The report, published in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine, said children with allergic sensitizations in economically developed countries are much more likely to develop asthma than similarly sensitized children in poorer countries.

The researchers speculated a possible explanation could be that some factors that protect children with allergic sensitization from developing asthma are less present in affluent settings, or that acquired commensal bacteria play a role in development of tolerance and immune function.

"A wide range of different factors, including nutrition, microbial and allergen exposure, housing conditions, and exposure to pollutants, and so forth, may have played a role," the report said.

An international team led by Dr. Gudrun Weinmayr of the Institute of Epidemiology of Ulm University in Germany found that children living in affluent countries with allergic sensitizations were four times as likely to have asthma as their non-sensitized counterparts. In non-affluent countries, children with allergic responses were only 2.2 times as likely to have asthma.