The notion of exposing young children to infections in a bid to protect them from later allergies¹ is wrong, latest research suggests.

最新研究显示，将幼童暴露于传染环境中以防止他们将来过敏的做法是错误的。

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Catching infections early on in life may do no good

The decades-old "hygiene³（卫生） hypothesis" holds that early exposure to microbes（微生物） somehow challenges the immune system and strengthens it against allergies.

Studies have shown children exposed to bugs⁴ by older siblings⁵ or attending nursery cut their future allergy⁶ risk.

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

No benefit

The study by Dutch investigators⁷ 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 asthma⁸（哮喘） or another allergy（敏感，反感） by the age of eight.

The children who went to nursery and who had older siblings had more than quadruple（四倍） the risk of frequent chest infections and double the risk of wheezing⁹（喘息） 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（呼吸的） morbidity¹⁰（病态） 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 Forum¹¹ 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 mollycoddling¹²（女性化的男人，娇生惯养的男人） our children a little too much.

"But allergies run in families. In susceptible¹³（易受影响的） 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."