Newborn babies are at risk of suffocating if left in their car seat for a journey lasting more than 30 minutes, researchers warn.
Doctors say very young babies whose neck muscles are not strong enough to stop their heads falling forward during a car journey, could stop breathing if in a car seat for too long.
Dr Peter Fleming, a paediatrician at Bristol University, carried out research in a laboratory to simulate the effect of a baby sleeping in a car seat during a car journey at 30mph. After 30 minutes, the amount of oxygen in the blood of babies under two months, had fallen significantly.
Dr Flemming, who helped stem a cot death epidemic (sudden infant death syndrome) by discovering that babies would have a better chance of survival if they slept on their backs, is now advising that babies should travel in a properly secured child seat for a maximum of 30 minutes.
He says an adult should sit next to the baby to make sure they are breathing properly.
Dr Flemming also advises that parents "try to avoid unnecessary car journeys for babies".
Researchers conducted the study at Swindon's Great Western Hospital where they discovered putting babies in an upright position could cause breathing difficulties.
Manufacturers currently advise that babies are not left in their car seats for more than two hours.