"Indoor air pollution mainly kills mothers and children in the country both in the urban and rural areas," the ESDO, a voluntary organisation, pointed out in its study.

It said the poorest section, especially women and children, had to bear the consequences of indoor pollution "which has not been addressed adequately in the country."

Until now most research on air pollution had focused on outdoor air pollution caused by contaminants omitted by large factories and excess number of vehicles powered by internal combustion engines.

"An even more insidious killer is indoor air pollution because it silently and unnoticeably attacks people in their homes," the study said.

It suggested that simple changes in the design of homes for increased air circulation and reduced use of hazardous fuels could check the pollution to a large extent, saving the lives of a large number of people.

People need to be made aware of the hazards of indoor pollution, and simple prevention education programme can expose the silent killer and destroy its effect on the most vulnerable people, the study suggested.

The study pointed some major causes of indoor pollution which included lack of proper ventilation.

Many people have only one living space which they use as their living room, sleeping area and kitchen.

Every day cooking is mostly done inside the living space, resulting in higher carbon emissions and lower rates of oxygen replacement. Cow-dung produces methane and jute sticks produce carbon and nitrogen.

During winter season, to get respite from the cold, many people, especially in rural areas, burn wood, hay and leaves inside their living spaces without having proper ventilations.

In urban slums, due to lack of firewood, people burn plastic and rubber to keep them warm. This produces, among others, the highly hazardous hydrogen cyanide.

Extensive use of mosquito coils has also identified as a major source of indoor pollution in urban areas. The women and children, who spend more time in the home, thus are most susceptible to the perils of this indoor air pollution.

Indoor use of biomass fuels exposes household members, particularly women and young children, to enhanced concentrations of pollutants, which are much higher than concentrations in most polluted cities.

Indoor air pollution has now been recognised as a major cause of respiratory problems among children. More and more children are being born with contaminants in their bodies because of their mothers' exposure to toxins.