The Welsh government has launched a new campaign aimed at protecting children from second-hand smoke in cars.
Findings from the Health Behaviour in School Aged Children survey show that one in five Welsh children, aged 11 to 16, were exposed to smoke the last time they travelled in a car.
To address the issue, the government has launched the 'Fresh Start Wales' campaign, which urges parents and carers to keep their cars smoke-free.
Dr Tony Jewell, Wales' chief medical officer, said: 'Children are particularly at risk from second-hand smoke, especially in vehicles where a confined space means there is no respite from the harm of the toxic chemicals in cigarettes.
'Exposure to these chemicals puts children at risk from a range of conditions, including sudden infant death syndrome and asthma.'
Dr Jewell noted that levels of toxic chemicals are 'very high' when a person smokes inside a vehicle, even if the window is open.
The Welsh government hopes children's exposure to second-hand smoke in cars will fall within the next three years.
If this does not happen, it may consider introducing an outright ban on smoking in cars when children are present.
Wales recently introduced a ban on cigarette vending machines in a bid to make it harder for children to obtain tobacco.