When your toilet paper is hung underneath the roll, it’s also normally closer to the wall in this position.
Sofia explained: “This increases the risk of coming into contact with bacteria and droplets on the wall surface.
“If you are unfortunate enough to go to the toilet after someone who has covid-19 and the toilet roll is under, not over, you are increasing your chances of coming into contact with the virus.
“There is also a reason why toilet roll bars that have flaps on have the flaps going over, not under”
source: express.co.uk