“Our findings suggest that urban living is an independent risk factor for developing infections in early life when taking account of several related factors such as exposure to air pollution and starting day care. Interestingly, changes in the blood of pregnant mothers and newborn babies, as well as changes in the new-born immune system, seem to partly explain this relationship,” said Dr Nicklas Brustad, a researcher and physician on the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) based at Gentofte Hospital and the University of Copenhagen, Denmark.