The hygiene hypothesis suggests that increased disease development among children delivered by cesarean section could be the result of delayed gut colonization due to lack of contact with maternal vaginal fecal flora, resulting in an altered immune system development (2, 4, 40). Children delivered by elective cesarean section are hypothesized to have less exposure to maternal vaginal fecal flora compared with those delivered by acute cesarean section (14). Considering this hypothesis, the association between cesarean section and the development of respiratory symptoms and disorders would be expected to be stronger among those delivered by elective cesarean section, a theory not supported by the findings of previous studies or the current study. Only about 37% of children who have problems with wheezing early in life have persistent wheezing symptoms at 10 years of age (41), whereas atopic manifestation usually occurs at school age (42). Differences in the association between cesarean section delivery and asthma between age groups might therefore reflect the different asthma phenotypes (42).