gottem

this meme is wrong

what really happens is that this thiopropenal S-oxide attacks free thiol in one receptor that usually detects spicy smells, much like about any modern tear gas (CN, CS, CR. also allyl isothiocyanate from mustard and many, many, many other alkylating things). there's no acid involved

I don't know whether to believe the meme or the comment on the meme.
Onions spew enzymes and sulfenic acid when their skin is broken. These compounds combine to produce propanethial S-oxide, an irritating gas.

Propanethial S-oxide is a lachrymatory agent, meaning that it generates tears when it touches the eye. Propanethial S-oxide turns into sulfuric acid when it touches the water layer that covers and protects your eyeballs.

Source

I'm not a chemistry guy though.

I am especially sensitive to this. I’ve found that using a very, very sharp knife can help, but some onions are especially strong. At that point I’m breaking out the swimming goggles.

I thought I was the only one who cuts onion with goggles. If I only need one onion I don't need them if I am quick enough, but if I need more than that, I always whip out swimming goggles.
Run your wrists, palm up, under cold water. It's black magic. It will stop it almost instantly.
- I am going to try this, but I’d really like to know why it works. Someone else suggested cold water on the knife. Do the irritant molecules from the onion react with the water on your hands/wrists/knife before getting up in your eyes?
Try slicing a lime or lemon before cutting onions.

It's hard, but don't blink. If you blink it gets under your eyelids. If you don't, the tears just continuously wash it down.

Apparently doing this will literally help

I think that just generally helps with life
I don’t get it, bite into something, or eat something sweet?
- Holding bread in your mouth.

I just got a knife sharpener and it actually helps.

After sharpening, my eyes couldn’t even tell that I was cutting an onion.

Instructions unclear, now I have pointy eyes
- Instructions unclear, I can't see anymore
my eyes couldn’t even tell that I was cutting an onion.

Because you have sharpened and blinded yourself......
this works because the pain is caused by an irritating gas released when you crush the onion cells and some compounds mix together and react, with a sharp knife fewer cells are crushed so there's less gas

At some point I started running cold water on the knife before cutting and onion, and it seems to help. Does anyone know if there’s science behind this, or am I making shit up?

Others in this thread have pointed out that running cold water over your arms helps. So maybe while you wet your blade, your arms get wet too...?
Maybe it lubricates the knife so that it crushes fewer onion cells. That is the reason a sharper knife also works. Or the water dissolves part of the escaping gas. I think it might be both.