People from well-educated families are almost twice as likely to suffer from some dangerous food allergies as others — possibly because their bodies’ natural defences have been lowered by rigorous hygiene and infection control, suggests a new Canadian study.

The research from McGill University also found that immigrants were about half as likely to be afflicted by the allergies, perhaps reflecting differences in diet and environment between their countries of origin and Canada.

The study, just published in the Journal of Allergy, was meant to address an enduring medical mystery: Why have so many people in certain industrialized countries developed violent reactions to peanuts, shellfish and other foods in recent decades?

The link to higher education may be explained by what is called the hygiene hypothesis, the unproven idea that smaller families, cleaner homes, more use of antibiotics to treat infections and vaccines to prevent them have curbed development of the immune system, said Dr. Moshe Ben-Shoshan, who led the research. That in turn could make some people more susceptible to allergy.

If the hypothesis does actually explain some food reactions, though, parents may not be able to do much about it, admitted the allergist at Montreal Children’s Hospital. The benefits of such health products as antibiotics and vaccines easily outweigh the risk of children developing serious allergies, said Dr. Ben-Shoshan.
“We can’t suggest we become dirtier and expose our children to more bacteria,” he said. “If the price of having fewer allergies is more infection, I don’t know any parent who would expose their child to more infection.”

The study’s findings are far from conclusive but they, and the hygiene hypothesis as an explanation, seem plausible, said Dr. Stuart Carr, president of the Canadian Society of Allergy and Clinical Immunology. He also cautioned, however, that translating the knowledge into preventive action would be complicated.