Household Air Pollution (HAP) is a major type of indoor air pollution (IAP) that mainly happens because of cooking and heating methods in developing countries. In many areas, cooking is done using fuels like wood, charcoal, animal waste, and plant materials. These fuels are often burned indoors without proper ventilation, which puts millions of people—especially women and children—at risk for serious health problems. About three billion people in developing countries are affected by this issue. The World Health Organization (WHO) says that pollution from cooking causes about 3.8 million deaths each year. A study called the Global Burden of Disease estimated that 3.1 million deaths happened in 2021 because of this problem. This issue is connected to energy poverty and cooking methods.
Smoke from burning solid fuels in homes often includes harmful byproducts, such as fine and coarse particles (like PM2.5 and PM10), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and many other harmful chemicals.
Solutions to this problem often focus on providing better cookstoves. However, changing how people cook and use fuel can also be important.
Problem description and scale
Three billion people in developing countries use biomass fuel, such as wood, charcoal, dung, and crop residue, for cooking and heating. Much of this cooking happens indoors in rooms without good airflow, which causes millions of people, especially women and children, to breathe in harmful tiny particles. The main causes of indoor air pollution are burning fuels and materials used in buildings. In 2012, 4.3 million deaths worldwide were linked to exposure to indoor air pollution, mostly in low- and middle-income countries. Southeast Asia and the Western Pacific regions had the highest number of deaths, with 1.69 million and 1.62 million, respectively. About 600,000 deaths occurred in Africa, 200,000 in the Eastern Mediterranean region, 99,000 in Europe, 81,000 in the Americas, and 19,000 in high-income countries.
Although fewer people are using biomass fuel now, this limited resource may not keep up with population growth, which could harm the environment more.
Over many years, scientists have studied the air pollution caused by burning solid fuels like wood and coal for cooking, heating, and lighting in developing countries. It is now clear that burning solid fuels in inefficient stoves that do not vent smoke properly leads to higher levels of harmful pollutants indoors. This happens because the stoves burn fuel inefficiently, and the smoke is released directly into living spaces. Smoke from burning solid fuels often contains harmful substances, including tiny and larger particles (like PM2.5 and PM10), carbon monoxide, nitrogen dioxide, sulfur dioxide, and other harmful chemicals (such as formaldehyde, benzene, and acrolein). In a typical stove, about 6–20% of the fuel becomes toxic emissions. The exact amount and type of emissions depend on factors like the type of fuel, the stove design, and how the stove is used.
Indoor gas stoves have been connected to health problems, such as an increase in childhood asthma.
Health impacts
Most studies have focused on measuring the levels of particulate matter (PM) and carbon monoxide (CO) in the air that people breathe. These substances are created when fuels burn incompletely and are considered the most harmful to health. About 11% of lung cancer deaths in adults are linked to exposure to cancer-causing substances from household air pollution caused by burning fuels like kerosene, wood, charcoal, or coal for cooking and heating. Indoor PM 2.5 levels, which are tiny particles in the air, have been reported to range from hundreds to thousands of micrograms per cubic meter (μg/m³). Similarly, CO levels have been measured as high as hundreds to over 1,000 milligrams per cubic meter (mg/m³). A recent study of 163 homes in two rural Chinese counties found average indoor PM 2.5 levels of 276 μg/m³ (using a mix of fuels like wood, tobacco stems, and corncobs), 327 μg/m³ (using wood), 144 μg/m³ (using smoky coal), and 96 μg/m³ (using smokeless coal). These results varied based on the type of fuel and stove used, such as vented or unvented stoves, fire pits, or mixed-ventilation stoves.
In rural Kenya, research has been conducted to understand how much pollution is created by burning biomass fuels like wood, animal dung, and crop waste. Smoke from burning solid fuels is inhaled by women and children for up to seven hours daily in enclosed spaces. Pollution levels change based on the time of day, season, and airflow in homes. In homes with poor conditions, pollution levels can be up to 100 times higher than safety standards. Many Kenyan women use a three-stone fire, which produces tiny soot particles that can block and irritate airways in the lungs. Smoke also contains harmful gases like aldehydes, benzene, and carbon monoxide. Exposure to indoor air pollution from burning solid fuels has been linked to several diseases, including acute lower respiratory infections (ALRI), chronic obstructive pulmonary disease (COPD), cataracts, blindness, lung cancer, tuberculosis, premature births, and low birth weight.
As of 2023, over 2.3 billion people in developing countries rely on burning polluting fuels like wood, dried dung, coal, or kerosene for cooking. This practice causes harmful household air pollution and contributes to outdoor air pollution. The World Health Organization (WHO) estimates that cooking-related pollution causes 3.8 million deaths each year. A 2021 study found that 3.1 million deaths were linked to this pollution, with the highest rates in Africa. Household air pollution from burning fuels is connected to many health problems, including increased risks of stroke, pneumonia, and chronic respiratory diseases like COPD. Exposure during pregnancy is also linked to poor birth outcomes, such as low birth weight.
In traditional cooking setups, smoke is often released inside homes instead of being vented outside through a chimney. Smoke from solid fuels contains thousands of substances, many of which are harmful. These include carbon monoxide (CO), tiny particles, nitrous oxide, sulfur oxides, volatile organic compounds like formaldehyde, benzene, and 1,3-butadiene, and polycyclic aromatic compounds like benzo-a-pyrene. These substances may cause both short- and long-term health issues.
Exposure to household air pollution nearly doubles the risk of childhood pneumonia and causes 45% of all pneumonia deaths in children under five. New studies suggest that household air pollution may also increase the risk of cataracts, the leading cause of blindness in lower-middle-income countries, and low birth weight. Cooking with open fires or unsafe stoves is a major cause of burns among women and children in developing countries.
In most households, especially in rural areas and refugee camps, women and girls are primarily responsible for gathering fuel wood for cooking. They also make up the majority of deaths caused by household air pollution. In Nigeria, replacing traditional kerosene or firewood stoves with cleaner ethanol stoves has reduced harmful effects of household air pollution on pregnancies. Anemia, a condition where a woman’s hemoglobin levels drop significantly, and exposure to carbon monoxide (CO) often occur together. Pregnant women with anemia may be more affected by CO pollution than those without anemia.
Approaches
Finding a low-cost solution to reduce the many problems caused by indoor air pollution (IAP) is difficult and requires ongoing work. These problems include improving how fires burn, reducing smoke exposure, increasing safety, lowering the amount of labor needed, saving fuel costs, and ensuring long-term sustainability. In the past, efforts to improve cook stoves, starting in the 1950s, focused mainly on reducing tree cutting but did not address IAP. The success of these early efforts in saving firewood is unclear. Different stove designs had different results. For example, some improved stoves in Kenya reduced smoke particles but increased carbon dioxide and sulfur dioxide emissions. Smoke removal systems, such as flues, were hard to design and often broke easily.
Today, better solutions include smoke hoods, which work like flues but are more effective at reducing IAP than relying only on windows for ventilation. New stoves often have features like chimneys to trap heat, enclosed fire areas, pot holders to improve heat transfer, dampers to control airflow, ceramic inserts to reduce heat loss, and systems to cook multiple dishes at once.
Improving cook stoves is now considered one of the most cost-effective ways to reduce health risks from IAP and, in some areas, ease pressure on the environment from cutting trees for fuel. Large-scale burning of biomass, such as wood, can only be done if it is managed in a way that allows forests and trees to regrow. In Kenya, sustainable solutions might include growing energy crops like trees and shrubs, which could also provide income for farmers. These crops could help protect soil in areas at risk of erosion or flooding because their roots and leaves improve soil strength. Choosing plants that grow naturally without needing tilling or planting is the most sustainable approach. Some people worry this could harm forests, but proper forest management could make this a workable solution.
Cooking fuels and stoves can be evaluated based on two factors: how efficiently they use energy and how much pollution they produce. Stoves that use energy well can help the environment even when using fuels like firewood or biomass. A study comparing different cooking fuels and stoves found that more efficient stoves convert more of the fuel’s energy into useful cooking heat, meaning less fuel needs to be made, transported, and burned for the same amount of cooking.
Other sustainable options include using liquid or gas fuels in efficient stoves. For example, ethanol made from non-food materials like wood or agricultural waste has lower environmental effects than ethanol made from sugar or starch. LPG, which comes from non-renewable fossil fuels, still causes fewer health problems than traditional fuels. While LPG is not a long-term sustainable solution, it produces far less pollution than traditional fuels.
Challenges
There are trade-offs between efficiency and sustainability when making cook stoves and fuels. While creating stoves that use clean and efficient fuel is good for the environment, this is often not possible because of problems with making and using these fuels on a large scale. For example, electric stoves are considered clean because they do not produce pollution at home. However, problems still exist. Power plants that make electricity in countries like India and China often use coal, which harms the environment. Also, only homes connected to the electric grid can use electricity, leaving many people in rural areas without access.
On the demand side, it is hard to encourage people to buy improved cook stoves. Programs must use methods that respect local culture to help people change their habits. Another challenge is the high cost of better stoves. People with very low incomes often cannot afford these stoves because they lack assets or access to loans. New business models and more microfinance programs (small loan services) are helping, but these programs still struggle to grow.
Unclean cook stoves cause harm, including health risks for women and children, environmental damage, and disease from household air pollution (HAP). Because of this, governments should take action. One way is to provide direct financial help linked to health and climate goals, such as subsidies tied to carbon markets. Offering public services like education about cook stoves and access to loans can also help. Supporting research into cleaner technologies and setting basic rules for testing stove efficiency and cleanliness is important for creating a reliable supply chain.
Many groups, including the World Health Organization (WHO), are working to address HAP. In 2023, WHO officials, including Dr. Abdurrahman Diallo, called for government action, especially in Kenya. The focus is on reducing household air pollution and promoting clean energy. WHO says more government action is needed to reduce harmful pollution. Evidence shows that HAP causes serious health problems, so clear policies are needed to improve air quality.
In Nairobi, Kenya, many people live in slums with poor housing and little access to services. These homes often use wood or fossil fuels, and pollution from these fuels enters homes through windows, walls, and ceilings. Local leaders, policymakers, and community members are working together to solve this problem through workshops and field trips.
Even without a complete plan, governments are taking steps to reduce HAP. Donor countries, WHO, and the Global Alliance for Clean Cookstoves (GACC) are pushing for cleaner energy solutions. Strategies include increasing access to clean stoves and improving living conditions to support these changes. Programs that track household energy use, health, and air quality can help hold governments accountable for their policies. WHO has collected data on HAP, which is available in their Global Household Air Pollution Measurement Databases.
In May 2011, a workshop called "Health Burden of Indoor Air Pollution on Women and Children in Developing Countries" brought together over 150 people to study the effects of air pollution. Organized by the National Institutes of Health, the event identified key research areas that could help reduce HAP.
Developments for improved cookstoves
There have been important improvements in energy-efficient cooking methods, such as improved cookstoves. One example is the Wonderbag, which helps reduce the amount of fuel needed for cooking at home. Better technology has made it possible to use more eco-friendly cooking methods with traditional fuels, like the BioLite Home Stove. This stove uses biomass fuel and cuts fuel use by half while reducing harmful emissions by up to 95%.
New business ideas have helped cookstove companies improve costs for both makers and users, while also helping health and the environment. For example, Inyeneri is a company in Rwanda that works like a cooking fuel utility. Its model solves problems like high initial stove costs, people mixing old and new cooking methods, and the difficulty of making these businesses profitable.
Mobile technology has also helped companies like PayGo Energy in Kenya and KopaGas in Tanzania. These companies help low-income people by reducing the high upfront cost of stoves and making it easier to buy small amounts of fuel. Microfinance institutions have also started supporting clean energy access, as seen in the USAID-funded Renewable Energy Microfinance and Microenterprise Program (REMMP).
More national and international efforts are needed to help millions of people who suffer from poverty and illness caused by indoor air pollution. Scientists predict that Africa will be the first region to feel the effects of global warming, putting millions at greater risk because of limited ability to adapt. The potential for a more sustainable Africa is strong if people inside and outside the region work together. Pneumonia is the leading cause of death for children worldwide, and indoor air pollution is a major risk factor for severe pneumonia. The global health community set November 2 as World Pneumonia Day to raise awareness about the disease and its causes.
Improved cookstoves are a positive step, but they are not used enough to achieve their full benefits. These programs are seen as short-term solutions to reduce indoor air pollution. Officials use sensors to track how often these stoves are used, but the data shows that people often use them for only about two months. Some studies found a few users who used them for at least six months. Because of climate change and the effects of air pollution, there is a growing need for long-term studies. Short-term monitoring is not reliable and does not provide enough information to fully understand how effective these stoves are.
Education and behavior change techniques
Educational programs can help reduce smoke exposure by teaching people about the dangers of harmful smoke and encouraging them to change habits and traditions that increase exposure. Changing behavior is one way to influence people's choices, and this can be done through social marketing campaigns. These campaigns usually fall into two categories: large-scale efforts that reach many people, or smaller efforts that focus on local communities and homes, using demonstrations and follow-up visits. Research shows that large-scale campaigns increase awareness of the risks of household air pollution, but they often do not lead to more people buying improved stoves.
When designing these programs, it is important to understand that people’s choices are influenced by many factors, including cultural beliefs, gender roles, how food is prepared, and religious traditions. These factors go beyond just technology or money. A successful example is a government program in China between 1980 and 1995, which distributed 172 million improved cookstoves. This program was more effective because it included local people, especially women, in the planning and hands-on work in the community.
Primary intervention for children
Children under five years old spend most of their time at home. Around the world, half of all pneumonia deaths in children under five are linked to breathing in tiny particles from indoor air pollution. Many homes use solid fuels, like wood or coal, for cooking. These fuels release harmful gases and tiny particles into the air. Breathing in these harmful substances can lead to serious health problems, such as lung cancer or infections in the lungs. Using cleaner fuels like kerosene, gas, or electricity for cooking reduces indoor air pollution. Children in homes that use cleaner fuels have much lower rates of asthma (8.3%) compared to those in homes that burn biomass (46.6-48.8%). To help prevent health issues caused by indoor air pollution, ongoing efforts to reduce exposure to harmful air are essential.
Country examples
In 2004, Kenya showed a willingness to address issues related to biomass energy. The country understood that using biomass for energy can cause indoor air pollution and harm the environment. The United Nations Development Programme suggested creating a special organization to focus on biomass energy. This organization would develop rules for using firewood, charcoal, and modern energy sources like cleaner fuels, wind, solar, and small hydropower. Short-term solutions include using more efficient cook stoves, which are more affordable than switching completely to non-solid fuels. Long-term solutions involve moving to cleaner fuels and renewable energy, supported by international and national policies. Government support for these solutions is possible, as seen in Zambia’s efforts to promote biofuels.
Kenya leads the world in the number of solar power systems installed per person. Each year, over 30,000 small solar panels, producing 12 to 30 watts each, are sold in Kenya. For about $100, a solar panel and wiring can be used to charge a car battery, which can power a light or small TV for a few hours daily. More Kenyans use solar power than connect to the country’s electrical grid.
The Kenya Smoke and Health Project (1998–2001) involved 50 rural households in Kajiado and West Kenya. These areas were chosen because of differences in climate, geography, and culture. The project focused on involving the community, and participants reported better results than expected. Local women’s groups and men in West Kenya were actively involved. Involving end-users led to greater acceptance and created local jobs.
Three main changes were tested: enlarging windows or opening eaves to improve ventilation, adding smoke hoods over cooking areas, or using improved cook stoves like the Upesi stove. Smoke hoods, made from paper and later metal, helped remove smoke from homes. The Upesi stove, made of clay, uses wood and agricultural waste. It cuts fuel use by half, reduces smoke exposure, and provides income for women who make and sell the stoves.
Benefits included better health, with fewer headaches, fatigue, and eye irritation. Smoke hoods kept children and animals safe from fires and reduced soot. Improved lighting allowed women to do beadwork indoors and helped children study. Relationships among women improved, and men supported their wives’ efforts when benefits were shared.
Improved stoves have also helped in other countries. In Guatemala, a study found that improved stoves reduced health risks for mothers and children. In India, a program offering subsidies for improved stoves with chimneys showed lower cataract rates in women. In China, hundreds of millions of improved stoves were installed, improving indoor air quality. However, China’s government has not shared enough data about air pollution effects. With more public awareness through media and the internet, people in China are now more focused on reducing air pollution.