The main cause of homelessness is a lack of affordable housing. While personal crises like job loss, mental illness, and addiction often push individuals onto the streets, large-scale research consistently shows that housing market conditions predict homelessness rates more reliably than any other factor. In 2024, the U.S. recorded 771,480 people experiencing homelessness on a single night, an 18 percent increase from the previous year and the highest count ever documented.
That doesn’t mean personal struggles are irrelevant. Homelessness results from structural pressures and individual vulnerabilities colliding. But understanding which factor carries the most weight matters, because it shapes what solutions actually work.
Housing Costs Are the Strongest Predictor
A major HUD-funded analysis found that housing market factors predicted rates of homelessness more consistently than any other economic variable, including poverty and unemployment. High median rents, overcrowding, and eviction rates were especially strong predictors in urban areas and tight, high-cost markets. Cities with the lowest rental vacancy rates tend to have the highest homelessness rates, because fewer empty units mean less supply relative to demand, which drives prices up.
There’s a specific tipping point. Research by Glynn, Byrne, and Culhane found that homelessness in a community sharply increases once median rental costs exceed 32 percent of median income. That threshold sits right at the federal definition of “cost-burdened” housing, where renters spend more than 30 percent of their income on rent. Communities with a high share of cost-burdened renters see correspondingly higher rates of homelessness, particularly in rural areas and expensive rental markets.
This explains a pattern that confuses many people: why homelessness concentrates in wealthy cities rather than the poorest ones. Higher poverty rates are actually associated with lower homelessness in rural areas, likely because housing there remains cheap enough that even very low incomes can cover rent. It’s the gap between what housing costs and what people earn that matters, not poverty alone.
Mental Illness and Substance Use Disorders
About 22 percent of adults experiencing homelessness on a given night meet the criteria for serious mental illness, roughly four times the rate in the general population. A similar share, 18 percent, have a chronic substance use disorder, compared to about 3 percent of adults overall. These conditions make it harder to maintain steady employment, keep up with rent, and navigate bureaucratic systems for assistance.
The relationship runs in both directions. Mental illness and addiction can lead to housing loss, but homelessness itself worsens both conditions. Living on the street or cycling through shelters creates chronic stress, disrupts treatment, and increases exposure to substances. Once someone is homeless, untreated mental health or addiction problems make it significantly harder to regain stable housing, creating a cycle that’s difficult to break without targeted support.
Incarceration and Institutional Discharge
More than 50,000 people released from jail or prison every year have nowhere to go but the streets or a shelter. People who have been incarcerated are up to 13 times more likely to experience homelessness than the general population. A criminal record makes it harder to pass rental background checks, qualify for public housing, or find a job that pays enough to cover a security deposit and first month’s rent.
The problem extends beyond prisons. People discharged from psychiatric hospitals, substance use treatment facilities, and foster care all face elevated risks of homelessness when there’s no stable housing waiting for them on the other side.
Domestic Violence
Among cities surveyed, 44 percent identified domestic violence as a primary cause of homelessness. For many women and children, leaving an abusive household means choosing between physical safety and having a roof. When someone flees without savings, a co-signed lease, or family nearby, the transition from a dangerous home to no home can happen overnight. Shelter systems for domestic violence survivors are chronically underfunded, and waitlists in many cities stretch for weeks or months.
Medical Debt as a Tipping Point
A sudden health crisis can be the final push into homelessness, especially for people already living on tight margins. A University of Washington study of people experiencing homelessness in King County found that unpaid medical bills were their primary source of debt. More than 80 percent of participants carried some form of debt, and 68 percent of those with debt specifically owed medical bills, the majority of which had been sent to collections.
The financial damage extends the period of homelessness itself. Participants whose medical bills had gone to collections experienced homelessness for an average of 22 months longer than those without medical debt. Collections accounts destroy credit scores, which landlords use to screen applicants. Even when someone is ready to re-enter the housing market, medical debt can lock them out.
Rising Homelessness Among Older Adults
About 146,000 older adults experienced homelessness in 2024, a 6 percent increase from the prior year. This group faces compounding challenges: fixed incomes from Social Security that haven’t kept pace with rising rents, higher rates of chronic health conditions, and mobility limitations that make shelters physically inaccessible. Many shelters rely on bunk beds and shared facilities that older adults with functional impairments simply can’t use. Some need assistance with daily activities like eating or using the bathroom, needs that most emergency shelters aren’t designed to meet.
The aging of the homeless population reflects a broader demographic shift. Many of today’s older homeless adults entered the housing market decades ago when rents were manageable, then watched costs outpace their earnings over time. A single financial shock, whether a medical bill, a landlord selling a property, or the death of a spouse who shared expenses, can tip someone from barely housed to homeless.
Why the Structural Explanation Matters
Personal risk factors like addiction, mental illness, and criminal records exist everywhere, in every city and every income bracket. What differs across communities is housing cost. Cities with affordable, available rental housing absorb personal crises better: someone who loses a job or enters treatment can find a cheap apartment while they recover. In tight, expensive markets, that cushion doesn’t exist, and the same personal crisis leads to the street.
This is why researchers consistently point to housing affordability as the main driver. It’s the variable that explains why homelessness rates differ so dramatically between otherwise similar cities. Personal vulnerabilities determine who becomes homeless within a given community, but housing market conditions determine how many people become homeless overall.