Lady Macbeth, long after she had washed her hands dripping with Duncan’s blood, continued to be preoccupied by hand-washing. So great was her sense of guilt that no amount of water and the ritual incantation of “Out, damned spot! out, I say” could restore her peace of mind or ability to sleep.

Compulsive handwashing in those who are either guiltridden or suffer from obsessive compulsive disorder has intrigued generations of psychiatrists. Obsessions are persistent anxieties, impulses and ideas, including feelings of guilt, that are as intrusive as they are senseless. Compulsions refer to ritualistic, repetitive behavioural patterns that obsessed people adopt. Hand-washing, a vain attempt at ridding body and mind of the evidence of some real or imagined guilt, is a common example of compulsive behaviour.

Chen-Bo Zhong and Katie Liljenquist, two research workers at the University of Toronto, have also recently been preoccupied with hand-washing. Their studies have shown that the Macbeth hand-washing syndrome is not confined to those with classic obsessive compulsive disorder or to others as disturbed as Lady Macbeth was after committing regicide.

Mr Zhong has shown that the Macbeth instincts are still with us modern sinners and we behave in a way that Lady Macbeth would have understood. Without understanding our motivation, we use soap and water or a shampoo to erase guilty stains from our consciences. After sexual misdemeanours, a minor unethical action at work or some mean social act we will bath in exotic oils, wash our hair with luxurious shampoo or indulge in other forms of symbolic cleansing.

The Toronto research workers demonstrated a subtle manifestation of the Macbeth syndrome. Apparently, theatre showers are not much used after a performance. Actors usually wash, remove their make-up, change and then either go home or out to dinner. However, when Macbeth is being played, Mr Zhong and Ms Liljenquist found that a cast that has recently been playing their murderous roles are likely to shower before they leave a theatre.

The research also showed that penance isn’t dead. Students, for example, who worry about adolescent indiscretions that they now consider sinful are those most likely to volunteer for good works when at a university.

Mr Zhong is not the only person interested in hand-washing. Cleanliness in hospitals is now accepted as being essential but inadequate. Anyone visiting a patient in hospital has a sense of guilt if they don’t use the alcohol-based liquids to wash their hands before and after entering the ward and would feel as unclean as if they had gone to bed without brushing their teeth if they didn’t wash their hands thoroughly before and after touching a patient.

Professor John Oxford is chairman of the Hygiene Council and is touring the world spreading the message of cleanliness. He emphasises that household hygiene is as important as hospital cleanliness: in both places we need to return to the standards that would have satisfied the strictest prewar school matron or Nightingale-trained nurse. More than 80 per cent of all food poisoning is caught at home rather than in a restaurant. There is a 60 per cent chance that once salmonella or campylobacter has struck one member of a family it will spread to others in the house.

Disinfectants are back in fashion. Dettol or some similar product should be used to wipe down all the surfaces in the kitchen and bathroom to help to break the chain of infection. Hands must not only be washed after going to the lavatory but invariably before meals or after sneezing or coughing. It should be unthinkable to handle food without washing your hands.

It shouldn’t be a token dip, but medicated soap should be used and the wash should last as long as it takes to sing the refrain Happy Birthday twice.