Roughly one billion people worldwide live in slums, settlements defined by inadequate housing, limited access to clean water and sanitation, insecure land tenure, and overcrowding.1International Journal of Disaster Risk Reduction. A global (South) collective burden: A systematic review of the current state of climate-related hazards in informal settlements That number has been climbing for decades, driven by rapid urbanization in regions where governments have not kept pace with housing demand. The word “slum” carries stigma, and many researchers now prefer “informal settlement,” but whatever the label, the phenomenon raises urgent questions about public health, governance, economic opportunity, and what kinds of policy interventions actually help.
Why Slums Form
The single biggest driver is the gap between how fast cities grow and how slowly their governments build infrastructure. When millions of people move to urban areas for work, and the city has neither enough affordable housing nor the planning capacity to create it, people improvise. They build on marginal land, along flood channels, on steep hillsides, next to railroad tracks, or on the periphery of industrial zones. The structures are assembled from whatever is available and affordable.
This is not a failure of the people moving in. Research on slum formation has consistently pointed to a governance problem: city authorities focused on economic growth tend to neglect housing provision, and the result is that self-built settlements become the default solution to a housing shortage the formal sector never addressed.2PubMed Central. Urbanization and slum formation Strategic planning and intervention lag behind the pace of urban growth, and the disconnect between economic development plans and housing needs keeps repeating in city after city across the Global South.
Land markets play a role too. In many cities, formal land registration is slow, expensive, or inaccessible to the poor, which pushes low-income families into areas where tenure is ambiguous. Once a settlement is established, its residents often lack the legal standing to demand services from the city, which reinforces the cycle of underinvestment.
What Living Conditions Look Like
The physical conditions within slums vary enormously, from tightly packed but structurally sound neighborhoods in some Asian cities to fragile shacks with no plumbing in parts of sub-Saharan Africa. But certain problems recur almost everywhere: shared or nonexistent toilets, unreliable water supply, lack of waste collection, and housing materials that cannot withstand storms or floods.
Overcrowding is the feature that most distinguishes slum life from other forms of urban poverty. Families of five or six sharing a single room are common. This density shapes everything else, from how diseases spread to how much noise and stress residents endure daily. And because many slum neighborhoods sit on land nobody else wanted, they are disproportionately exposed to environmental hazards like flooding, landslides, and industrial pollution.
Health Burdens Beyond Infectious Disease
When people think of health problems in slums, they tend to picture waterborne illness or tuberculosis. Those are real concerns, but the health picture is more complicated than the stereotype suggests. Chronic conditions like high blood pressure, diabetes, and obesity are strikingly common, sometimes at rates that rival or exceed those in wealthier urban neighborhoods.
A population-based survey in Rio de Janeiro’s slums found that high blood pressure affected about 30 percent of men and 36 percent of women, while obesity rates reached 19 percent among men and nearly 26 percent among women. About a fifth of men and nearly a third of women had two or more chronic conditions at the same time.3PubMed Central. Prevalence of chronic non-communicable diseases and multimorbidity among adults living in slums in Rio de Janeiro, Brazil: a population-based survey A separate study of urban slum residents found that nearly 90 percent consumed too few fruits and vegetables, over 40 percent used tobacco, and close to 60 percent had three or more major risk factors clustered together.4Journal of Heart Valve Disease. Epidemiological Assessment of Lifestyle Risk Factors Contributing to Non-Communicable Diseases in Urban Slum Populations
Mental health deserves attention here too. A survey across slums in Haiti found that nearly a quarter of adults screened positive for severe psychological distress, making it the single most common health problem reported, ahead of hypertension and physical injury.5PubMed Central. High Burden of Non-communicable Diseases among a Young Slum Population in Haiti Noise, overcrowding, insecure tenure, violence, and the constant stress of poverty all compound. The mental health burden in slums is probably one of the most under-counted problems in global public health.
How Pandemics Hit Slums Harder
The COVID-19 pandemic made the vulnerability of densely packed settlements painfully visible. Analysis of mobile phone data from millions of users in Brazil showed that residents of overcrowded slums simply could not practice social distancing the way other urban residents did after the outbreak began.6Journal of Development Economics. Slums and pandemics If your household has one room and no yard, “stay home and avoid contact” is not a meaningful instruction.
The outcomes matched the exposure. Research examining caseloads across neighborhoods in cities in the developing world found that even after accounting for population density, COVID case rates per capita were consistently higher in slum neighborhoods than in non-slum areas of the same cities. The urban poor bore a disproportionate share of the epidemic’s toll, and density was a critical factor mediating that disparity.7PubMed Central. Spread of COVID-19 in urban neighbourhoods and slums of the developing world This pattern is not unique to COVID. Cholera, dengue, and tuberculosis all follow similar density-driven logic, which means future pandemics will likely reproduce these same inequities unless housing conditions change.
Economic Life Inside Slums
Slums are not just places where people sleep. They are economic ecosystems. Informal businesses, from roadside food stalls to repair shops to small-scale manufacturing, are woven into daily life. The assumption that slum residents are uniformly unemployed or destitute misses the reality that many households are running small enterprises and using the income to keep themselves above the worst levels of poverty.
A study of over 1,700 households in Nairobi’s slums found that household microenterprises were helping offset poverty, particularly for families that were otherwise most likely to be poor. Performance of these businesses depended partly on business-related factors like how long the enterprise had been running and where it could sell goods. But the study also found something important that gets less attention: living conditions themselves influenced whether people could start and sustain a business. Secure tenure and access to basic infrastructure made a measurable difference. Households that were constantly at risk of eviction, or that lacked reliable water and electricity, had a harder time building lasting enterprises.8World Development. Inside Informality: The Links Between Poverty, Microenterprises, and Living Conditions in Nairobi’s Slums
This finding has practical implications. Poverty-reduction programs that focus exclusively on business training or microcredit without also addressing housing insecurity and infrastructure gaps may be tackling only half the problem.
How Slum Communities Govern Themselves
One of the most underappreciated aspects of slum life is that these are not anarchic spaces. They have governance, just not the formal kind. Where city governments are absent or ineffective, residents create their own systems for resolving disputes, managing shared resources, and connecting with external power structures.
Research in Delhi’s slums found that the type of governance depends heavily on the settlement’s ethnic composition and age. Ethnically homogeneous slums tend to transplant rural institutions to the city, relying on leaders who gained authority back in the village. Newer, more diverse settlements depend on informal leaders whose authority comes from political connections, education, and their ability to broker networks. In both cases, informal leaders were accessible to all residents, while formal government figures were most easily accessed by the wealthy and well-connected.9World Development. Governance in the Gullies: Democratic Responsiveness and Leadership in Delhi’s Slums
These informal governance systems have real strengths. A review of governance practices in informal settlements across several contexts identified effective strategies including collaborative decision-making, resource management aligned with local needs, conflict resolution, and monitoring of shared services. But the same review flagged persistent weaknesses: poor accountability, inadequate leadership, lack of political will from outside authorities, and unclear policies that leave informal structures with no legal standing.10Discover Public Health. Addressing the near absence of formal governance in service provision: governance practices thriving in informal settlements The result is a patchwork that works surprisingly well in some places and falls apart in others, often depending on whether external institutions choose to engage with it or ignore it.
Climate Vulnerability and Environmental Risk
Slums sit at the intersection of poverty and environmental exposure in a way that makes climate change a particularly acute threat. Because settlements are often built on flood-prone land, steep slopes, or reclaimed marshland, even moderate weather events can be catastrophic. A heavy rain that causes inconvenience in a middle-class neighborhood can destroy homes and kill people in a slum a few kilometers away.
A systematic review of climate-related hazards in informal settlements found that the combination of inadequate housing, lack of urban services, and insecure land tenure creates a compounding vulnerability where each factor makes the others worse.11International Journal of Disaster Risk Reduction. A global (South) collective burden: A systematic review of the current state of climate-related hazards in informal settlements A household with a tin roof on an exposed hillside that also lacks drainage and has no legal claim to the land has no way to prepare for floods and no recourse after them. Climate adaptation strategies designed for formal neighborhoods, like building codes, insurance, and zoned drainage, simply do not apply.
As extreme weather events become more frequent, the gap between formal and informal neighborhoods in terms of disaster impact is likely to widen. Many cities in the tropics, where slum populations are largest, are also the cities facing the steepest increases in heat waves, flooding, and sea-level rise.
Upgrading Versus Relocation
Governments have tried two broad approaches to slums: improve them in place, or move people somewhere else. The evidence increasingly favors the first option.
A study comparing in-situ upgrading and population relocation found that both reduced the share of land used for housing within the original slum boundary, but through different mechanisms. Upgrading reallocated space toward neighborhood infrastructure like roads and drainage, while relocation simply reduced the number of households. The critical difference was what happened next. Only in-situ upgrading produced lasting improvements in housing quality and the socioeconomic status of residents. Upgrading also generated substantial positive spillovers in nearby neighborhoods, including increased formal housing investment and reduced crime. And it was roughly a third cheaper per household than relocation.12National Bureau of Economic Research. In-situ Upgrading or Population Relocation? Direct Impacts and Spatial Spillovers of Slum Renewal Policies
Relocation projects often fail for a predictable reason: they sever the economic and social ties that make slum life viable. A family moved to a housing block on the city’s outskirts may gain a sturdier roof but lose proximity to the market where they earned a living and the social network that provided childcare, credit, and safety. The result is often that relocated families drift back to informal areas closer to their livelihoods, or that the relocation sites themselves degrade into new slums.
Community Participation Makes or Breaks Projects
Even the better approach, in-situ upgrading, fails when it is done to communities rather than with them. A study of upgrading projects in Kibera, one of Nairobi’s largest slums, found that adaptive management with strong community involvement led to more effective outcomes.13Habitat International. Community-supported slum-upgrading: Innovations from Kibera, Nairobi, Kenya When residents help design the project, they can flag practical issues that outside engineers miss, like which pathways flood first or which structures serve as informal community centers.
Conversely, a study of slum upgrading programs that examined participation levels found that when affected residents and local stakeholders were sidelined, the result was mistrust, misconceptions about the project’s goals, poor design decisions, and mixed outcomes overall.14AFRICA HABITAT REVIEW. Mainstreaming Participatory Approaches in Slum Upgrading Programmes The researchers concluded that robust community engagement is not just a nice add-on but a prerequisite for success, and that upgrading projects need to integrate residents’ livelihood activities and economic needs rather than treating housing as a standalone problem.
The Complicated Effects of Land Titles
Giving slum residents formal ownership of their land sounds like an obvious win. If people have secure tenure, the thinking goes, they will invest in better housing, access credit, and their health outcomes will improve. The reality is messier than that.
A review of evidence from several Latin American countries found that land titling did improve some outcomes. In Buenos Aires, families on titled parcels had better housing quality, higher educational attainment, and lower rates of teenage pregnancy compared to families on untitled land. But the health effects were ambiguous. Children on titled parcels had better short-term nutritional measures, yet their weight-for-height scores actually exceeded international medians, suggesting titling may have increased the likelihood of children becoming overweight. A similar pattern appeared in Lima, Peru, where longer durations of titling were associated not with better child growth but with higher rates of overweight and obesity among young children.15The Lancet Global Health. Beyond land tenure and titling: legal recognition as a pivotal determinant of health in urban informal settlements
In Montevideo, Uruguay, the results were even more complicated. Adults in titling-eligible households reported lower rates of hypertension, diabetes, and asthma, and children were less likely to have been ill recently. But infant mortality was actually higher in titling-eligible households, possibly because families invested more in housing improvements and less in healthcare and education.16The Lancet Global Health. Beyond land tenure and titling: legal recognition as a pivotal determinant of health in urban informal settlements The takeaway is not that land titles are bad, but that they are not the silver bullet they are sometimes sold as. Titling affects health through individual-level pathways like housing investment, and those pathways can lead to unintended trade-offs when families have limited resources and must choose between competing priorities.
Mobile Money and Digital Inclusion
One of the more hopeful developments in slum economies over the past decade has been the spread of mobile phones and digital financial services. In many countries, mobile money platforms have given people in informal settlements access to savings, payments, and small loans without needing a bank account or a physical branch.
Research on digital financial inclusion across African countries has found that mobile penetration and internet access have a significant positive relationship with the informal economy and with poverty reduction. Greater financial inclusion, meaning more people with access to accounts, payment systems, and credit, is associated with a more developed informal sector and measurably reduced poverty.17Journal of Enterprising Communities: People and Places in the Global Economy. Digital financial inclusion, informal economy and poverty reduction in Africa
For slum residents specifically, mobile money solves a set of practical problems that formal banking never addressed. You do not need a permanent address or a government ID to open a mobile money account in many countries. You can receive payments from customers, send remittances to relatives in rural areas, and build a small savings buffer, all from a basic phone. This matters for the microenterprise owners described earlier: if insecure tenure and poor infrastructure make it harder to run a business, at least having reliable access to financial services removes one more barrier. The technology is not transformative on its own, but it works with other incremental improvements to expand what is economically possible in a settlement that the formal city largely ignores.
Why the Word Itself Matters
There is an ongoing debate among researchers, policymakers, and residents about whether to use the word “slum” at all. The term carries connotations of squalor and moral failure that do not capture the complexity of these communities. Many residents object to it. The United Nations and various development agencies have increasingly shifted toward “informal settlement,” which is more descriptive and less loaded.
But the terminological shift creates its own problems. “Informal settlement” is a bureaucratic phrase that can obscure urgency. Some advocates argue that the visceral reaction the word “slum” provokes is precisely what is needed to motivate political action and funding. If a polite euphemism makes it easier for policymakers to deprioritize the problem, the euphemism is doing harm. Others counter that stigmatizing language discourages the very residents it claims to help, making them less likely to engage with government programs and more likely to be treated as problems rather than partners.
There is no clean resolution to this tension. What is clear is that the label applied to a neighborhood affects how outsiders treat it and how insiders perceive their own standing. Research on governance in these communities has shown that external recognition and legitimacy are among the factors that determine whether informal governance structures can function effectively, and being labeled a “slum” does not help with that.