Just one in 20 people wash their hands for long enough to kill harmful germs after visiting the toilet, a new study has revealed.
Furthermore, a third do not use soap and 10 per cent do not wash their hands at all.
The research named and shamed men as particularly bad at washing their hands correctly.
The study by environmental health experts at Michigan State University in the U.S., was based on observations of 3,749 people using public toilets.
Lead author Professor Carl Borchgrevink, associate professor of hospitality business, said: "These findings were surprising to us because past research suggested that proper hand washing is occurring at a much higher rate."
Hand washing is the single most effective thing to do to reduce the spread of infectious diseases, according to the U.S. Centres for Disease Control and Prevention.
Failing to sufficiently wash hands contributes to nearly 50 per cent of all food borne illness outbreaks, it said.
Experts say it takes 15 to 20 seconds of vigorous hand washing with soap and water to effectively kill the germs which cause infections.
Yet the study found that people washed their hands for, on average, only about six seconds.
Professor Borchgrevink's team observed hand washing in toilets in bars, restaurants and other public establishments.
The study claims to be one of the first to take into account factors such as duration of the hand washing and whether people used soap.
Among the findings were that 15 per cent of men did not wash their hands at all, compared with seven per cent of women and when they did wash their hands, only 50 per cent of men used soap, compared with 78 per cent of women.
People were less likely to wash their hands if the sink was dirty and hand washing was more prevalent earlier in the day.
Professor Borchgrevink said this suggests people who were out at night for a meal or drinks were in a relaxed mode and hand washing became less important.
People were also more likely to wash their hands if a sign encouraging them to do so was present.
Professor Borchgrevink, who worked as a chef and restaurant manager before becoming a researcher, said the findings have implications for both consumers and those who operate restaurants and hotels.
"Imagine you're a business owner and people come to your establishment and get a food borne illness because they didn't wash their hands - and then your reputation is on the line," he said.
"You could lose your business."
- Daily Mail