Smoking bans help to reduce premature births and childhood asthma, new research suggests.
A study of data from North America and Europe linked the prohibition of smoking in public places to a 10% fall in premature birth rates.
Hospital attendances for childhood asthma also dropped by the same amount in districts where smoking bans had been introduced .
Anti-smoking laws currently affect less than a sixth of the global population and 40% of children around the world are regularly exposed to second hand smoke, according to the study authors.
Passive smoking has been linked to miscarriages and premature births as well as birth defects, asthma and lung infections.
It may also contribute to the long term development of chronic conditions such as heart disease and diabetes.
International scientists conducting the new study looked at data on more than 2.5 million births and almost 250,000 hospital visits for asthma attacks.
Dr Jasper Been, from the University of Edinburgh, said: "Our research shows that smoking bans are an effective way to protect the health of our children. These findings should help to accelerate the introduction of anti-smoking legislation in areas not currently protected."
Professor Aziz Sheikh, co-director of the university's Centre for Population Health Sciences, said: "This research has demonstrated the very considerable potential that smoke-free legislation offers to reduce pre-term births and childhood asthma attacks. The many countries that are yet to enforce smoke-free legislation should in the light of these findings reconsider their positions on this important health policy question."
The findings are reported in the latest edition of The Lancet medical journal.