You don't, it actually works really well unless the onion has already started breaking down and is "juicy."

If you want to use as much of the onion as possible, just slice across normal until you get down to the small core section near the root. Then rotate and make a couple slices to separate the core then chop the slices.

The onion around the core tends to be the tougher bits so tossing it isn't a generaly a big deal but that's how you recover all the good parts.

Just put water in your mouth and hold it in, works fine.

Some of the suggestions in the replies are kind of baffling to me in the face of an effectively foolproof, dirt-cheap, comfortable, and trivial solution with basically no downsides. Like you do you, but "yeah, just hold water in your mouth for the indeterminate amount of time you spend cutting up onions" is so ridiculous compared to just saying "here, try some basic PPE".

It's hard to imagine even doing that routinely without thinking "surely there's a better way??" and stumbling upon this.

No need for a sharp knife, just don't breathe with you nose (or don't breathe at all while cutting).

I honestly thought it was just me. No reaction at all, dull knife white onions nothing

in the face of an effectively foolproof, dirt-cheap, comfortable, and trivial solution with basically no downsides

you mean sharpening your knife, opening a window or turning on the vent fan?

Yeah, I cut the root to a nub, just enough to essentially clean the bottom, but not enough for the onion to fall apart. But same as you: whatever I don't finish lasts over a week, and I chop up everything that remains and use all of it.

you mean sharpening your knife

Helps, and you should be doing it anyway; not 100% effective, as I always keep my knife sharp. I could cut more slowly too (empirically shown to help), but why would I? I'm not at all recommending against knife-sharpening, because regardless of onions, a dull knife is a safety hazard.

opening a window

I've never lived in a house where the window is less than 5 meters from any kitchen countertop. Also heavily dependent on the weather (pollen count, haze, storm, obnoxiously high wind or too calm to help, way too cold or way too hot, etc.)

or turning on the vent fan?

Yeah, I'll just move my cutting board underneath my stove's vent fan like a low-rent fume hood instead of just slapping on some unobtrusive goggles from the drawer. You can, but this is a bootleg solution I'd use at a friend's house, not when I cut up onions once a week.

The fact that you listed "opening a window" as "comfortable" (*gestures broadly at the weather*), "dirt-cheap" (*gestures broadly at heating and cooling costs*), and "trivial" (not if you don't have one; look at typical apartment layouts if you think this is uncommon) is what I'm getting at: people have suboptimal, often nongeneralizable half-solutions to this easily solved problem and then try to "or you could just" when someone suggests basic PPE.

I'm not baffled people have solutions that work well enough for them; I am baffled at suggesting them over the clearly optimal solution for the most general audience. (Disclaiming as "general audience" because contacts seem to have it beat when you already wear them; couldn't say for sure.)

Cut vertically (with the veins). You basically get no stinging that way (until you start cutting horizontally)

Cold buddha shivers, hot buddha sweats, onion-chopping buddha cries 🧘‍♀️

Or a small fan to blow/suck it away from you

That makes sense, and is what I do. I would call this "cut off the root last" instead of "don't cut off the root."

For me the biggest factor is the age of the onion, which can be quite aged before it reaches you the consumer, especially with recovered produce.

I just cut the onions on the stove with the ventilator running. It allows me to slice/dice/mince the onions however which way I want without any tears.

yep. I just blow it into the living or dining room. easier for half a dozen people to deal with it than just myself

as a kid I developed a resistance working in a kitchen

as an adult it somewhat continued due to onions being an important part of every meal

but sometimes you just get one of those fuckers that's so goddamn juicy that the mere sight of it brings you to tears

every great once in a while, I get a bit of a twinge and a tear, but it's very rare

Literally never had that happen. And it's often more than half a dozen people in the room the fan faces. Concentration of it is too diluted by the air from the fan or something. Not sure why it doesn't have the effect but I've never had a problem in that regard.

Seems like it might make sense but is not my experience, anecdotal evidence being what it is

We didn't install an eye wash station for you to use goggles.

same. and usually at somebody else's house, too. even if I bring my own (sharp) knife lmao

are we still talking about onions ;)

"Onions make me sad, a lot of people don't realize that. When I'm cutting onions, I'm sad. Because the plight of onions, it's sad. But people don't realize I'm actually crying - they think I'm just reacting."

Mitch Hedberg

Everyone should own some eye protection. A quality respirator is also extremely useful and very wise to have around in many circumstances.

The vapour released is attached to the moisture in your eyes so just stick your tongue out for the duration of the onion cutting and you'll be reet

Let's pull out the breathing mask one uses for spray paint and invite someone over for dinner /s and /j

It's a bit like overdoing wasabi, I don't really do it deliberately and don't particularly enjoy it in the moment, but it makes me feel very alive!

If you cut onions with a knife, sure. I use a Japanese mandolin called Benriner that is so sharp that I can get through several yellow onions before I start having issues.

And I'm confirming 😉