Dr. Derek G. Cook of the University of London and colleagues note in the journal Allergy that the so-called hygiene hypothesis, as originally proposed, holds that infections caught from older siblings protect against hay fever. A number of studies have suggested an association between early infections and reduced likelihood of allergies.
In the current study, the researchers used general practice databases to identify 3 549 pairs of hay fever sufferers and matched "controls," and tried to determine associations between 30 different types of infection and risk of hay fever development.
Upper respiratory tract infections, diarrhoea and vomiting, and acute earache in infancy were each related to a moderately increased risk of hay fever, the researchers report.
However, the picture changed when the results were adjusted for how often the children saw a doctor - because children with more doctor visits were more likely to have infectious diseases recorded and also more likely to be diagnosed with hay fever.
The only condition that remained significant was bronchiolitis, or inflammation of the small airways, and this condition was linked with a 20 percent reduction in risk of hay fever.
"Except for bronchiolitis, possibly a chance finding," the researchers conclude, "none of the clinically apparent infections considered appear to have an important role in allergy prevention."