenic acid.

alliinase iso alliin onion reaction chemical

The second enzyme known as lachrymatory factor synthase (sulphenic acid). Then it turns into the chemical called propanethial s-oxide. this chemical is the main reason of the irritation in eyes as we earlier studied that but some onions have more than others. Actually, it depends on the amount of the Sulphur compounds which onion has absorbed from the ground it can depend on the condition of the soil.

If soil has much amount of Sulphur, it will help in growing or yielding of onions. Sweeter onions release less amount of Sulphur compounds. Now you are thinking about garlic, Why garlic does not produce eye stinging liquid? cause garlic contain different compound called prensco2 or alliin, which doesn’t breakdown into eye sting chemicals. instead, it produces allicin, which has many health benefits. Hope, now have get the knowledge of whole process of why Onions make you cry… 

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