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She says: "Our study, which followed babies from the prenatal period forward, showed that infants born by C-section, if exposed to common environmental allergens (dust mites, dogs, cats and cockroaches), were more likely to become sensitised to those allergens by two years of age.
"We found that babies born by C-section, if exposed to an allergen, were eight times more likely to be sensitised to dog allergen.
"Sensitisation means you have antibodies to the allergen, which is a prerequisite to developing a clinical allergy associated with that allergen.
"They were five to six times more likely to be sensitised to dust mite allergen, and almost twice as likely to be sensitised to cat allergen.
"We know that babies born by C-section take a longer time to assemble a normal gut bacterial ecology, and that ecology is critical in early immune system development.
"We hypothesise this delay makes them more susceptible to becoming sensitised."
Dr Christine Cole Johnson, from the Henry Ford Hospital in Detroit