More than one in 10 people's hands are so contaminated with faecal organisms that the levels of bacteria detected were equal to what you would expect to find in a dirty toilet bowl, a study suggested.
Out of the samples taken, 11% of hands, 8% of bank cards and 6% of bank notes showed this form of gross contamination.
In Britain, one in 10 bank cards and one in seven notes were found to be contaminated with some faecal organisms and more than a quarter of hands sampled showed traces of faecal contamination including bacteria such as E.coli.
The 272 participants who took part in the scientific study for Global Handwashing Day were also asked to fill out a questionnaire with the results revealing only 39% of respondents washed their hands before eating.
The vast majority (91%) of respondents also stated that they washed their hands after using the toilet, although the levels of faecal organisms contaminating the cards and currency suggested otherwise, researchers said.
Washing hands with soap can reduce diarrhoeal infections by up to 42% but only 69% of people reported doing this whenever possible.
How to wash your hands properly
Dr Val Curtis, from London School of Hygiene & Tropical Medicine, said: "Our research shows just how important handwashing is - the surprising levels of contamination that we found on everyday objects is a sign that people are forgetting to wash their hands after the toilet, one of the key moments for infection prevention."
Samples were taken from 272 people from east and west London, Birmingham and Liverpool - and in total 816 specimens were collected.
Of the samples taken, the cards and notes in Birmingham showed the most contamination, with faecal matter detected on 17% of specimens. More than one in three hands sampled from Birmingham harboured traces of faecal contamination.
A fifth of hands surveyed in east and west London were found to have traces of faecal contamination. The most "grossly" contaminated cards and notes came from east London with 8% of cards and 11% of notes holding levels of bacteria that were comparable to a dirty toilet bowl.
Dr Ron Cutler, who led the research at Queen Mary, University of London, said in a statement: "Our analysis revealed that by handling cards and money each day we are coming into contact with some potential pathogens revealing faecal contamination including E. coli and Staphylococci.
"People may tell us they wash their hands but the research shows us different, and highlights just how easily transferable these pathogens are, surviving on our money and cards."
Nick Wilcher, marketing manager of Radox, who funded the study to raise awareness of Global Handwashing Day, said: "Our research highlights just how much bacteria we are exposed to in our everyday lives, on objects such as money and cards. We hope this study makes people think twice and encourages people to wash their hands after going to the toilet and before eating."