Exhortations to wash your hands more are a major plank in the efforts to stop swine flu, but how much does it really help?
We have been warned to make sure we wash our hands properly to stop the spread of swine flu.
The government's adverts show the disease spreading quickly by touch.
Sneeze into your hands, they suggest, and you will leave highly infectious fingerprints everywhere you go.
It is a scary prospect. But there is something we can do, the adverts tell us.
Use a tissue, throw it away, and then wash your hands. Catch it, bin it, kill it, as the posters say.
But even though ordinary flu is a common illness, scientists are not in agreement about exactly how it - or swine flu - is spread.
The government's position, as stated on the DirectGov website is: "To reduce the risk of catching or spreading the virus you should... wash your hands regularly with soap and water."
But there is no evidence that hand washing reduces the spread of swine flu, according to an epidemiologist at the London School of Hygiene and Tropical Medicine, Wolf-Peter Schmidt.
"There have been a small number of trials in schools. I would rate that two of these trials have been of good quality and both these studies do not show any effect on respiratory illnesses in general."
He said laboratory experiments on the common cold have been interesting but, in terms of flu, are not conclusive.
"It was shown that the common cold virus can be spread from surfaces and fingers to people if they touch their eyes, and they can then become affected with the cold. This has not been shown for flu.
"The fact it's been shown for one respiratory virus may suggest that it also works this way for influenza. But that has never been shown in the lab or the real world."
He said there is more evidence that flu mainly spreads when we talk, cough and sneeze.
But the Department of Health has said it is satisfied there is enough evidence to suggest flu is spread through direct contact.
"Several studies have documented both the major contribution played by contaminated hands in the transfer of infection and the effectiveness of hand hygiene in healthcare and community settings," a spokesperson says.
"At least one study has demonstrated that influenza virus is readily inactivated within 30 seconds by a commercially-marketed alcohol hand disinfectant, following experimental contamination of hands."
Dr Schmidt is concerned about the quality of studies in this area.
But even if you were to accept the studies were inconclusive, there are those who say the circumstantial evidence in favour of hand washing is overwhelming.
Common sense tells you hand washing will ward off flu, said John Oxford, professor of virology at St Bart's and the Royal London Hospital.
"No one's done the billion pound experiment where you infect somebody deliberately," he says. "But I don't think it's necessary. I wouldn't put money into that at this stage. I would go with all the circumstantial evidence.
"When you've got flu, you're awash with virus. People shield their coughs and get it on their hands. Then we know the virus can hang around for a few hours."
It's a simple jump to see that people then shake hands or have other contact, with the recipient scratching eye or nose and becoming infected.
"So it's circumstantial evidence but overwhelming. I don't think anyone would dispute it now," says Prof Oxford.
And in any case while there might be those who dispute the strength of the link between swine flu and hand hygiene, the government's campaign still would have positive effects.
Dr Schmidt believes that if you take care to wash your hands because of swine flu , you might be doing more to protect yourself against any stomach bugs going round.
"It has to be said that the evidence that hand washing can reduce gastro-intestinal infections is better," he says.
But is the threat of swine flu making us wash our hands more?
Researchers at the London School of Hygiene and Tropical Medicine are running an experiment in a service station to count the number of people who wash their hands.
They have got an infra-red beam on the door to the toilets, and sensors on the soap dispensers. The results are automatically sent to their computers.
In 2008 about 30% of the men visiting the facilities used the soap dispensers, while last year, when the experiment re-started six weeks after the pandemic in Mexico, hand washing was at 45%, Dr Schmidt notes.
"Hand washing then went up throughout July and August, and peaked at 57%."
A comparison of the results of the hand washing study with hospital admission rates for gastro-intestinal diseases could be interesting, Dr Schmidt believes.
He would not be surprised if we see less of the winter vomiting bug.
"Norovirus causes quite nasty diarrhoea and vomiting, and there exists quite good evidence that it is transmitted by touching surfaces and not washing hands."