The fumes from household cooking fuels pose a huge and largely unrecognized health hazard to inhabitants, especially women and children -and India, with its huge rural population, suffers an inordinate number of deaths from cooking fumes. As Anjana Pasricha reports from New Delhi, health campaigners say rural households must switch to cooking stoves that cause less pollution.

It is a common sight across Indian villages: women cooking the family meal on traditional stoves that burn wood, leaves or animal dung.

Few people - including the women themselves - realize that the black, acrid smoke that billows from these kitchen fires is a silent killer.

Scientists say the fuel in primitive stoves fails to burn completely, and produces poisonous pollutants such as carbon monoxide. Those who inhale this smoke regularly become vulnerable to acute respiratory ailments such as asthma, chronic bronchitis, and can even develop tuberculosis and lung cancer.

The World Health Organization says the scale of the problem is massive in India, where 650 million people depend on cheap fuels for cooking.

The National Officer for Sustainable Development at WHO's India office, A.K. Sengupta, says household smoke claims tens of thousands of lives across the country, mostly in poor rural homes.

"Indoor air pollution is almost four, five times more problematic than outdoor air pollution, and there are almost 400,000 deaths per year due to indoor air pollution," Sengupta said. " The rural population is quite big and alternate fuels are not easily available."

The WHO says India accounts for roughly one-third of the one and a half million deaths caused worldwide by use of cheap cooking fuels every year.

Most of the victims are women and children because women traditionally do the cooking, and children stay at home with them. In fact mothers often cook with babies in their arms, exposing the infants directly to the toxic smoke.

Health campaigners say the best way to reduce the hazard is to provide poor communities with improved stoves that give out fewer emissions.

A handful of government-sponsored programs to design and distribute such stoves have been undertaken, but they have met with little success so far.

For example a project in Maharashtra state to distribute pollution-reducing stoves to rural homes flopped. Village women simply discarded the stoves, known in India as "chullahs."

Rashmi Patil, a professor at the Center for Environmental Science and Engineering at the Indian Institute of Technology in Mumbai, explains why rural communities rejected the chullahs.

"The scheme is not very popular, it was not very successful…the villagers are reluctant to use them because they are not trained how to use them," Patil said. "Suppose some part goes out, their own chullahs they can repair, but these chullahs, the parts are not available, they cannot repair it themselves…. The benefits of the chullah was not explained to them, no training was given to them on the maintenance of the chullah."

Patil says experts are trying to rectify these problems by designing stoves that are easy to maintain. They are also launching education programs to raise awareness about the need to switch to better stoves.

Some voluntary agencies have also undertaken initiatives to design less-polluting stoves.

The Shell Foundation, a Britain-based charity organization, is working with local groups in India to develop and market clean cooking stoves for rural communities.

The director of the Shell Foundation, Kurt Hoffman, says the stoves are being sold, not distributed free of cost, because the profit motive ensures that a viable product is developed for the consumer. He says the foundation is involving local markets and women's groups to reach village homes.

Hoffman says the program began three years ago, and has begun reaching rural communities in several parts of the country.

"It is a trial-and-error process, so in the early stages we found or our partners found that there were lots of complaints, and the stoves were rejected," explained Hoffman. "Over time, the products have become better. There is a particular product similar to a pressure cooker almost that has been fantastically successful."

However, the need is so huge that such initiatives cannot meet the demand. For example, Shell has sold about one hundred thousand stoves in Maharashtra state - but the need is for 10 million.

Experts say in the long run, countries like India must move to using cleaner fuels - but given the massive poverty, this could still be decades away.