Maksudum Bibi, a housewife from the village of Abdalpur north of Calcutta, coughs furiously and is almost in tears as she lights up her traditional cooking stove.
Rural women breathe in the equivalent to 20 cigarettes a day, researchers say; Pictures: Sudipto Das/Con Images
Known locally as chula, the stove uses firewood or cakes made of cow-dung for fuel.
"I am unable to breathe properly whenever I use the chula," she says. "But I have been using it for over 20 years. It is the only thing I have with which to cook".
Maksudum Bibi probably has no idea that she has spent these 20 years with an invisible but deadly companion.
Three months back, a group of scientists from the Calcutta-based Chittaranjan Cancer Research Institute (CCRI) did a thorough check-up on Maksudum Bibi and many other rural housewives who use the chula, as part of a study on indoor pollutants in rural areas.
"This chula is a silent killer. These women are actually inhaling pollutants equivalent to as many as 20 cigarettes everyday," says CCRI's Manas Ranjan Roy.
Dr Roy was part of the team that conducted the study under Twisa Lahiri, the director of the institute.
Another study in Bangladesh, funded by the World Bank, has come to a similar conclusion.
"The choice of fuels makes a difference in the levels of pollution," says Mainul Haq, part of the Bangladesh research team.
"Natural gas and kerosene are significantly less polluting than biomass fuels (fuels from plant material, vegetation or agricultural waste)."
The findings of both the studies are deadly.
Pollutants from biomass fuels used indoors are responsible for 1.6 million deaths in developing countries around the world, the researchers estimate.
India accounts for nearly one-third or some 550,000.
While scientists have mostly concentrated on the dangers of outdoor pollutants such as emissions from factories or vehicles, these two studies are focussed on indoor pollutants like those from the chula.
"Our study will dispel the false impression that outdoor pollutants are the major killers," says Dr Roy.
Most poor people in rural South Asia use biomass fuels. It accounts for 80% of the energy supply for rural households in India.
And the picture is not very different elsewhere in the region as well across most of the developing world.
Researchers say indoor pollution can be as deadly as outdoor pollution
"There is a misconception that our cities are death-traps while the villages are idyllic havens," says Dr Roy.
"Indoor pollution in rural households is as deadly as urban pollution".
Biomass fuels emit deadly gases that increase the risk of acute respiratory infections, leading to bronchitis and even cancer.
These apart, other ailments such as sinusitis, coughing and headaches are more common among women who use the chula.
According to the Indian Central Pollution Control Board norms, the maximum permissible limit for pollutant particles is 60 micrograms per cubic metre. But the samples collected by the CCRI from rural households contained 2,000 to 5,000 micrograms of pollutants.
The situation is alarming but these researchers say a cure exists.
According to Dr Roy, those suffering from such pollutants have two options. "They can either switch over to liquefied petroleum gas (LPG) or make arrangements for proper ventilation in their kitchens," he recommends.
Switching over to LPG, however, is a costly proposition in countries such as India. Prices continue to rise, which means safer ventilation may be more viable.
Meanwhile, some help may be on the way from the Indian pollution control authorities that have recently started to take note of the menace.
"We are alarmed," says Shyamal Sarkar, secretary of West Bengal Pollution Control Board. "And as an immediate measure, we are planning to launch a programme to make the poor aware of this hazard".
State governments in India should look at these studies and start encouraging villagers to use cleaner fuels, he says.
But the more time the authorities take to implement the changes, more people will continue to die.