According to researchers, exposure to bacteria in the vagina during birth may play a key role in priming the immune system, providing a defence against the development of allergies.
In case of Caesarean kids, exposure to bacteria happens later and research has shown they have different intestinal flora - gut bacteria - suggesting the maturation of their immune systems is delayed, reports the Independent.
In the study of almost 3,000 children, birth by Caesarean was associated with an 80 percent increased risk of asthma by age eight compared with vaginal birth.
Among the one in 10 children with two allergic parents, the incidence of asthma was three times higher among those born by Caesarean.
These children have a strong inherited predisposition to the disease.
Caroline Roduit of the National Institute for Public Health in Bilthoven, the Netherlands, who led the study published in Thorax, said: "The increased rate of Caesarean section is partly due to maternal demand without medical reasons.
In this situation the mother should be informed of the risk of asthma for her child, especially when the parents have a history of allergy or asthma."