Page last updated at 10:31 GMT, Tuesday, 8 September 2009 11:31 UK

Infection-allergy link questioned

Girl with a cold
Catching infections early on in life may do no good

The notion of exposing young children to infections in a bid to protect them from later allergies is wrong, latest research suggests.

The decades-old "hygiene hypothesis" holds that early exposure to microbes somehow challenges the immune system and strengthens it against allergies.

Studies have shown children exposed to bugs by older siblings or attending nursery cut their future allergy risk.

But new work published by the American Thoracic Society casts doubt on this.

No benefit

The study by Dutch investigators at the Erasmus University found although children in day care got more colds and other infections, they were just as likely as other children to go on to develop asthma or another allergy by the age of eight.

There is some truth in the hygiene hypothesis
A spokeswoman from Allergy UK

The children who went to nursery and who had older siblings had more than quadruple the risk of frequent chest infections and double the risk of wheezing in early life, with no obvious pay off in terms of later protection from allergy.

The infections may, therefore, do more harm than good, contrary to common belief, the authors told the American Journal of Respiratory and Critical Care Medicine.

Lead author of the study on 4,000 children, Dr Johan de Jongste, said: "Early day care should not be promoted for reasons of preventing asthma and allergy.

"Early day care merely seems to shift the burden of respiratory morbidity to an earlier age where it is more troublesome than at a later age."

Other experts have questioned if we need exposure to dirt and germs to build a balanced and healthy immune system.

Too clean?

Experience shows children who grow up on farms are less likely to develop allergies like hay fever and asthma.

And there is the belief that too much cleanliness is not a good thing, and our excessive use of disinfectant products is partly to blame for the recent allergy boom.

But Professor Sally Bloomfield from the International Scientific Forum on Home Hygiene disagrees. She said: "There is no evidence at all for this. However much we clean our homes we are still constantly exposed to microbes."

A spokeswoman from Allergy UK said: "There is some truth in the hygiene hypothesis. Certainly, little Johnny playing in the mud and growing up on a farm may be more healthy than other children. And we are probably mollycoddling our children a little too much.

"But allergies run in families. In susceptible individuals, there is something in their environment that triggers the allergy. For asthma, that could be a dusty home."

Dr Elaine Vickers of Asthma UK said: "The hygiene hypothesis is a hot topic of debate in the research community.

"Whatever the truth, the best advice we can currently give to parents is not to smoke around their children and make sure they have a balanced diet and get plenty of exercise."

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