Allergic children living in affluent countries were four times as likely to have the lung condition as their non-sensitized counterparts; in non-affluent countries, children with allergic responses were only 2.2 times as likely to have asthma.

The global research study is based on 54,000 parental assessments of their children's respiratory symptoms, gleaned through standardized questionnaires. The children studied were between eight and 12 years old.

Researchers also evaluated 31,000 skin-prick tests and analyzed the serum levels of allergen-specific IgE in nearly 9,000 children from 22 countries, from rural Africa to urban Europe.

The allergen-specific IgE antibody test screens for an allergy to a specific substance or substances when a person suffers from allergy-like symptoms.

Researchers then assessed how the severity of allergic sensitizations and asthma symptoms of a given country were connected to its gross national income per capita.

"We observed large variations in the prevalence of asthma symptoms and of atopic sensitization (allergic sensitivity) among populations," Dr. Gudrun Weinmayr, one of the study's authors, said in a release.

"The association between current wheeze, an indicator of asthma, and skin prick sensitivity, an indicator of allergic reaction, was strong in virtually all affluent countries, but much weaker in less affluent settings."

The study's authors theorize that local environmental factors may affect asthma and allergy rates in different ways. And they speculate that developed countries may have more cases of allergy-induced asthma while less-affluent nations have more cases of non-allergic asthma in children.

They also believe that some of the factors that prevent children from developing asthma may be absent in more affluent countries. "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," reads the report.

According to a 2006 report by the Montreal-based Commission for Environmental Co-operation, asthma rates among children in some parts of North America are four times higher than they were 20 years ago.

It found that in Canada, about 20 per cent of boys and 15 per cent of girls aged eight to 11 have been diagnosed with asthma.