Children who are exposed to secondhand smoke when they are babies are at a higher risk of developing allergies, according to new research.
Youngsters who breath in smoke while they are infants were found to be almost twice as likely to be allergic to certain allergens, the study led by the Institute of Environmental Medicine, in Stockholm, Sweden, found.
Researchers questioned more than 4,000 families about their child's allergies, filling in a series of questionnaires until their child reached the age of four.
They were asked about the environmental factors which the child had been exposed to before and after birth, including parental smoking, animal hair and dead skin and certain foodstuffs.
A blood sample was taken from more than 2,500 children at the age of four to look for immunoglobulin E (IgE). High levels of IgE indicate a sensitivity to an allergen.
The study, published ahead of print in the journal Thorax, discovered that one parent of one in five children smoked after the birth, with around one in 20 youngsters exposed to smoke from both parents.
Around 25% of children had high IgE levels by the time they were four years old, with 15% allergic to inhaled allergens (such as animal hair), 16% allergic to food allergens and 7% to both types.
The authors concluded that children exposed to secondhand smoke early in life are almost twice as likely to be allergic to inhaled allergens, compares with who had not been exposed, and almost 50% more likely to have an allergy to foods.