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."