Constant wiping and sterilising undermines this phenomenon and may mean increased allergies. In Britain, which spent 610 million pounds on household cleaning products last year, there was an exponential growth in allergies. Studies have shown that children raised on farms are less likely to get allergies, asthma and eczema because they inhale all kinds of toxins and drink raw milk packed with bugs. Youngsters raised with cats or dogs also seem to be protected.
Scientists believe the theory, which they call the hygiene hypothesis, could also explain rising incidence of cancer.
According to the hypothesis, repeated exposure to allergens, bacteria or certain toxins keeps the immune system on 'red alert', suppressing cancer cells in the earliest stages of development.
Studies suggest that the more germs you get into your body, the less likely you are to get certain tumours.
As far ago as the Seventies, it became clear that cotton industry workers were less at risk of lung cancer than other occupations. The reason behind it is a bacterial endotoxin that contaminates raw cotton and the dust it gives off. This toxin constantly stimulates the immune system to be on guard for abnormalities.
Childhood leukaemia presents the most compelling evidence about how germs can protect us against cancer. Experts think children who attend day care facilities in the first few months of life may gain protection against the disease.
This is because they are exposed to a range of different organisms at a time when the immune system is still developing. With the immune system permanently active, the chances of leukaemia developing may be reduced.
But, the timing is crucial. If this encounter with the bacterial 'enemy' happens in the first few weeks of life, the immune system is gently 'prodded' into action. If it happens a year or more after birth, it triggers an overreaction by the immune system so destructive it sparks the growth of cancer cells, Daily Mail reported.
Further evidence came from the unification of Germany in the early Nineties. In East Germany, hygiene standards were comparatively poor, yet childhood leukaemia rates were low. After unification, hygiene improved and leukaemia rates rose to reach levels seen in the West.
This theory about infection and cancer is not new. Over a hundred years ago, an American doctor called William Coley came up with a controversial treatment that involved injecting a cocktail of bacteria straight into the tumour, in a bid to trick the immune system into thinking it was under attack from foreign organisms.
It worked. The first patient to be treated, in February 1893, was a 16-year-old boy with a huge abdominal tumour. After seven months of treatment, the cancer vanished.