Homelessness

Homelessness is the condition of individuals or families lacking a fixed, regular, and adequate nighttime residence. This state often involves exposure to harsh weather, limited access to sanitation, and heightened vulnerability to health risks, violence, and premature death, distinguishing it from mere poverty or substandard housing.^[1] In high-income countries, official counts suggest at least 2 million cases in OECD nations alone as of 2024.^[2]

Definitions and Scope

Core Definitions and Variations

Homelessness refers to the state of lacking a fixed, regular nighttime residence suitable for human habitation.^[3] Core definitions prioritize literal homelessness. Individuals reside in places not intended for sleeping, such as streets, vehicles, abandoned buildings, or emergency shelters. This distinguishes it from temporary arrangements like doubling up with others.^[4] This focus on immediate shelter deprivation is used in assessments of vulnerability to exposure and health risks, rather than broader socioeconomic instability alone.^[5] In the United States, the federal definition under the McKinney-Vento Homeless Assistance Act, codified in 42 U.S.C. § 11302, classifies a person as homeless if they lack a fixed, regular, and adequate nighttime residence. Their primary nighttime residence may also be a supervised shelter designed for temporary stays or a public or private space not ordinarily used for sleeping, such as cars, parks, or transit stations.^[4] The U.S. Department of Housing and Urban Development (HUD) operationalizes this into categories including:

"Literally homeless": unsheltered or in emergency/transitional housing;
Those fleeing domestic violence or exiting institutions without housing plans. It excludes those in overcrowded but stable dwellings unless eviction is imminent within 14 days.^[6]

Internationally, definitions vary significantly.^[7] The European Typology of Homelessness and Housing Exclusion (ETHOS), developed by the European Federation of National Organisations Working with the Homeless (FEANTSA) in 2005 and revised in 2017, categorizes homelessness across four domains. These include rooflessness such as rough sleeping, houselessness such as shelters or inadequate temporary stays, living in insecure housing such as eviction threats or unauthorized occupation, and inadequate housing such as unfit or hazardous dwellings.^[8] In contrast, many developing countries adopt narrower scopes limited to visible street dwellers or shelter residents. These often exclude rural displacement or informal settlements.^[9] Australia's framework incorporates "secondary homelessness" such as frequent hostel moves. Canada's emphasizes those without alternatives to public spaces.^[10] These variations reflect differing emphases on physical shelter versus habitability and security. Narrower definitions focus on acute physical deprivation. Broader definitions include conditions such as insecure tenure or severe overcrowding.^[11] These distinctions also clarify how homelessness differs from related conditions. While poverty encompasses many who maintain some housing, homelessness specifically denotes the lack of any fixed residence. Housing instability involves residing in a fixed location, albeit with risks such as eviction or overcrowding, whereas homelessness entails the absence of such a residence. In Indigenous contexts, "houselessness" refers to the lack of Western-style housing while retaining cultural identity and connections to ancestral lands through temporary mobility, in contrast to "homelessness," which includes disconnection from lands and community ties beyond physical shelter absence.^[12]^[13]

Measurement and Enumeration Challenges

Enumerating the homeless population presents significant methodological difficulties due to inconsistent definitions (as outlined in Core Definitions and Variations), the transient nature of the affected individuals, and limitations in data collection techniques.^[14] These definitional divergences yield inconsistent data that complicate both national counts and cross-national comparisons, leading to divergent prevalence estimates.^[7] In the United States, the predominant method is the annual Point-in-Time (PIT) count mandated by HUD. This involves a one-night snapshot of sheltered and unsheltered individuals conducted by local Continuums of Care (CoCs).^[15] The approach captures only a single moment, typically in January when weather may drive more individuals indoors. It misses highly mobile or concealed individuals residing in vehicles, abandoned structures, or other non-obvious locations.^[16]^[12] Additional enumeration hurdles include the reluctance of individuals to participate due to distrust of authorities, as well as inconsistencies in volunteer training and data validation across CoCs.^[18] Capture-recapture methods and service-based registries offer alternatives. These methods can produce biases from overlapping counts or exclusion of non-users. Lack of dedicated funding limits rigorous implementation.^[14] Internationally, OECD data reveal wide variations in measured rates, from under 10 per 100,000 in some nations to over 100 in others.^[19] These challenges contribute to undercounts that affect policy evaluation. U.S. federal assessments note that PIT data represent only a fraction of episodic or chronic homelessness episodes occurring over a year.^[12]^[20] Narrow definitions of homelessness undercount "hidden homelessness," such as couch-surfing or doubling up in overcrowded households, which affects additional millions but lacks consistent enumeration due to reliance on self-reporting.^[13]^[22] PIT counts particularly fail to capture this form, as it involves individuals who remain out of public view, often in transient arrangements. This phenomenon disproportionately impacts youth, women, and families, exacerbating undercounts through their reluctance to disclose circumstances and the episodic nature of such experiences. Studies estimate hidden homelessness adds significantly to visible counts, yet methodological challenges like inconsistent self-reporting and mobility hinder precise measurement.^[13]

Historical Development

Pre-Industrial and 19th-Century Patterns

In pre-industrial Europe, particularly England, homelessness manifested primarily as vagrancy. It had roots in 14th-century statutes aimed at controlling itinerant beggars and the able-bodied unemployed amid post-Black Death labor shortages.^[23] These early laws imposed punishments such as whipping or confinement for those wandering without visible means of support.^[24] By the 16th century, the Elizabethan Poor Law of 1601 formalized a parish-based relief system. It categorized the poor into the "impotent" (deserving, such as the elderly, disabled, or orphans, eligible for outdoor relief) and the "idle" or vagrants (undeserving, subject to forced labor or corporal punishment).^[25] This framework, enforced locally through overseers, aimed to minimize public begging while compelling work from the able-bodied. Vagrants faced stocks, branding, or transportation for recidivism.^[26] Laws framed vagrancy as arising from personal refusal to labor.^[27] Records indicate limited large-scale urban homelessness due to predominantly rural populations. Enclosures displaced some peasants into seasonal migration.^[28] Colonial America adopted similar English poor laws by the 17th century, establishing almshouses and vagrancy controls to manage transients in growing settlements.^[26] The Industrial Revolution in the 19th century involved rapid urbanization and economic dislocation. Rural migrants moved to factories in England and the United States. These migrants encountered cyclical unemployment and housing shortages.^[28] In England, the 1834 Poor Law Amendment Act centralized relief into workhouses. Workhouses featured austere conditions, family separation, and mandated labor. The act sought to deter applicants other than the truly needy. Contemporary perspectives linked pauperism to moral failing, amid Malthusian concerns over population growth exceeding wages.^[25] London's streets included rough sleepers. Estimates place homeless children at up to 30,000 by mid-century. Adults used "two-penny hangovers" in rope-supported doss houses or police lodging rooms.^[29] In the United States, industrialization produced comparable patterns. Vagrancy arrests increased in cities including New York and Philadelphia. During 1830s depressions, tens of thousands used municipal lodging houses annually. Districts such as the Bowery housed tramps, with saloons functioning as de facto shelters.^[30] Poorhouses expanded. They accommodated the indigent under regimented labor regimens. Overcrowding and disease prevailed. Market-driven migration occurred alongside rises in visible destitution.^[31] Responses during these periods focused on deterrence and local fiscal restraint, in place of expansive aid. Policies addressed homelessness through individual discipline amid economic expansion.^[28]

20th-Century Shifts and Policy Influences

Deinstitutionalization policies in the United States, formalized by the Community Mental Health Act of 1963, aimed to replace large institutions with community-based care centers. These policies reduced state mental hospital populations from approximately 559,000 in 1955 to 193,000 by 1970.^[28] They released individuals with severe mental illnesses into communities. Funding shortfalls and inadequate infrastructure, however, resulted in insufficient supportive services. This shift coincided with changes in homelessness patterns during the mid-20th century. Former patients faced increased vulnerability to homelessness as a result. By later decades, 25–30% of the homeless population suffered from severe mental disorders.^[32] ^[33] Following exposés of institutional abuses and civil rights concerns, transinstitutionalization occurred into jails, prisons, and streets.^[34] In Europe, 20th-century homelessness policies evolved within welfare frameworks. Post-World War II expansions in social housing and universal benefits initially reduced rates compared to the U.S. Structural shifts toward entrepreneurial urbanism in the late 20th century coincided with decreased affordable accommodations in cities such as London and Paris.^[35] ^[36] Countries such as the UK implemented reforms in the 1980s that included deregulation of housing markets and reduced public spending. These reforms coincided with increases in rough sleeping despite lower baseline rates. England's statutory homelessness acceptances peaked in the early 1980s. Partial recoveries followed through targeted interventions.^[37]

Late 20th to Early 21st-Century Trends

In the United States, the early 1980s economic recession coincided with policy shifts under the Reagan administration. Federal budget cuts reduced HUD funding for housing programs from approximately $29 billion in 1976 to $17 billion by 1990.^[38] Stagnant wages and rising urban rents outpaced affordability for low earners. Lingering effects of deinstitutionalization, as outlined in prior periods, contributed to vulnerability among low-income populations.^[28] The crack cocaine epidemic from the mid-1980s intertwined substance abuse with housing instability.^[28] The HIV/AIDS crisis amplified risks, as affected individuals faced eviction, discrimination, and overwhelmed social services.^[28] These factors marked the onset of what is often termed the modern era of the crisis. Homelessness surged visibly in urban areas during the 1980s, with estimates suggesting hundreds of thousands affected.^[39] By the 1990s, strong economic growth and low unemployment rates below 5% in the late 1990s preceded policy interventions. The 1994 Continuum of Care program under the McKinney-Vento Act expanded shelter capacity and coordinated services.^[40] Point-in-time estimates, such as the 1990 U.S. Census Bureau count of approximately 228,621 homeless individuals (likely an undercount due to methodological limitations), reflected a stabilization or modest peak after the 1980s rise. Family homelessness fluctuated with economic cycles. These developments contributed to a reported decline in overall homelessness through the early 2000s. Chronic homelessness saw targeted reductions via initiatives prioritizing permanent housing placements. However, structural factors persisted as ongoing constraints, including the erosion of single-room occupancy units and manufacturing job losses in inner cities, which disproportionately impacted vulnerable groups.^[30]^[15] The 2008 Great Recession strained housing affordability amid foreclosures and over 8 million job losses. Point-in-time counts from HUD's Annual Homeless Assessment Reports indicated around 630,000 individuals in 2008.^[39] Macroeconomic recessions do not consistently correlate with spikes in homelessness. During the Great Recession from 2007 to 2009, U.S. homelessness rates declined in most metropolitan areas. This decline was associated with families doubling up in shared residences and temporary eviction protections, despite widespread job losses. Economic shocks strain affordability, but adaptive behaviors and policy interventions can mitigate immediate outflows into literal homelessness.^[41]^[42] Substance abuse rates among the homeless population remained high, with studies estimating 38% affected by alcohol dependence and 26% by drug dependence.^[28] Globally, comparable data is sparse, but urban centers in Europe and other developed nations experienced increases associated with deindustrialization and welfare reforms in the 1980s-1990s. Enumeration challenges hinder precise trends; for instance, rough sleeping in England rose in the late [20th century](/page/20th century) before policy-driven declines in the 2000s.^[43]

Causal Factors

Individual-Level Causes

Behavioral Factors

Behavioral patterns rooted in personal decisions contribute to the initiation and prolongation of individual homelessness.^[44] These include persistent avoidance of employment opportunities, non-adherence to treatment regimens, and engagement in criminal activities, particularly affecting those without severe comorbidities. Ongoing choices sustain chronic episodes, including patterns of non-compliance with social norms and avoidance of structured environments. Qualitative accounts from homeless individuals cite self-reported decisions, such as interpersonal conflicts and financial mismanagement leading to eviction or relational breakdowns, as precipitating events.^[45] Refusal of available housing or shelter offers occurs in subsets of the homeless population, linked to preferences for autonomy or aversion to institutional rules; in one urban outreach effort, approximately 40% of 375 shelter offers were declined for reasons including desires for privacy and freedom from regulations.^[46] Chronic unsheltered individuals cycle between streets and temporary housing due to difficulties adapting to housed norms, affecting up to 30% of youth in some samples,^[47] with declined assistance correlating to prolonged exposure to environmental risks. Qualitative and quantitative studies on exit barriers, along with empirical analyses, show that behavioral patterns extend homeless spells beyond demographic predictions.^[48] Behavioral factors, alongside substance abuse and mental illness, rank as predominant individual contributors in persistence analyses, outranking relational factors like domestic violence in predictive models.^[49]

Mental Health and SUD Prevalence

A substantial proportion of individuals experiencing homelessness suffer from mental health disorders and substance use disorders (SUDs), which frequently co-occur.^[50] ^[51] ^[33] Meta-analyses indicate a current prevalence of mental health disorders at 67% (95% CI, 55-77%) and lifetime prevalence at 77% (95% CI, 70-83%).^[52] ^[53] ^[54] Serious mental illnesses (SMI), which include schizophrenia, schizoaffective disorder, bipolar disorder, and severe major depression, affect at least one in five individuals experiencing homelessness,^[54] with approximately 22% of U.S. adults experiencing homelessness reporting SMI in 2024—a rate exceeding that in the housed population.^[55] SUDs affect about 38% with alcohol or drug dependence and 18% according to 2023 analyses,^[56] ^[55] while up to 65% of chronic homeless individuals report lifetime illicit drug use, such as opioids or methamphetamine.^[57] ^[58] ^[59] The fentanyl epidemic has contributed to increased overdose deaths among the homeless in Western cities.^[60] Longitudinal studies indicate that mental health disorders and SUDs often precede the onset of homelessness, with psychopathology and substance abuse antedating housing loss in most cases.^[61] ^[62] These disorders impair cognitive functions, decision-making, and tenancy compliance, elevating entry risks independent of socioeconomic status.^[50] ^[51] ^[33]

Longitudinal Findings

Longitudinal and prospective studies show that psychopathology and substance use disorders (SUDs) often precede or predict housing loss and first-time homelessness.^[61] ^[63] ^[64] ^[65] Symptoms such as delusions, mania, and addiction-driven relapse contribute to evictions, job loss, or resource exhaustion, while these dynamics interact with structural factors.^[66] ^[67]

Systemic and Structural Causes

Systemic and structural causes of homelessness encompass societal-level factors such as housing market constraints, policy decisions, and economic pressures that limit access to stable shelter for vulnerable populations. In rich countries, housing markets and social supports prevent eviction among low-income households until triggers such as job loss or family breakdown occur. Shortages in affordable housing show strong associations with elevated homelessness rates. Regions with high rent burdens relative to incomes exhibit higher rates. A 2023 Pew Charitable Trusts study found strong positive correlations between urban rent prices and per capita homelessness across U.S. metropolitan areas. In that study, a 5% increase in rents associated with up to a 9% rise in homelessness in high-cost cities.^[68] The U.S. Department of Housing and Urban Development's 2024 Annual Homelessness Assessment Report documented a national sheltered and unsheltered homeless population exceeding 650,000 in 2023. The report associated much of the 12% year-over-year increase with gaps in affordable units amid rising costs. Over 17 million extremely low-income households spent more than half their income on rent. Housing shortages exacerbate outflows from institutions into streets.^[69]^[70]

Mental Health Policy

Mental health policy shortcomings, including deinstitutionalization without adequate community supports, have amplified homelessness risks for individuals with severe mental illnesses. Approximately 30% of the homeless population have severe mental illnesses. This rate links to transinstitutionalization into prisons, streets, and jails.^[34]

Housing Policy

Housing policy constraints, including zoning restrictions and regulatory barriers, limit construction, densification, and affordable unit supply, inflating prices, displacing low-income residents, and correlating with higher eviction rates and homelessness—patterns aligning more closely with housing supply elasticity than poverty rates across states and metros.^[71]^[72] A net loss of 2.5 million affordable rental units for extremely low-income U.S. households has occurred since 1980 due to demolitions, conversions to higher-end uses, and insufficient new construction, with regulatory limits suppressing supply in high-demand areas.^[73] National median gross rent reached $1,430 in 2023, exceeding wage growth for bottom-quartile earners.^[74]^[70] Zoning contributes to a 6.8 million unit deficit for low-income renters, with single-family-only zones showing up to 30% higher costs per square foot than flexible areas.^[75]^[76] High rents, vacancy rates below 5%, and eviction surges associate with elevated per capita homelessness, exceeding national averages by 3-5 times in tight markets like California and New York, particularly for single adults.^[77]^[68]^[78] Permissive reforms, such as allowing accessory dwelling units or easing density limits after 2010, yield faster housing growth, lower per capita rates, and unit increases of 0.8% within three to nine years.^[79]

Economic and Housing Market Dynamics

Trends indicate rising global homelessness associated with economic pressures, including inflation, migration, and climate events displacing communities.^[80] Annual forced evictions affect about 15 million people globally, often leading to absolute homelessness.^[81] Income loss from economic conditions such as unemployment and poverty reduces household incomes below thresholds required for stable housing. Low-wage workers face heightened vulnerability when shelter expenditures exceed 30% of income.^[82] Macroeconomic recessions do not consistently correlate with spikes in homelessness. During the Great Recession from 2007 to 2009, U.S. homelessness rates declined in most metropolitan areas. This decline was associated with families doubling up in shared residences and temporary eviction protections, despite widespread job losses.^[41]^[83] Economic shocks strain affordability. Adaptive behaviors and policy interventions can mitigate immediate outflows into literal homelessness.

Familial and Developmental Antecedents

Adverse Childhood Experiences

Childhood experiences of abuse and neglect are associated with elevated risks of homelessness in adulthood. Meta-analyses indicate that adverse childhood experiences (ACEs)—including physical, emotional, and sexual abuse, as well as household dysfunction—confer substantially elevated risks. Individuals reporting four or more ACEs face approximately 16 times the likelihood of experiencing homelessness compared to those with none. Among homeless adults, the prevalence of physical childhood abuse averages 37%, exceeding general population rates of 4-16%. ^[84] Empirical reviews highlight adverse personal histories, such as physical abuse and foster care placement, as precursors to maladaptive coping.^[61] Adverse childhood experiences are linked to disruptions in neurological, immunological, and hormonal development. They are also associated with impairments in the formation of stable social relationships and socioeconomic functioning. These factors correlate with difficulties in maintaining independent housing. ^[84]

Parental Instability

Parental substance abuse and mental illness are linked to family instability, neglect, child removal, and heightened vulnerability to homelessness. Children of parents with substance use disorders encounter heightened housing instability and child welfare involvement. Up to 80% of child welfare cases link to parental substance issues. ^[85] Parental instability and inadequate caregiving during childhood correlate with prolonged homelessness spells in adulthood. Supportive family networks are associated with reduced duration. ^[65]

Foster Care and Out-of-Home Placement

Out-of-home placements, particularly foster care, are associated with acute risks of homelessness, especially among youth aging out. Youth aging out of foster care experience homelessness at rates of 31-46% by age 26. Approximately 25-33% of homeless young adults have foster care histories. ^[86] ^[87] Within foster systems, placement instability (odds ratio 1.163), histories of running away (odds ratio 1.712), and physical abuse (odds ratio 1.438) are linked to increased homelessness risks. These risks often involve unresolved trauma and skill gaps in independent living. ^[86]

Demographics and Regional Variations

Global Overview and Statistics

Estimates of global homelessness vary due to differing definitions, inconsistent data collection, and underreporting. This variation occurs particularly in low- and middle-income countries. Informal settlements and extended family networks obscure counts in these areas. Absolute homelessness involves lacking any form of shelter, such as sleeping rough or in emergency accommodations. It affects approximately 330 million people worldwide as of recent assessments. Inadequate housing includes slums and informal settlements without basic services. Such conditions impact up to 1.6 billion individuals, or about one-fifth of the global population. Despite the prevalence of poverty, the vast majority of individuals living in poverty worldwide reside in housed conditions, with only a small fraction experiencing homelessness. In rich countries, the number of housed individuals in extreme poverty greatly outnumbers those who are literally homeless.^[82] These figures derive from extrapolations by organizations like UN-Habitat and the Institute of Global Homelessness. These organizations highlight challenges in standardizing metrics across regions.^[88]^[89]^[90] Prevalence of absolute homelessness is higher in developing regions such as sub-Saharan Africa and South Asia. These areas account for a disproportionate share of absolute cases. Developed economies report lower absolute numbers. They show higher visibility of chronic homelessness tied to individual factors. OECD countries average 0.25% of the population experiencing homelessness under national definitions.^[2]^[91]^[92] Trends indicate rising homelessness. This occurs alongside economic pressures. As of 2025, 1.12 billion people live in slums. Such trends associate with inflation, migration, and climate events displacing communities. Annual forced evictions affect about 15 million globally. These evictions often lead to absolute homelessness. Official government statistics exist in only 78 countries. These cover a fraction of the global total. Data improvements, such as UN-Habitat's advocacy for standardized reporting, have increased awareness.^[93]^[94]^[95]

Patterns in Developed Nations

Country rates per 100,000 population vary widely, from approximately 6 in Japan to over 200 in the United States and 426 households in England as of 2023, with upticks in Canada and Australia. Across the European Union, homelessness affected over 1.1 million individuals as of 2023.^[19] ^[43] ^[96] Recent trends show rising homelessness in many developed nations, with numbers more than doubling in countries like France and exceeding 400,000 in Germany by 2023, alongside preliminary increases over 40% in some European estimates by 2024.^[43] ^[96]^[97]^[98]^[99]^[100]^[101]^[102] A documented outlier is Finland, where targeted housing programs have halved the rate since the early 2000s, though baseline figures were low and success is attributed to rapid rehousing without preconditions.^[43] Demographic data shows that sheltered homeless populations resemble single, housed poor adults in traits such as low income and education. These populations exhibit heightened vulnerability due to the absence of any residence.^[82] Demographically, homelessness disproportionately impacts men, who comprise over 60% of cases across developed nations. Middle-aged men (35-54 years) dominate at 50-70%. Women represent 20-40%. Unaccompanied youth under 25 account for 10-15%. Foreign-born individuals, particularly from Eastern Europe, Africa, and the Middle East, comprise 25-40% in Western European countries like Germany and France.^[43] ^[89]^[103]^[104] Homelessness concentrates in urban centers, where 70-90% of cases occur, resulting in visible encampments in cities like Los Angeles and London.^[43] Chronic homelessness, defined as over a year unsheltered or multiple episodes, accounts for 20-50% of totals in countries like the US.^[69]

United States Specifics

The January 2024 point-in-time (PIT) count conducted by the Department of Housing and Urban Development (HUD) included 274,224 unsheltered individuals.^[20] Chronic homelessness, defined as long-term or repeated episodes with disabilities, affected about 152,000 people.^[69] Demographically, Black or African American individuals comprised 32% of the homeless population despite being 13% of the general population.^[69] Approximately 7% were veterans, whose numbers declined 7.6% year-over-year due to targeted federal programs like HUD-VASH vouchers.^[105] Unaccompanied youth under 25 numbered around 34,000, while families with children represented 32% of the total.^[69] Regional variations are stark, with California hosting over 187,000 homeless individuals—nearly 24% of the national total.^[106] New York followed with about 91,000, concentrated in urban shelters, while states like Texas and Florida saw increases.^[106] Per capita, Hawaii and Washington, D.C., exceed 50 homeless per 10,000 residents, contrasting with lower rates in the Midwest and South.^[107]

State	Homeless Population (2024 PIT)	Share of National Total
California	187,000	24%
New York	91,000	12%
Florida	25,000	3%
Washington	24,000	3%
Texas	27,000	4%

Patterns in Developing Nations

Homelessness in developing nations commonly involves street sleeping, squatter settlements, or informal slums, particularly among rural-to-urban migrants. These migrants face shortages of affordable housing and employment. Informal slums often represent substandard shelter rather than absolute homelessness. Such patterns differ from individual behavioral patterns more prevalent in wealthier countries.^[108]^[109] Rapid urbanization outpaces infrastructure development, contributing to overcrowded informal housing and vulnerability to eviction. Common manifestations include sprawling informal settlements and migration pressures leading to urban peripheries. Demographic patterns reveal disproportionate impacts on youth and children, women, and migrants from conflict zones. Youth and children comprise up to 30-50% of the homeless in some urban centers, often through urban survival strategies such as street vending. Women are increasingly affected. Migrants from conflict zones experience displacement-related trauma. In contrast to developed contexts, mental health or substance issues appear secondary and often associated with consequences rather than primary causes.^[110]^[108]

Consequences and Associated Risks

Physical Health Outcomes

Homeless individuals experience mortality rates higher than those in the housed population. Non-elderly homeless people in the United States face 3.5 times the mortality risk after adjusting for demographic and geographic factors.^[111] Life expectancy among the homeless averages 42 to 52 years in the United States. This figure is lower than the general population's 78 years. Leading causes of death for those aged 45-64 include heart disease, cancer, drug overdose, and injury.^[112]^[113] This disparity has intensified over time. Homeless mortality increased by 33% from 2010 to 2020 nationwide. This increase is associated with factors including drug overdoses, chronic conditions, and external causes like trauma.^[114] In global contexts, average life expectancy for homeless individuals is around 45–50 years, reflecting documented health risks.^[115] Chronic physical health conditions are more prevalent among the homeless than in the general population. Over 40% of homeless individuals report hypertension. More than 20% report diabetes. Rates of cardiovascular disease reach 18-44% in subgroups with comorbidities like depression or anxiety.^[116]^[117] These conditions are associated with unsheltered living, limited nutrition access, and barriers to consistent medical care. Unsheltered homeless populations show higher burdens of hypertension, diabetes, and cardiovascular disease than sheltered populations. These unsheltered groups also face increased risks of asthma, chronic obstructive pulmonary disease (COPD), and epilepsy.^[118]^[119] Infectious disease rates among the homeless are amplified due to overcrowding in shelters, limited hygiene access, and immune compromise from malnutrition or substance use. The Centers for Disease Control and Prevention identifies heightened vulnerability to tuberculosis (U.S. incidence averaging 36-47 cases per 100,000 from 2006 to 2010, exceeding the national rate of 2.8 per 100,000 by over 10 times), bloodborne infections including hepatitis C (prevalence 3.9-36.2%, exceeding 20% in some cohorts associated with shared needles and unsterile environments) and HIV (0.3-21.1%), and viral hepatitis among homeless populations.^[120]^[121]^[122] SARS-CoV-2 detection reached 1% among asymptomatic individuals in shelters during outbreaks.^[123] Homelessness disrupts preventive care and treatment adherence.^[124] Exposure to extreme weather conditions among unsheltered homeless individuals heightens risks of hypothermia, frostbite, and heat-related illnesses. Studies document substantial morbidity from prolonged outdoor living in inclement conditions.^[125] ^[126] In California, people experiencing homelessness during heat waves from 2012 to 2020 showed increased emergency department visits for dehydration, heat exhaustion, and cardiovascular strain compared to housed individuals.^[126] Injuries from unsafe sleeping sites, assaults, and falls contribute to frequent hospitalizations. Homeless adults face 3 to 5 times higher injury-related emergency visits compared to housed adults.^[127]

Mental Health Outcomes

Homelessness exacerbates existing mental health disorders (see ## Causal Factors). Chronic stressors among the homeless include exposure to violence, sleep deprivation, nutritional deficits, and social isolation.^[33] These stressors contribute to elevated depressive symptoms, as shown in longitudinal analyses of persistent homelessness. Older adults experiencing continued unsheltered living show significantly higher depression scores compared to older adults who secure housing, with mediating factors including frequent victimization and interrupted pharmacotherapy adherence.^[128] Transitions into homelessness are associated with increased episodes of depression and anxiety, while housing instability correlates with heightened rumination and helplessness.^[129] Unsheltered homelessness correlates with higher rates of serious mental illnesses such as schizophrenia and bipolar disorder, including elevated psychosis and functional decline compared to sheltered individuals.^[118] Progression of these conditions is linked to barriers to care, such as stigma and logistical challenges in maintaining appointments or medication regimens. Victimization rates among the homeless are 2-10 times higher than in the general population, correlating with post-traumatic stress disorder (PTSD); untreated trauma further correlates with behavioral disinhibition and repeated housing loss.^[130] Given the mental health deterioration associated with homelessness, interventions providing stable housing correlate with reduced hospitalization rates for psychiatric crises after rehousing. Such interventions are associated with improvements in sleep patterns and cortisol levels. Relapses remain common without addressing comorbid substance use.^[131]

Substance Use Outcomes

Homelessness exacerbates substance use disorders (see ## Causal Factors) through increased exposure to environmental triggers, chronic stress, and barriers to treatment. Unsheltered conditions are associated with higher rates of addiction than sheltered conditions. Studies show that homelessness is associated with continued substance dependence during transitions to adulthood among youth.^[132] Housing instability is associated with reduced adherence to therapies and higher relapse risks. Higher rates of stimulant and opioid misuse relapse have been observed among formerly homeless youth.^[133]^[118]

Victimization and Crime Involvement

Homeless individuals experience disproportionately high rates of victimization compared to the housed population. This includes physical assaults, robberies, and sexual violence. Research cites multiple contributing factors. Studies estimate that 27% to 52% of homeless individuals have been physically or sexually assaulted in the past year.^[134] In a 2024 Los Angeles survey, 16% reported physical violence in the preceding 30 days. Additionally, 7.5% reported sexual violence in the same period.^[135] In San Diego County in 2022, homeless persons were 19 times more likely to be murdered than the housed population. They were 27 times more likely to face attempted murder.^[136] Persistent homelessness is associated with approximately twice the odds of violent victimization, even after controlling for factors like age and health status.^[137] Women experiencing homelessness face elevated threats of sexual assault.^[138] Underreporting of crimes against the homeless is common, stemming from distrust of law enforcement and fear of eviction from encampments.^[139] Most studies find homeless individuals are more often victims than perpetrators.^[130] While homelessness correlates with high victimization, subsets of the population, particularly those with mental illness, exhibit substantially elevated perpetration rates. A 1995 study found violent crime rates 40 times higher and nonviolent crimes 27 times higher among homeless mentally ill individuals relative to domiciled counterparts.^[140] Homeless people are overrepresented among offenders, comprising a disproportionate share of arrests relative to their population size. Offenses are predominantly non-violent public order offenses, such as trespassing, loitering, or petty theft. Nationwide, homeless individuals represent about 4.5% of jail bookings despite comprising roughly 0.2% of the U.S. population.^[141] In the United States, individuals experiencing homelessness are 11 times more likely to be arrested than housed counterparts.^[142] Among state and federal prisoners, 9% reported homelessness in the year prior to arrest.^[143] A survey of incarcerated homeless individuals revealed 93% of their arrests were for non-violent offenses.^[144] In 32 states analyzed in 2025, over 10% of unsheltered homeless adults were registered sex offenders, a rate far exceeding the general population.^[145] Researchers note that poverty and untreated conditions are associated with both vulnerability and offending. Homeless persons hold criminal records at rates exceeding the housed average.^[146] Aggregate data show no evidence that homeless populations are associated with overall violent crime rates; their offenses cluster in property and public order categories.^[147] Studies report higher rates of open drug use, nuisance activities, and property crime near homeless encampments. Areas adjacent to such sites exhibit elevated incidences of petty theft, assault, property damage, and public intoxication. Empirical analyses indicate that encampment removals and closures are associated with reductions in these crimes. A New York City case study documented significant declines in reported theft, assault, and public disorder following closure.^[148]^[149] Broader evaluations observe modest reductions in property and violent crime. These dynamics strain law enforcement resources. Sales prices for properties near shelters in Manhattan were reduced by 17 percent.^[150] Untreated mental health and addiction are associated with visible disturbances such as reported panhandling incidents. Peer-reviewed data highlight disproportionate arrest rates for drug possession and vandalism among the homeless.^[136]

Interventions and Policy Approaches

Supportive Housing Models

Supportive housing models combine permanent, affordable housing with integrated supportive services. These models address chronic homelessness, particularly among individuals with disabilities such as severe mental illness, substance use disorders, or physical impairments. Support includes case management, mental health treatment, vocational training, and medical care. Funding occurs through government subsidies such as Section 8 vouchers or public housing authorities.^[151] Supportive housing differs from transitional or emergency shelters in providing housing in community settings. Services aim to support housing retention without mandating behavioral compliance.^[152] Prominent variants include treatment-first approaches, which condition housing eligibility on sobriety or therapy participation, and Housing First. The Housing First model was pioneered by psychologist Sam Tsemberis in New York City in the early 1990s through the Pathways to Housing program.^[153]^[154] It provides immediate access to permanent, subsidized housing without preconditions such as sobriety, treatment compliance, or income requirements. Optional supportive services follow, tailored to individual needs. Implementation uses scatter-site leasing of private-market apartments. Services adopt a harm-reduction philosophy. This approach permits substance use in housing while encouraging voluntary engagement. The model is commonly used for individuals with severe mental illness or long-term homelessness.^[155]^[156] These models have influenced policies in the United States, Canada, and Europe. In the United States, the Department of Housing and Urban Development's Permanent Supportive Housing (PSH) program, implemented since the 2000s, funded over 300,000 PSH units by 2023 and targeted chronic homelessness defined as one year or more without stable housing plus a disability.^[157] Notable implementations include Utah's 2005 statewide initiative targeting the most chronic cases with multidisciplinary coordination; Canada's At Home/Chez Soi project (2009–2014), which enrolled over 2,000 participants across five cities using assertive community treatment teams; and Finland's 2008 national strategy under PAASO, which converted shelters into permanent units and built thousands of apartments with integrated municipal services.^[158]^[159]^[160]^[161] Adaptations for youth incorporate family reunification and education support in programs in Europe and Canada. Family-oriented models in the U.S. and Canada provide larger units.^[162] Implementation challenges include securing affordable housing stock amid market shortages. Programs require ongoing funding for subsidies and staffing. Leasing often relies on public-private partnerships or government mandates.^[163] Studies evaluating Housing First programs report high rates of initial housing retention. Systematic reviews report an 88% reduction in days spent homeless for Housing First compared to treatment-first models.^[164]^[165] These reviews report 41% higher housing stability for Housing First compared to treatment-first models. Reported annual costs for Housing First range from $14,000 to $50,000 per person, covering subsidized rent and intensive case management.^[166]^[167]

Treatment and Rehabilitation Strategies

Treatment and rehabilitation strategies for individuals experiencing homelessness address co-occurring conditions, particularly substance use disorders (SUDs) and mental illnesses. Empirical data associate SUDs with chronic homelessness in up to 38% of cases involving SUDs alone. Higher rates occur with dual diagnoses.^[168] These approaches integrate behavioral therapies, pharmacotherapy, and case management to support symptom management and substance use management, often within community-based or residential settings.^[169] Addiction and mental health interventions include evidence-based modalities like medication-assisted treatment (MAT) with methadone or buprenorphine for opioid use disorder, contingency management using incentives for abstinence, and cognitive-behavioral therapy (CBT) tailored to street stressors. Randomized trials show modest reductions in substance use severity.^[170]^[171] A 2025 systematic review of psychosocial interventions found moderate effects on curbing problematic alcohol and drug use among homeless adults, with individual formats showing greater effect sizes than group sessions.^[169] Integrated dual-diagnosis treatment combines SUD and psychiatric care, outperforming segregated models in adherence. Concurrent pharmacotherapy accompanies assertive community treatment (ACT) teams, which deliver antipsychotics, mood stabilizers, and psychotherapy in outreach settings. Controlled studies show such approaches reduce hospitalization by 20-30% in chronic cases, prevalent in 20-25% of the homeless population and including conditions like schizophrenia and bipolar disorder. Motivational interviewing, trauma-informed care, and Critical Time Intervention (CTI)—a nine-month transitional program—facilitate service linkages and show reductions in recurrence.^[33] Meta-analyses indicate small to moderate effect sizes for tailored psychological interventions, improving quality of life, depression, and anxiety symptoms. Integrated models like dual-diagnosis clinics achieve retention up to 60% at 6 months.^[171]^[172] Programs may be mandatory or voluntary. Mandatory programs typically involve court-ordered interventions, such as drug courts, or civil commitments under laws permitting involuntary hospitalization or outpatient treatment for severe addiction or serious mental illness (SMI) when individuals pose grave danger to themselves or others.^[173] Voluntary programs rely on self-referral, with incentives like shelter access.^[174] Empirical evidence on outcomes is mixed. Systematic reviews indicate compulsory treatment does not consistently outperform voluntary alternatives in long-term abstinence, drug use reduction, or recidivism. A 2016 review of nine studies (n=10,699) found one-third showed no significant impacts, while others reported short-term benefits, primarily in criminal justice contexts.^[175] A 2012 analysis of U.S. drug court data showed mandated participants achieved higher treatment completion rates and better short-term (one-year) outcomes in re-arrest and drug use reduction compared to voluntary entrants, though long-term (five-year) results converged.^[176] Contrasting evidence suggests voluntary treatment sometimes yields superior long-term abstinence due to higher commitment, with selection bias confounding comparisons.^[177] For high-risk homeless subgroups with chronic addiction or SMI, voluntary retention rates are low, with dropout reaching two-thirds. Washington's Special Commitment Center showed a 15% lower homelessness likelihood post-treatment compared to voluntary detox (29% vs. 34%), with lower emergency use and hospitalizations.^[178] New York's Kendra's Law involuntary outpatient commitment for individuals with SMI and substance comorbidity showed a 64% reduction in homelessness, plus drops in hospitalization and arrests.^[179] A 2021 quasi-experimental study in China found compulsory rehabilitation equivalent to voluntary in employment, income, and family reintegration over two years among 1,200 participants.^[180] Critics highlight risks of trauma, fractured trust, elevated post-release overdose rates, ethical concerns over coercion, high resource demands, and implementation biases like racial disparities.^[181]^[182]^[183] State programs, such as California's 2023 CARE Court, provide examples of involuntary commitment approaches.

Enforcement and Deterrence Measures

In the United States, enforcement measures against homelessness typically involve ordinances prohibiting public camping, sleeping, or panhandling. These ordinances are enforced through fines, citations, or arrests. Measures also include periodic clearances of unauthorized encampments by law enforcement and sanitation teams. The U.S. Supreme Court's 6-3 decision in City of Grants Pass v. Johnson on June 28, 2024, held that such regulations do not constitute cruel and unusual punishment under the Eighth Amendment, even in jurisdictions lacking sufficient shelter beds.^[184] The ruling overturned Ninth Circuit precedents that had restricted enforcement absent adequate housing alternatives.^[185] By early 2025, reports indicate that approximately 150 cities across 32 states had enacted or strengthened bans on outdoor sleeping, with another 40 pending. These bans are often coupled with offers of shelter during operations.^[186] Encampment clearances involve coordinated sweeps to dismantle temporary shelters and remove debris. Officials cite public health risks such as fire hazards or sanitation issues for these clearances. Criminalization policies encompass local ordinances prohibiting behaviors associated with homelessness, such as sleeping or camping in public spaces, panhandling, loitering, and vagrancy. Enforcement occurs through fines or jail time.^[187] Proponents argue that deterrence effects arise from imposing penalties to encourage shelter utilization or behavioral change, addressing concerns over public camping. Empirical findings indicate short-term reductions in visible encampments and localized disorder, alongside some correlations with lower homelessness rates in high-enforcement areas, but outcomes vary by location. High recidivism persists without treatment for underlying factors like substance abuse, often leading to displacement rather than resolution of housing deficits. Enforcement burdens courts with caseloads and incurs operational costs, showing limited standalone impact on overall rates or root causes, though integration with housing or mandates can mitigate recurrence.^[188]

Debates and Empirical Critiques

Effectiveness and Critiques

Debates on homelessness policies, particularly the Housing First model, contrast views on individual-level outcomes with aggregate-level patterns. Proponents highlight its provision of immediate housing without preconditions, which stabilizes subsets of the homeless population and is associated with reduced short-term service utilization. Critics argue that these approaches do not incorporate requirements for addressing behavioral factors such as substance use and mental illness, with studies reporting recidivism rates that remain common and public expenditures that continue or increase without corresponding reductions in overall homelessness rates.^[189]^[190] This analytical divide centers on whether policy success is measured by client-centered retention metrics or by community-wide prevalence declines, with evidence indicating that the former shows modest gains at scale while the latter has not been observed despite expanded funding.^[191]^[192] Analysts also debate the role of treatment mandates, with some positions favoring conditional models that include requirements for addressing root causes, in contrast to Housing First's non-coercive approach, which empirical reviews report as showing minimal or inconsistent effects on addiction or psychiatric symptoms. Critiques of treatment and rehabilitation strategies highlight mixed outcomes on mandatory treatment efficacy, including equivocal or negative impacts on substance use compared to voluntary alternatives, and low retention rates in voluntary programs for high-risk groups with untreated conditions. Systematic reviews indicate that Treatment First models may achieve better engagement in recovery for motivated individuals but yield lower housing stability than Housing First, balancing stability gains against challenges in sustained behavioral change.^[175]^[164] Scalability considerations include per-client costs that often exceed those of traditional shelter alternatives, raising questions about fiscal sustainability in the absence of structural reforms such as zoning deregulation or enforcement of behavioral norms.^[193] Debates further extend to enforcement and deterrence measures, such as encampment clearances and anti-camping ordinances. These approaches demonstrate evidence of reduced public disorder and encampment-related crime in affected areas following implementation, but empirical critiques emphasize their lack of long-term reductions in overall homelessness rates, often resulting in displacement rather than resolution, alongside high enforcement and incarceration costs without addressing underlying individual or systemic causes.^[194]^[195]

Approach	Pros	Cons	Key Evidence
Housing First	Provides immediate housing without preconditions; stabilizes subsets of the homeless; associated with reduced short-term service utilization	Does not address behavioral factors like substance use and mental illness; common recidivism; no reductions in overall homelessness rates; continued or increased public expenditures	Modest client-centered gains but no community-wide prevalence declines despite funding; minimal effects on addiction or psychiatric symptoms^[189]^[190]^[191]^[192]
Mandatory/Conditional Treatment	Favors conditional models addressing root causes	Mixed mandatory treatment efficacy; equivocal or negative impacts on substance use vs. voluntary; lower housing stability than Housing First; high per-client costs	Systematic reviews show challenges in sustained behavioral change and fiscal sustainability^[175]^[164]^[193]
Voluntary Treatment	Better engagement in recovery for motivated individuals	Low retention in voluntary programs	Systematic reviews show challenges in sustained behavioral change and fiscal sustainability^[175]^[164]^[193]
Enforcement and Deterrence Measures	Reduces public disorder and encampment-related crime in affected areas	No long-term reductions in overall homelessness; results in displacement; high enforcement and incarceration costs; does not address underlying causes	Evidence of local improvements but critiques on displacement without resolution^[194]^[195]

Metrics of Success and Measurement Biases

Debates over success metrics highlight differences between output-focused indicators, such as initial housing placements and reduced episode lengths, and outcome-oriented measures like recidivism prevention or aggregate rate reductions. Some analyses argue that system performance metrics, including those from HUD's Continuums of Care, emphasize short-term achievements while giving less weight to returns to homelessness, which can exceed 20-30% and are associated with untreated individual-level issues.^[196] Measurement biases complicate evaluations, as point-in-time counts are subject to methodological variations, seasonal influences, and underenumeration, which may obscure true trends. Positions advocating alternative methods, such as multi-period surveys or administrative data integration, suggest these could yield more robust longitudinal insights, though resource limitations affect their adoption. These debates reflect differing emphases on funding inputs and shelter expansions versus long-term accountability measures.^[69]^[197]^[14]

Competing Explanations

Explanations for chronic homelessness differ in their emphasis between structural and behavioral factors. Structural explanations focus on systemic issues such as housing shortages and economic pressures, suggesting that interventions like expanded supply or subsidies would address the majority of cases. Behavioral explanations emphasize individual factors including untreated substance use disorders and serious mental illnesses as primary drivers, proposing preconditions such as treatment adherence in housing programs. In the United States, these explanations appear in demographic patterns, where Black or African American individuals represent 32% of the homeless population despite comprising 13% of the general population, with interpretations including higher rates of family breakdown, incarceration, and urban poverty concentrations as well as discussions of systemic racism.^[198] Regional variations show states like California with higher per capita homelessness associated with policies limiting enforcement of camping bans and providing robust eviction protections, in contrast to lower rates in the Midwest and South where stricter ordinances, colder weather, and emphases on personal responsibility correlate with fewer encampments.^[199]^[200] These perspectives inform debates over approaches like Housing First, which offers permanent housing without behavioral requirements to address structural barriers. Critics of such models argue that they do not integrate requirements for personal accountability or rehabilitation, potentially sustaining chronic cases, while proponents maintain that they prioritize immediate stability over preconditions that may reduce program uptake.