London - Today’s children may be too clean for their own good, research suggests.

Evidence is growing that dirt and germs can protect against disease – and that our indoor-based, ultra-clean lifestyles are bad for our health.

It is said that without exposure to dirt and germs early in life, the immune system doesn’t learn how to control its reaction to invaders such as dust and pollen.

The latest evidence comes from Harvard Medical School researchers who studied mice kept in sterile cages and fed sterile food.

The lungs and bowels of the germ-free mice contained extra-large numbers of an immune cell blamed for asthma and bowel problems.

And when the germ-free mice developed asthma or bowel condition colitis, it was much more severe than usual, the journal Science reports.

The researchers then looked at what happened when the rodents were taken out of their sterile environment and put in bug-ridden cages with normal mice.

The adult mice did not become any less susceptible to disease, but the germ-free creatures moved in the first weeks of life became no sicker than those reared outside the sterile environment.

This suggests that there is a window of time in which exposure to bugs teaches the immune system to work properly.

Dr Richard Blumberg said: “These studies show the critical importance of proper immune conditioning by microbes during the earliest periods of life.”

But Professor Graham Rook of University College London warned skimping on cleanliness could let other, dangerous bugs take hold. - Daily Mail