Does placing a wet towel nearby when slicing onions prevent crying?
The reason slicing onions makes cooks cry is a complicated reaction between various enzymes released from the onion's sliced cells that produce an irritant, propanethial S-oxide.
When this comes in contact with the human eye, crying is the result -- the body's response to try to flush the irritant away. There is no evidence that free-floating propanethial S-oxide in the air is drawn to water or that a moist towel nearby would reduce the amount of irritant that could potentially come in contact with eyes.
Lead Stories found no evidence that indicated onion enzymes are drawn to water or moist surfaces. Water is already present in the onion.
There are some onion-chopping anti-crying tips that do include water -- cutting onions under water or under running water, but in these cases the water becomes a barrier to the eye irritant.