A new study shows that children who regularly breathe in second-hand smoke as infants are almost twice as likely to develop allergies.
The findings come from research headed by the Institute of Environmental Medicine, in Stockholm, Sweden, which involved more than 4000 families.
Parents were interviewed about their children's allergies and asked to fill in questionnaires when their child was aged two months, 12 months, two years and four years.
The questionnaires included questions about various environmental factors to which the children had been exposed before and after birth. These factors included cigarette smoke, pet dander (animal hair and dead skin) and certain foods with high allergenic potential such as wheat, cow's milk and peanuts.
Information on other factors that can affect allergy incidence was also gathered. Data on the outdoor air pollution the children were exposed to was extrapolated from levels of vehicle and industry pollutants known to be present where each child lived. Socioeconomic factors were also taken into account with parents asked to complete employment and education histories. In addition the parents were asked about their own history of allergic diseases.