As many as one billion people, mostly women and children, are regularly exposed to levels of indoor air pollution exceeding WHO guidelines by up to 100 times. This startling statistic was quoted at a WHO strategy meeting on Air Quality and Health held in Geneva this week.

Air pollution is a major environmental health problem affecting both developed and developing countries. This is a truly global concern involving ambient air quality in cities as well as indoor air quality including the workplace, in both rural and urban areas. The highest air pollution exposures occur in the indoor environment particularly in developing countries. Cooking and heating with solid fuels, that is wood, coal, dung, crop residues and charcoal, still occurs for over half the world's population. A deadly combination of solid fuels, inefficient stoves and poor ventilation triggers off a complex mix of health damaging pollutants in homes.

In India, where 80% of households use solid fuel, there are estimates that half a million children die annually from indoor air pollution, especially from acute respiratory infections. The figure for sub-Saharan Africa is roughly the same. In Latin American countries, where one quarter of households use solid fuels, an estimated 30 000 people die each year from acute respiratory infections attributable to indoor air quality.

So much about the myth of clean country air. In fact, nearly three-fifths of the total global exposure to particulate matter, one of the most ubiquitous air pollutants, occurs in the rural areas of developing countries. Worldwide, this translates into as many as three million deaths a year.

As always seems to be the case, it is the world's poorest people who suffer most. As a rule, they face a cocktail of risk factors of which air pollution is just one; others include malnutrition, unsafe water and poor health care infrastructure. Malnutrition, unsafe water and use of solid fuels indoors together cause over one quarter of all deaths in the least developed countries.

Children are of particular concern. They are especially vulnerable to high levels of air pollution. The Global Burden of Disease study conducted by WHO in 1990, has clearly shown that 30% of the estimated number of deaths from all diseases occur before 15 years of age, but for acute respiratory diseases, the figure is twice as high. A WHO Task Force on the Protection of Children's Environmental Health has been created to address these problems.

Despite increasing knowledge about harmful health effects of air pollution, preventive action is often slow to follow. "WHO would like to provide its 191 Member States with irrefutable evidence that air pollution causes disproportionately heavy burden of disease," explains Dr Michael Repacholi, WHO Coordinator, Occupational and Environmental Health. "We'd like to provide them with a sound environmental policy framework and actions applicable to different settings and to different socio-economic conditions. In short, we'd like to provide them with a proper strategy to eliminate avoidable air pollutants and thus reduce this disease burden in a cost-effective way."

This week's meeting in Geneva identified major peaks to be scaled on the way to creating a WHO strategy on air pollution and health. In public health terms, air pollution is not an exact science. Often, health effects that may be attributable to air pollution can also be closely linked to other risk factors. That is why establishing a health effects database on air pollution is seen by WHO as an important stepping stone towards achieving these goals. But first, all parties involved should hammer out a unified methodology for collecting comparable data world wide to support sound, science-based assessments of health impacts.

The database will help to identify hotspots of health-threatening air pollution levels and populations of high risk. It will also help keep track of major sources of pollution and their effect on public health. Economic costs to society and individuals of health impairment due to air pollution, as well as cost-effective intervention strategies, will also be addressed by WHO.