A toilet seat scanned this way shows up 220 bright spots. The average mobile phone had 1479.
According to the Daily Mail, Professor Hugh Pennington, emeritus professor of bacteriology at the University of Aberdeen, said: "Swabbing a smartphone is almost like checking your handkerchief for germs - you are likely to find them because of the close physical contact you have with this device several times a day.
"There will be norovirus on phones at this time of year but the bugs on smartphones will probably be people's own bacteria so the likelihood of passing on disease is low. However it might be ill-advised to pass smartphones around between people."
The highest bacteria reading was for a smartphone in a leather case which doubled as a wallet - it showed up almost 17 times the amount of bacteria on a toilet seat.
Experts believe phones become so dirty because they are taken into the bathroom, so are exposed to the same germs as door handles and toilet seats.