Babies exposed to secondhand smoke in early infancy are more than twice as likely to develop some allergies, research has revealed today.

Swedish scientists found that children had double the risk of being allergic to inhaled allergens, such as pet dander (animal hair and dead skin), compared to those who had not been exposed.

Children who breathed in secondhand smoke were also 50 per cent more likely to be allergic to foodstuffs.

The researchers surveyed 4,000 families about their children's allergies and environmental factors, such as smoking, that they had been exposed to before and after birth.

Each participant was questioned when children were two months old, one year old, two and four.

A blood sample was taken when the children were four to assess the level of an immune system chemical, IgE, that is released in response to allergic substances or allergens.

One in 12 participating mothers smoked throughout pregnancy and one in eight smoked during part of their pregnancy.

About one in 20 children were exposed to smoke from both parents; one parent of a fifth of children smoked after their baby was born.

Writing in the journal Thorax, the researchers say the effects of secondhand smoke were "consistent and strong".

Amanda Sandford, research manager of the health campaigning charity Ash, said the research provides extra evidence that families should make their homes smokefree to give their children the "best possible start in life".

"This study provides yet more evidence of the need to ensure that babies and young children are not exposed to tobacco smoke," she added.

"While the development of some allergies may not be fully understood, this research shows that one way of substantially reducing the risk is by banning smoking in the home."

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