This seems like something that should be true, but I think I remember seeing a Mythbusters episode where they decided it didn’t make a difference. That show was more about entertainment than science, so I wondered if there was a more rigorous study done? I’ve definitely seen splashes of water(?) come out from flushes so that alone seems to argue for closing lids.
I remember watching a video where they added some liquid visible with UV to the water and flushed, there were droplets everywhere including the tester’s face.
It’s not a study but it’s enough to make me close the lid, especially when my toothbrush is in the same room.
The real question is wether it has an effect which matters. Does it impact your health? Does something get damaged by becoming wet? Things like that.
I’m pretty sure there is next to no such effect. Which still does not mean this is the answer!
I think the actual answer is to do what feels better for you. This has probably a much bigger effect on your health than actual droplets.
