Edit: Swim goggles should work too if you don’t have to worry about glasses.
I know this will be obvious to some, but I’ve never seen anyone in my family wear them. It’s so obvious once you think about it, and yet I’d wager most people (especially ones who don’t cook as a hobby) have never tried this.
The reason you cry is because slicing onions produces an organosulfur called syn-Propanethial-S-oxide. Lab goggles – as designed – keep the chemical irritant from reaching your eyes. I’ve used them hundreds of times now, and I think there was one time it got into my eyes when I didn’t have the goggles situated right (not difficult; I was just being a moron).
My 3M anti-fog pair were about $5 USD when I got them, and it looks like they’re about $7.50 USD now. For that price, I never have to dread cutting up onions again. It’s not magic; it’s just basic PPE, and it works. You can even wear them over eyeglasses (I’m sure some huge, circular frames won’t fit, but most should).
Even if you forget them and remember them midway through slicing, it can still help somewhat. So even if you’re as absent-minded as I am, you can benefit from trying this.
These (below) were the ones I got personally, but feel free to try what you already have if you already have a pair on-hand for e.g. cleaning. I’d assume the important thing is just that they’re goggles, not glasses.
Why YSK: owie, oof, ouchie, my eyes. Cooking is just DIY organic chemistry.
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.
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.)
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.)