Being born by caesarean section greatly increases a baby's chances of developing allergies, a new study has found.

Infants delivered by C-section were found to be five times more likely than those born naturally to become allergic to common triggers such as dust mites and pets.

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 said: "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 babies. By the age of two, those born by C-section were more likely to have developed allergies to triggers such as the droppings of house dust mites, and dander, or dead skin, shed by dogs and cats.

Umbilical cord samples, breast milk and household dust were analysed, together with blood samples from both parents.

The researchers from Henry Ford Hospital in Detroit also collected information on the families' history of allergy or asthma, household pets, tobacco smoke exposure, baby illnesses and medication use. Half of all children and teenagers in the UK have experienced allergies by their 18th birthday, and each year the number of allergy sufferers in the UK increases by 5 per cent, half of whom are children.

Maureen Jenkins, of the charity Allergy UK, said: "During a natural birth the baby travels slowly down the birth canal where it ingests 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. It is immediately removed from a sterile environment, meaning the chances of developing allergy could be heightened."