I am inclined to agree. The irritant is not an acid but a complex sulphur compound generated by physical damage to the onion, it is part of the natural defences of the onion family against predators eating them.
The irritant is water soluble but I see no reason for it to be absorbed by nearby wet paper enough to matter. I think this is one of those “weird tricks” or “genius hacks” that may happen to some degree but not enough to be important.
Two other suggestions are:
chilling your onion, this will reduce the speed of the reaction that creates the irritant as well as the vapour pressure of the irritant and so the amount in the air is less, my guess is this would be the best method,
using a sharp knife, this will lessen the damage to the onion and hence the amount of irritant generated.
How well these two work in practice would require testing, so they may be in the same category of methods that ought to work but don’t really matter.
A method that will work for sure is cutting your onion under water but it is hardly convenient and in my view a way to increase the risk of cutting yourself.
I really doubt the “Hack” works, but I’ll give it a go. I doubt the “science” that the acid that makes your eyes water is attracted to a running cold tap or a wet paper towel on the other side of the chopping board.
When I was in Boarding School, the fees were kept down by getting students to work in various areas such as chopping vegetables. We tried “everything” with onions. A slice of toast or bread hanging out the mouth, cutting under water, under a cloth, after soaking them, wearing sunglasses, peg on the nose (to breath through the mouth thus stopping the fumes going up towards the eyes), various herbal concoctions, garlic placed nearby. There was running water near as others washed potatoes, filled pots, washed up, and lots of wet tea towels but that didn’t work. We never found a solution. I doubt this “hack” has either.
We did solve the problem of cutting up Qld Blue pumpkins - we dropped them off the balcony on to the concrete steps - until the cook found out!
