Cutting onions makes your eyes water because they contain a highly irritating substance called n-propanethiol.

When an onion is peeled or cut, the n-propyl mercaptan in it volatilizes into the air. If it "slips" into people's eyes, it will feel very spicy, and the reaction of the eyes will be tears.

The method you mentioned, "use tissue paper to block the irritating gases from entering the nasal cavity, and some say wear diving glasses" is to prevent volatile gases from entering our eyes.

That's the truth.

In fact, we can also take advantage of the fact that n-propyl mercaptan is soluble in water. Every time when cutting onions, we can put some water in the basin, and then put the cutting board in the water to cut the onions, so that n-propyl mercaptan is partially soluble in the water.

It can reduce the irritation to human eyes.