Babies born via C-section may be missing out on vital bacteria that make them less likely to develop allergies and asthma later in life, according to a study.

The research, published in the American Journal of Epidemiology, studied 6,157 infants born in New York and tracked their health over three years.

The report found that infants delivered by C-section were at more than double the risk of developing food-borne allergies and asthma by their third birthdays than babies born vaginally.

With vaginal birth rates decreasing globally, the results could be an important consideration for expecting mothers, said Erin Bell, a professor of environmental health sciences at University at Albany.

“Though cesarean deliveries simply cannot be avoided in many cases due to the health of the mother or baby, this study provides additional data that when vaginal delivery is safe, it provides additional health benefits for the infant,” Bell said in a statement.

Experts have long suspected that bacteria passed from mother to baby during vaginal birth – a process known as “microbiome seeding” – could play a role in protecting children.

The new study found that babies born via emergency C-section were significantly associated with wheezing and food allergies.

The findings suggest that babies born via C-section “miss out” on the important bacteria, thereby increasing their risk, Bell said.

“We expected that planned cesarean delivery would be associated with these outcomes since babies delivered by unplanned or emergency cesarean deliveries may have some exposure to the bacteria in the birth canal. Thus, our findings for emergency cesarean deliveries were unexpected,” she said.

Previous studies have pointed to other factors, such as maternal obesity or sterile birthing environments, that increase the risk of asthma and allergies. Bell’s study found that mothers who gave birth via C-section were more likely to be overweight, obese and over the age of 30.

Mothers who gave birth vaginally were also more likely to breastfeed their babies in the first year, compared to mother who gave birth through C-sections.


An Australian study published last year in the journal Birth found that children who had a vaginal birth had fewer short- and long-term health problems than those born via C-section.

The study, which drew data from nearly healthy 500,000 women and their children, found connections between after-birth interventions and higher risks of respiratory infections, metabolic disorder and eczema.

Babies born by emergency C-section also saw higher rates of metabolic disorders, such as diabetes or obesity, according to the study.

Microbiomes also appear to play a role in the womb. A study published in 2014 found that, contrary to popular belief, placentas are not a sterile environment but are actually rich in good germs. Researchers said the findings suggest that microbes begin to play an important factor for developing healthy fetuses long before birth.