Indoor Air Pollution

This article was first published in November 2014; last revised in November 2019.

Indoor air pollution is caused by burning solid fuel sources – such as firewood, crop waste, and dung – for cooking and heating.

The burning of such fuels, particularly in poor households, results in air pollution that leads to respiratory diseases which can result in premature death.

Related research entries

Air pollution – in addition to indoor air pollution, outdoor air pollution is also a major global problem. In this entry we provide an overview of the data and research on both forms of air pollution.

Energy access – how does access to electricity and clean cooking fuels compare across the world?

Fossil fuels – how is the production and consumption of fossil fuels changing?

Causes of death – what are people across the world dying from?

Indoor air pollution is one of the leading risk factors for premature death

Indoor air pollution is responsible for 1.6 million premature deaths each year

Indoor air pollution is one of the world’s largest environmental problems – particularly for the poorest in the world who often do not have access to clean fuels for cooking.

The Global Burden of Disease is a major global study on the causes and risk factors for death and disease published in the medical journal The Lancet.1 These estimates of the annual number of deaths attributed to a wide range of risk factors are shown here. This chart is shown for the global total, but can be explored for any country or region using the “change country” toggle.

Indoor air pollution is a risk factor for several of the world’s leading causes of death, including heart disease, pneumonia, stroke, diabetes and lung cancer.2 In the chart we see that it is one of the leading risk factors for death globally.

According to the Global Burden of Disease study 1.6 million people died prematurely in 2017 as a result of indoor air pollution. To put this into context: this was four times the number of homicides – close to 400,000 in 2017.

It’s one of the leading risk factors for deaths globally; but for low-income households, it’s the leading risk factor. If we look at the breakdown for countries with a low sociodemographic index – ‘Low SDI’ on the interactive chart – we see that indoor air pollution tops the list. For low-income countries, the number of premature deaths from air pollution is more than ten times the number from homicides in 2017.3

The global distribution of deaths from indoor air pollution

In low-income countries 6% of all deaths are the result of indoor air pollution

An estimated 1.6 million people died prematurely as a result of indoor air pollution in 2017. This was 3% of global deaths.

In low-income countries, it accounts for 6% of deaths.

In the map here we see the share of annual deaths attributed to indoor air pollution across the world. In 2017 this ranged from a high of close to 11% in Papua New Guinea – more than 1-in-10 deaths – to less than 0.1% across most of Europe and North America.

When we compare the share of deaths attributed to indoor air pollution either over time or between countries, we are not only comparing the extent of indoor air pollution, but its severity in the context of other risk factors for death. Indoor air pollution’s share does not only depend on how many die prematurely from it, but what else people are dying from and how this is changing.

When we look at the share dying from indoor air pollution, figures are high across the lowest-income countries in Sub-Saharan Africa, but not markedly different from countries across Asia or Latin America. There, the severity of indoor air pollution – expressed as the share of deaths – has been masked by the role of other risk factors at low-incomes, such as low access to safe water, poor sanitation and unsafe sex which is a risk factor for HIV/AIDS.

Death rates are highest across low income countries

Death rates from indoor air pollution give us an accurate comparison of differences in its mortality impacts between countries and over time. In contrast to the share of deaths that we studied before, death rates are not influenced by how other causes or risk factors for death are changing.

In this map we see death rates from indoor air pollution across the world. Death rates measure the number of deaths per 100,000 people in a given country or region.

What becomes clear is the large differences in death rates between countries: rates are high in lower-income countries, particularly across Sub-Saharan Africa and Asia. Rates here are often greater than 100 deaths per 100,000 – in Papau New Guinea this was over 200 per 100,000.

Compare this with death rates across high-income countries: across North America rates are below 0.1 deaths per 100,000. That’s a greater than 1000-fold difference.

The issue of indoor air pollution therefore has a clear economic split: it is a problem that has almost been entirely eliminated across high-income countries, but remains a large environmental and health problem at lower incomes.

We see this relationship clearly when we plot death rates versus income, as shown here. There is a strong negative relationship: death rates decline as countries get richer. This is also true when make this comparison between extreme poverty rates and pollution effects.

How has mortality from indoor air pollution changed over time?

Annual deaths from indoor air pollution have declined globally by more than 1 million since 1990

Whilst indoor air pollution is still one of the leading risk factors for mortality, and the largest risk factor at low incomes, the world has also made significant progress in recent decades.

Globally, the number of annual deaths from indoor air pollution has fallen by more than 1 million since 1990. As we see in the visualization, in 1990 an estimated 2.7 million died prematurely as a result; by 2017 this had fallen to 1.6 million.

This means that despite continued population growth in recent decades, the total number of deaths from indoor air pollution has still declined.

Indoor air pollution deaths have declined in most countries

We have seen this progress across a large number of countries. In the scatterplot you see the comparison of the number of deaths from indoor air pollution in 1990 (shown on the y-axis) versus the number in 2017 (on the x-axis). The grey line here marks where the number of deaths would be equal in both years; countries which lie above the line had a higher number of deaths in 1990 than in 2017; and the opposite is true for countries below the line.

Most countries lie above the grey line, meaning most have seen a decline in the number of deaths from indoor air pollution in recent decades.

You can explore data on the number of deaths from indoor air pollution across the world here.

Death rates have declined in almost all countries in the world

Which countries in the world have made progress on tackling indoor air pollution in recent decades? Almost all countries have.

In the scatterplot here we see the comparison between the death rate from indoor air pollution in 1990 (shown on the y-axis) versus the death rate in 2017 (on the x-axis). The grey line here marks where the number of deaths would be equal in both years; countries which lie above the line had a higher number of deaths in 1990 than in 2017; and the opposite is true for countries below the line.

Almost all countries – with the exception of Zimbabwe – lie above the grey line. This means progress has been made almost everywhere in the world in recent decades.

How to make progress against indoor air pollution?

Indoor air pollution results from poor access to clean cooking fuels

Indoor air pollution results from the burning of solid fuels such as crop waste, dung, charcoal and coal for cooking and heating in households. Burning these fuels produces particulate matter – a major health risk, particularly for respiratory diseases. The burning of such fuels in enclosed spaces such as small households is a major risk factor for exacerbation of these diseases.

Low-income households tend to rely on solid fuels for cooking because cleaner fuels are either unavailable or too expensive. We therefore see a strong link between death rates from indoor air pollution and access to clean fuels for cooking.

This is shown in the visualization: here we see that countries with the highest death rate from indoor air pollution are those with very low access to clean fuels (i.e. have a high dependence on solid fuels instead). As access to clean fuels and technologies increases, death rates from household air pollution begin and continue to fall.

Poorer households have a higher dependence on solid fuels

Income is a strong determinant of energy access and types of fuel sources.

In the figure we see the World Health Organization (WHO)’s depiction of the ‘energy ladder’. This energy ladder is shown with income groups along the x-axis (getting richer from left to right) and types of energy sources on the y-axis (transitioning from solid fuels to non-solid fuels).

As shown, very low and low income countries tend to mostly rely on traditional solid fuel sources such as crop waste, dung and firewood. As incomes rise, this energy mix tends to transition towards other solid fuels such as charcoal and coal. It is typically only when households shift within the middle income bracket that fuel sources transition from solid fuels into non-solid fuels (which would be considered cleaner fuels and technologies) such as ethanol, natural gas and finally electricity.

This income-dependent transition is seen in in scatterplot, which shows the percentage of households in any given country with access to clean fuels and technologies for cooking (on the y-axis) versus gross domestic product (GDP) per capita.

The share of households with access to clean energy in countries below a GDP per capita level of $2,000 per year is typically less than 10%. As countries begin to bridge that gap between low and middle incomes, this share begins to increase until a final transition towards high-income where the majority of households have clean fuels and technologies for cooking.

The-energy-ladder---household-energy-and-development-inextricably-linked-– WHO-(2006)
The energy ladder – the link between household energy and development – WHO (2006)4
Access to clean fuels for cooking vs gdp per capita v4 850x600
Click to open interactive version

Access to clean fuels for cooking

Only 60% of the world has access to clean cooking fuels

The obvious way to avoid indoor air pollution from solid fuel burning is for households to transition from traditional ways of cooking and heating towards more modern, cleaner methods. This can, for example, be in the form of transitioning towards non-solid fuels such as natural gas, ethanol or even electric technologies.

The chart shows the percentage of households with access to clean fuels and technologies for cooking.

Globally, access has been increasing: in 2000, 49% of households had access; by 2016 this was 60%. Still, this means access across the world remains low. Less than two-thirds of households have access to clean cooking fuels.

This share has been increasing for most countries at low-to-middle incomes, however, rates of increase vary by country and region.

Access is lowest across Sub-Saharan Africa where only 14% of households in 2016 had access. Progress has been much more significant in South Asia and East Asia over the last decade, with 18 percent and 16% of additional households gaining access, respectively.

Use of solid fuels for cooking is still high, but it is falling

The burning of solid fuels fills the houses and huts in poorer countries with smoke that kills the world’s poor by causing pneumonia, stroke, heart disease, chronic obstructive pulmonary disease, and lung cancer. The solid fuels responsible for this include wood, crop residues, dung, charcoal, and coal. The solution for this problem is straightforward: shift from solid fuels to modern energy sources.

The chart shows that the world is making progress in this direction. In 1980 almost two thirds of the world’s population used solid fuels for their cooking. 30 years later this is down to 41%. The chart also shows that it is a problem associated with poverty: In richer Europe and North America the share is much lower than in the rest of the world; and in the high income countries of the world the use of solid fuels is entirely a thing of the past.

The use of solid fuels is going down in all of the world’s regions. But the success rapidly developing South East Asia is particularly impressive: here the share fell from 95% to 61%.

Methodology

How are deaths caused by pollution estimated?

Indoor air pollution has a wide range of negative health impacts, which can lead to morbidity but also in many cases, mortality. The table features summary data from the World Health Organization (WHO) on the extent of proven links between indoor air pollution and potential health outcomes. These health outcomes range from respiratory infections to chronic obstruction pulmonary disease (COPD) to lung cancer and have varying effects on the population depending on factors such as age and sex.

Health impacts vary in terms of the strength of evidence linking outcomes with indoor air pollution. The WHO define ‘strong evidence’ based on results from a range of studies on solid fuel using in developing countries with biochemical and laboratory evidence of health impacts; ‘moderate I’ has at least three studies showing strong evidence for specific age and sex groups; and ‘moderate II’ has at least three studies showing potential links but with more limited evidence.

Health impacts of indoor air pollution – WHO (2006)5
Health outcome Evidence Population Relative risk Relative risk (95% confidence interval) Sufficient or insufficient evidence?
Acute infections of the lower respiratory tract Strong Children aged 0-4 years 2.3 1.9-2.7 Sufficient
Chronic obstructive pulmonary disease Strong Women aged ≥ 30 years 3.2 2.3-4.8 Sufficient
Moderate I Men aged ≥ 30 years 1.8 1.0-3.2 Sufficient
Lung cancer (coal) Strong Women aged ≥ 30 years 1.9 1.1-3.5 Sufficient
Moderate I Men aged ≥ 30 years 1.5 1.0-2.5 Sufficient
Lung cancer (biomass) Moderate II Women aged ≥ 30 years 1.5 1.0-2.1 Insufficient
Asthma Moderate II Children aged 5-14 years 1.6 1.0-2.5 Insufficient
Moderate II Adults aged ≥ 15 years 1.2 1.0-1.5 Insufficient
Cataracts Moderate II Adults aged ≥ 15 years 1.3 1.0-1.7 Insufficient
Tuberculosis Moderate II Adults aged ≥ 15 years 1.5 1.0-2.4 Insufficient

Data Sources

Institute of Health Metrics and Evaluation (IHME) Global Burden of Disease (GBDx) Data Tool

World Health Organization, Global Health Observatory (GHO)

World Health Organization (WHO)

Food and Agricultural Organization (FAO)
  • Data: Forestry data on wood fuel for countries and world regions since 1961.
  • Geographical coverage: Global- by country
  • Time span: 1990 onwards
  • Available at: http://www.fao.org/faostat/en/#data/FO