What is it that irritates your eyes and makes you cry when you peel onions?

The synthase enzyme converts the amino acids sulfoxides of the onion into sulfenic acid, not Sulfuric acid!

Should be sulfenic

More of the sites on the Internet quote Sulfenic Acid (RSOH) as the chemical that makes you cry. Your quoted site and your explanation cite Sulfuric Acid (H2SO4). Sulfuric acid would normally be identified by a rotten egg smell which is absent in cutting onions. While I would assume that Sulfenic and Sulfuric acids are closely related, I think this dichotomy needs to be clarified.

Stevie G, Sulfenic ... not Sulfuric.

Someone said to peel onions under water but I couldn’t hold my breath long enough to finish one.

The correct answer is sulfenic acid - not one of the choices!

Bull. It is not SULPHURIC ACID.

It's Sulfenic acid, not Sulfuric. Damn, that's two in a row.

This is an incorrect answer. How did it make it through review. The acid is sulfenic not sulfuric. If it was sulfuric you would burn your hands.

Martin Retzolk, which combines with water in the eyes to form a mild sulfuric acid?

Knew it was the fumes, but not what type. But I know those fumes are NOT sulfuric acid!

Even the kookaburra sang SULFENIC up in the old gum tree!

Pas l'acide sulfurique !!!....

Yes, wrong answer, it is sulfenic acid

Bill Coe, sulfuric acid is odorless, it does not smell like rotten eggs. The sulfur compounds in eggs smell like the characteristic ‘rotten egg’ odor.

Wrong, so wrong. The chemical is syn-Propanethial-S-oxide, aka sulFENIC acid, NOT sulfuric acid. Ruptured onion cells release special enzymes as well as amino acid sulfoxides which combine to form sulfenic acid. If onions leaked sulfuric acid, we’d all be severely injured, no one could eat them. How did this question get through?

There is no correct answer presented. The onion produces SULFENIC acid, not sulfuric acid. Does anyone actually check these answers?

Wrong answer--AGAIN!

The culprit is called the lachrymatory factor, a chemical that irritates the eyes. When the onion is intact, a group of compounds called cysteine sulfoxides are kept separate from an enzyme called alliinase. But when you slice, dice or crush the onion, the barrier separating the compounds and enzyme is broken. The two come together, setting off a reaction: The alliinase causes the cysteine sulfoxides to become sulfenic acid. i want my point because answer is wrong

OOPS! I accidentally entered my comment before completing it. Sulfenic acid is present in onion. Sulfenic acids (amino acid sulphoxides) are unstable and decompose into a volatile gas. The gas dissipates through the air and eventually reaches the eye, where it reacts with the water to form a dilute solution of sulphuric acid. In chemistry, sulfenic acid is an organosulfur compound and oxoacid with the general formula R−S−OH. It is the first member of the family of organosulfur oxoacids, which also include sulfinic acids ( R−S(=O) 2H) and sulfonic acids ( R−S(=O) 2OH), respectively.

Your correct answer is only partly correct, Brian. I had heard about sulfuric acid but realised there was more to it. Here is some more info for you.

Another Frank Cowell question where you have to guess which wrong answer he has marked as correct. Its sulfenic acid not sulfuric. Sulfuric acid is a corrosive substance which is destructive to the skin, eyes,teeth and lungs.This is from the Centers for Disease Control and Prevention( THE CDC) and an American government agency.Get with the Program Frank and quit the trick questions or listing an incorrect answer as correct.

I think this needs a correction - just saying I agree with all the others who've noted that sulfenic and sulfuric are not the same thing...

I found the explanation informative and interesting.