Caesarian birth greatly increases a baby’s chances of developing allergies, a study has found.
Infants delivered by C-section are five times more likely than those born naturally to become allergic to common triggers such as dust mites and pets, according to the research.
Scientists believe the babies are left vulnerable by avoiding the journey through the birth canal, which would normally expose them to their mother’s bacteria.
The discovery lends support to the “hygiene hypothesis” that links childhood allergy to over-clean conditions early in life.
Lead researcher Dr Christine Cole Johnson, from the Henry Ford Hospital in Detroit, US, said: “This further advances the hygiene hypothesis that early childhood exposure to micro-organisms affects the immune system’s development and onset of allergies.
“We believe a baby’s exposure to bacteria in the birth canal is a major influencer on their immune system.”
Dr Johnson’s team studied 1,258 newborn babies and assessed them when they were one month, six months, one year and two years old.
By two years of age, babies born by C-section were much more likely to have developed allergies to triggers in the home such as the droppings of house dust mites, and dander, or dead skin, shed by dogs and cats.
Umbilical cord and stool samples from each baby were analysed, together with blood samples from both parents, breast milk and household dust.
Information was also collected on every family’s history of allergy or asthma, household pets, tobacco smoke exposure, baby illnesses, medication use, and aspects of pregnancy.
The results of the research were presented today at the annual meeting of the American Academy of Allergy, Asthma and Immunology in San Antonio, Texas.
Half of all children and teenagers in the UK have experienced allergies by their 18th birthday.
Each year the number of allergy sufferers in the UK increases by 5%, half of whom are children.
An estimated 21 million UK adults have at least one allergy. Ten per cent of children and adults under the age of 45 have two or more allergies.
Maureen Jenkins, director of clinical services at the charity Allergy UK, said: “During a natural birth the baby travels slowly down the birth canal where it ingests normal bacteria, which has been shown to aid a healthy immune response and protect against allergy.
“In the case of a Caesarean section, the baby has no contact with the birth canal. Instead it is immediately removed from a sterile environment, meaning the chances of developing allergy could be heightened.”