More than 600,000 people, including 165,000 children, die every year from passive smoking, a report from World Health Organisation experts says today.
The estimates from the first analysis of the true global toll are based on the best available data across 192 countries and the known effects of exposure.
The biggest impact on children is in the developing world. "Two-thirds of these deaths occur in Africa and south Asia," the authors write in the medical journal The Lancet. "Children's exposure to second-hand smoke most likely happens at home.
"The combination of infectious diseases and tobacco seems to be a deadly combination for children in these regions and might hamper the efforts to reduce the mortality rate for those aged younger than five years as sought by Millennium Development Goal 4 [to reduce the mortality rate among the under fives by two thirds ]."
In 2004, the most recent year with comprehensive data, passive smoking is estimated to have caused an estimated 379,000 deaths from ischaemic heart disease, 165,000 from lower respiratory infections, 36,900 from asthma and 21,400 from lung cancer - around 1% of deaths worldwide.
Women die in larger proportions than men or children - 47% against 28% in children and 26% in men. Fewer women smoke than men and they are more likely to be exposed to second-hand smoke.
Children are unable to escape second-hand smoke at home. They are more likely than adults to suffer health damage from passive smoking, such as asthma or breathing problems.
The authors, most of whom work for the WHO's Tobacco Free Initiative, point out that only 7.4% of the world's population live in countries with laws to prevent smoking in public places - which safeguard non-smokers and send out strong messages about the dangers and anti-social nature of cigarettes. They recommend immediate enforcement of WHO's Framework Convention on Tobacco Control, which includes higher tobacco taxes, plain packaging and advertising bans.
To protect women and children, they say that education campaigns on the dangers of indoor smoking are needed.
In a commentary, Dr Heather Wipfli and Dr Jonathan Samet from the department of preventive medicine at the Keck School of Medicine of the University of Southern California, say the research shows the crucial need to empower women, especially in countries where smoking among men is increasing.
"If empowered, women can have a key role in protecting themselves, their children and other family members from this exposure," they write, calling for gender-sensitive education programmes and encouragement to women to take leadership roles in health.
