May I ask why you're using them at all? Every time I look at Japanese cities they seem to have PM2.5 levels in a second-digit microgram range. A bad day seems to be something like 15 µg.
First off I don't want to under sell Japan, it is a pretty nice country and Tokyo is pretty clean. Sadly it's still a city with car pollution all cities have.
Unique to Japan is the pollen. After WW2 Japan was reforested in mass with a single variety of tree. Thus making the exact pollen release an annual torture test for anyone without air filters. My theory is everyone eventually gets pollen alergies, it's just a matter of time. My wife is affected during pollen season, and I've starting to notice myself become affected as well.
We do not stir fry, that's not a thing in Japanese cuisine. And our cooking is all IH so no gas particle. Yet even we will notice if the air purifiers are not running. We'll first notice our noises are a bit stuffy, and omly then check to find a kid has turned off the air purifier.
Candles, cleaning, frying. All very good ways to increase air pollution in your home that nobody speaks about.