Over 500 respiratory healthcare professionals have urged the government to ban smoking in cars with children.
In a letter to the BMJ, the nurses, doctors and surgeons claim that a law is needed to "protect the wellbeing of children now and in the future”.
The letter claims there is a strong consensus that exposing children to tobacco smoke is "unacceptable".
Second-hand exposure to tobacco smoke is a major cause of ill health in children, they explain.
Smoke inhalation damages the developing lung, and the Royal College of Physicians estimates that each year in the UK it is responsible for 300,000 primary care contacts, 9,500 hospital admissions, at least 200 cases of bacterial meningitis, and 40 sudden infant deaths.
Most of this additional burden of disease falls on the more disadvantaged children in society, and all of it is avoidable, they add.
Nurse Rebecca Sherrington, chairwoman of the Association of Respiratory Nurse Specialists, said: "Many people don't realise quite how serious second-hand smoke can be for children, especially in the concentrations that can build up in the car.
"Parents are often surprised that it can lead to illnesses such as ear infections, meningitis and cot death."