As societies modernize, households move up the ‘energy ladder’ to cleaner liquid and gaseous fuels and, in some cases, to electricity for cooking. Use of biomass fuels is projected to decline slowly overall, but they will remain the primary source of household energy in much of the developing world for the foreseeable future. According to some estimates, reliance on them may actually have increased recently in some poor areas.

Cooking areas tend to be poorly ventilated in many developing country homes, most of which do not have a separate kitchen. Life revolves around the cooking area and women spend much of their time there. Cooking stoves are mostly simple – often just a pit or three pieces of brick – and burn biofuels inefficiently. Women and young children especially tend to be exposed to high levels of cooking smoke, far exceeding safe levels recommended by the World Health Organization.

This biomass smoke contains many noxious components, including respirable suspended particulates, carbon monoxide, nitrogen oxides, formaldehyde and polyaromatic hydrocarbons such as benzo(a)pyrene. High exposure can damage the respiratory system, eyes and immune system responses – and make people more susceptible to infection and disease. It has been linked to serious health problems, including tuberculosis, acute respiratory infections, chronic obstructive pulmonary disease, cor pulmonale and lung cancer – and associated with asthma, blindness, anaemia and such adverse pregnancy outcomes as low birth weight and perinatal mortality.

Tuberculosis
Recent research suggests that people living in households that rely primarily on biofuels for cooking are two or three times more likely to have active tuberculosis than those in ones that use cleaner fuels. Cooking smoke can increase the risk of tuberculosis by reducing resistance to the initial infection or by promoting the development of active tuberculosis in people who are already infected, or both. Pulmonary tuberculosis, the most common form of the disease, is transmitted by coughing, which is increased by the smoke. Benzo(a)pyrene, a known carcinogen, is found in large quantities in cooking smoke, and there is evidence that this can depress immune system responses.

Acute respiratory infections
These are the single most important cause of morbidity and mortality worldwide, killing more than 3 million children under five every year and accounting for an estimated 9 per cent of the entire global disease burden. Extended exposure to high levels of biomass smoke can impair the clearing ability of the lungs and render them more susceptible to infection. The effects may be particularly severe for young children, who tend to stay indoors and are often carried on their mothers’backs or laps during cooking.

Chronic obstructive pulmonary disease
Repeated or severe childhood chest infections can also lead to chronic lung diseases in adulthood. A number of studies have reported an association between exposure to biomass smoke and chronic bronchitis or obstructive lung disease.

Asthma
Smoke is more likely to aggravate asthma, triggering an attack, than to cause it in the first place. However, repeated attacks due to smoke exposure may leave the person more vulnerable to lower doses and increase the severity of attacks. Exposure to fine particulate matter in smoke has been linked with increased symptoms of asthma and visits to emergency rooms. Evidence of the role of cooking smoke in causing asthma is mixed, but it has some of the same pollutants that are found in ambient air pollution or tobacco smoke, both of which have been linked with the disease.

There will have to be an affordable and sustainable approach which gives high priority to local needs and community participation

Anaemia and adverse pregnancy outcomes
Smoke from burning biomass contains large quantities of carbon monoxide (CO), which can bind with haemoglobin in the blood to make carboxyhaemoglobin (HbCO), effectively reducing the amount of oxygen reaching the body tissues and causing anaemia. This is particularly important for women because they have less haemoglobin in reserve than men, and because their natural levels of HbCO are greatly elevated during pregnancy. Women also do most of the cooking and so are the most exposed to CO. There are no empirical studies linking cooking smoke to anaemia, but there is some evidence that links it to reduced foetal growth, low birth weight and perinatal mortality.

Cataract and blindness
Cataract – the main proximate cause of complete blindness worldwide – is known to be linked to damage to the eye that can be produced by heavy airborne pollution, among other factors. A number of studies in humans indicate that tobacco smoke can cause cataract, suggesting that cooking smoke might have a similar effect, though the research is limited. Trachoma and conjunctivitis, which also cause blindness, could be aggravated by smoke as well.

Lung cancer
Cooking smoke, like tobacco smoke, contains many polycyclic aromatic hydrocarbons, such as benzo(a)pyrene, which can cause cancers. Empirical research has shown an association between exposure to coal smoke and lung cancer, but the evidence linking biomass smoke to lung cancer is limited. Exposure to biomass smoke has also been linked to nasopharyngeal and laryngeal cancers, otitis media (middle ear infection) in children, and cor pulmonale.

There is enough evidence to suggest that cooking smoke has many serious health effects, even though its role in epidemiological transition is not fully understood. By one recent estimate, burning solid household fuels accounts for some 2.5 million premature deaths every year – about 6-7 per cent of the global disease burden, considerably more than that due to ambient urban air pollution.

Overall, some estimates suggest that as much as 25-33 per cent of the global disease burden can be attributed to environmental risk factors. A recent study puts use of unprocessed solid fuels for cooking and heating as the third largest of these, after malnutrition and water/hygiene/sanitation, in causing disability and death in developing countries.

The choice is clear. Millions of lives can be saved and much ill health avoided in developing countries by reducing indoor air pollution levels caused by smoke from cooking and heating. Perhaps the most obvious long-term policy option is to promote a shift from biomass fuels to cleaner ones. Others include promoting better housing and changing behaviour through education programmes about the ill effects of exposure to cooking smoke.