Many thousands of children may have been spared serious illness and admission to hospital by the smoking ban in England, research has shown.
The ban was intriduced in 2007.
Research by a team at Edinburgh University estimates around 11,000 fewer under-15s each year are now being admitted with nose, throat and sinus problems.
Report co-author Chris Millett said the ban had a knock-on effect.
“People stopped smoking in public places, and smoking was reduced in private places as well. Parents seemed to stop smoking as much in the home, and this is where the benefit came,” he said.
Researchers analysed more than 1.6 million hospital admissions of children aged 14 and under across England from 2001 to 2012.
They found that the introduction of the smoking ban in 2007 was followed by an immediate reduction of 13.8% in the number of admissions for lower respiratory tract infections.
Admissions for upper respiratory tract infections also decreased but at a more gradual rate. The sharpest falls were seen in the most deprived children.
Dr Jasper Been, from the University of Edinburgh, who led the research published in the European Respiratory Journal, said: “Our results add to the growing body of evidence demonstrating the benefits of smoke-free legislation.
“Although our results cannot definitively establish a cause and effect, the rigorous analysis clearly shows that the introduction of smoke-free legislation was associated with significant reductions in hospital admissions among children.”
Colleague Professor Aziz Sheikh, also from the University of Edinburgh, said: “When you look at the results of this study alongside national data showing a decrease in smoking within the home, the findings greatly strengthen the recommendations for the global implementation of legislation prohibiting smoking in public places.
“We urge other nations to consider introducing and enforcing smoke-free legislation in order to protect the health of children, the most vulnerable members of society.”
In their paper, the scientists said breathing in second-hand smoke was known to increase susceptibility to bacterial or viral lung diseases such as bronchitis and bronchiolitis as well as middle ear infection.
A vast majority of the estimated 166,000 deaths worldwide each year resulting from children being exposed to second-hand smoke were due to respiratory tract infections.
Dr Carlos Jimenez-Ruiz, from the European Respiratory Society, which publishes the journal, said: “The findings of this new study add more weight to the argument that smoke-free legislation is a valuable tool in reducing the health harms of smoking, particularly in children.
“We must use this evidence to increase awareness and knowledge among policy makers of the harm caused by tobacco and the value of legislation designed to reduce this harm.”
Mike Hobday, director of policy at the British Heart Foundation, said: “These research findings provide more evidence of the health benefits of legislation to reduce the impact of smoking, specifically for young people.
“But the job is not done. We want to see the new Government take further action on smoking, including an annual levy on tobacco companies to fund tobacco control and stop smoking services to help support people to quit.
“We believe that the forthcoming introduction of standardised tobacco packaging will provide further benefits by helping to stop young people taking up smoking. Cigarette packets will no longer be the Pied Piper luring children towards this deadly habit.”