Expert Commentary

Solitary confinement in US prisons: A research-based primer

Estimates from academic and other sources suggest that on any given day there are tens of thousands of prisoners held in solitary confinement in the U.S. We explore the history and costs of the practice.

solitary confinement
(Caitlin Regan / Flickr / Creative Commons)

Solitary confinement is the practice of keeping a prisoner alone in a cell about the size of a parking space, with minimal human contact and limited access to the outdoors.

Corrections officers and officials remove prisoners from the general prison population and place them in solitary confinement for a variety of reasons.

While there is no centralized, current census on the prevalence of solitary confinement, estimates from academic and other sources suggest that on any given day there are tens of thousands of prisoners held in solitary confinement in the U.S.

If you are a journalist who wants to do more reporting on solitary confinement or prison systems generally, you will want to read this primer, which is based on recent and historical research on solitary confinement.

This primer will cover:

  • What solitary confinement is and why is it used.
  • Recent estimates of the prevalence of solitary confinement, and which demographic groups are more likely to be held in solitary.
  • The mental and physical costs of solitary confinement.
  • A brief history of the practice.
  • The economic costs of solitary confinement.
  • Alternatives to solitary confinement.

Keep reading for important background to ground your reporting on this topic.

What is solitary confinement and why is it used?

Solitary prisoners are typically confined to their small cells for 23 hours a day except for an hour in a rec pen, “an outdoor cage connected to a cell by a door,” writes Matthew Azzano in a 2022 article for The Marshall Project. Federal appeals courts have largely held that prisoners in solitary are entitled to outdoor time.

Furniture is usually minimal — an open toilet, a ledge jutting from the wall with a thin foam mattress for a bed. A solitary cell might also have two cement cubes attached to the wall, “forming an awkward chair and desk of sorts,” writes University of California, Irvine criminologist Keramet Reiter in her 2018 book, “23/7: Pelican Bay Prison and the Rise of Long-Term Solitary Confinement.” Some facilities keep the lights on all day and night in their solitary confinement units.

The practice of holding a prisoner in solitary confinement falls under what is called restrictive housing, which the National Institute of Corrections — an agency of the Federal Bureau of Prisonsdefines as “housing some inmates separately from the general population of a correctional institution and imposing restrictions on their movement, behavior, and privileges.”

Prison officials rarely use the term “solitary confinement.” This term is more prevalent among journalists and academic researchers. Prison officials tend to favor the term “segregation” — meaning a prisoner is kept away from the general population for days, weeks or years.

A March 2016 report from the National Institute of Justice, which is the research, development and evaluation agency of the U.S. Department of Justice, describes three situations in which prisoners are typically segregated from the general population:

  • Protective custody is when a prisoner is at risk of being injured by other prisoners.
  • Disciplinary segregation is when a prisoner breaks prison rules and is punished following a hearing.
  • Administrative segregation is when a prisoner poses a threat to members of the general prison population.

“Isolation through solitary confinement is prevalent across both administrative and disciplinary segregation,” according to the report.

But prison officials sometimes send prisoners to solitary for other reasons, including in retaliation for speaking up following assaults allegedly committed by guards, according to recent reporting from Alysia Santo and Joseph Neff at The Marshall Project.

Solitary confinement use by the numbers

Two recent analyses indicate the share of U.S. prisoners held in solitary confinement falls somewhere in the range of 3% to 6%.

A national survey of U.S. prison systems conducted by the Arthur Liman Center for Public Interest Law at Yale Law School estimates there were 41,000 to 48,000 people in restrictive housing as of July 2021.

Thirty-four state prison systems plus the Federal Bureau of Prisons responded to the survey, covering about 61% of the roughly 1.2 million people held in U.S. prisons. Across these jurisdictions, a median of about 3% of people were held in restrictive housing. Ten jurisdictions reported leaving the lights on all night in their solitary confinement units.

The survey defines “restrictive housing” as a prisoner being held in an isolation cell for more than 15 days and for 22 hours per day on average. This is the same as the United Nations’ definition of prolonged solitary confinement in its rules on the treatment of prisoners, known as the Nelson Mandela Rules. These rules, adopted by resolution of the General Assembly in December 2015, are not binding — meaning it is up to each country whether and how to implement them.

The Liman Center has conducted the survey every two years since 2013. The survey data are the only ongoing, current nationals estimates on the use of restrictive housing.

In 2015, the center estimated the were 80,000 to 100,000 prisoners held in restrictive housing. The 2017 survey report estimated 61,000 prisoners held in restrictive housing; the estimate was roughly the same for the 2019 survey report. This reduction of roughly half since 2015 is notable, but there are caveats.

For example, the authors of the 2021 Liman survey report write that “a jurisdiction that held people in isolation for no more than twenty-one hours per day would appear in the Survey data as holding no people in restrictive housing.”

During the early part of the COVID-19 pandemic, 300,000 people were living in lockdown conditions similar to solitary confinement, according to reporting by Keri Blakinger at The Marshall Project. Prison officials increasingly used lockdowns, creating solitary-like conditions with prisoners held in cells for most of the day, to try to curtail the spread of the virus within prison walls.

The authors of the recent Liman Center study note that their most recent survey snapshot, in July 2021, was during a lull in COVID infection rates.

The Liman Center survey does not capture estimates for prisoners held in solitary confinement in local jails. A recent estimate from Solitary Watch, a nonprofit that produces research and reporting on solitary confinement in the U.S., includes local jails but takes a broader definition of solitary confinement — namely, a prisoner being held in an isolated cell for 22 hours on any given day.

Solitary Watch estimates across jails and prisons roughly 122,000 prisoners were held in restrictive housing in mid-2019, according to a 2023 report from the group.

The analysis is based on federal and state data, as well as a survey of local jails conducted by the Vera Institute of Justice. It is the first to cohere estimates of solitary use in both prisons and jails. Roughly 6% of prisoners held in federal prisons and jails, state prisons and local jails are held in solitary confinement at any given time, according to the Solitary Watch analysis.

A recent analysis of prisoner data by NBC News senior reporter Erik Ortiz finds that as of September 2022, there were 11,368 out of 142,000 federal prisoners held in restrictive housing, up 7% from May of that year.

Segregated, isolated housing situations are not limited to prisoners encountering the traditional criminal justice system. Officials at U.S. Immigration and Customs Enforcement detainment facilities can hold noncitizens in conditions similar to solitary confinement — in cells separated from the general population of detainees for up to 24 hours a day, according to a 2022 report from the Government Accountability Office.

The federal government watchdog estimates ICE made 14,581 segregated housing placements from 2017 to 2021. “About 40 percent of these placements were for disciplinary reasons, such as drug possession, and about 60 percent were for administrative reasons, such as protective custody or medical reasons,” according to the report.

The demographics of solitary confinement

A November 2020 report, led by Florida State University criminologist Daniel Mears and funded by the National Institute of Justice, offers insight into who is typically held in solitary using administrative records for 184,183 prisoners in Florida correctional facilities from 2007 to 2015.

Long-term solitary confinement of over six months is more common among prisoners who are younger, Black and male, the report finds. Those held in long-term solitary “also consisted of a higher percentage of individuals who had been incarcerated for violent crimes (54.9% vs. 27.7%), who had been assigned longer sentences (45.6 months vs. 31.6 months), who had been diagnosed with a mental illness (28.9% vs. 15.0%), and who needed mental health services (31.1% vs. 16.6%),” the authors write.

Another paper, published November 2021 in Science Advances, analyzes Pennsylvania prison records from 2007 and 2016 and estimates that almost one in five Black men born in the state from 1986 to 1989 had been incarcerated by age 30.

The authors also find high relative rates of Black men born during those years who were held in solitary confinement, which they define as being held in solitary for at least a full day.

“Estimating the population prevalence, we find that 11% of all black men in Pennsylvania, born 1986 to 1989, were incarcerated in solitary confinement by age 32,” the authors write. “Reflecting large racial disparities, the population prevalence is only 3.4% for Latinos and 1.4% for white men. About 9% of black men in the state cohort were held in solitary for more than 15 consecutive days, violating the United Nations standards for minimum treatment of incarcerated people.”

The authors find that this racial disparity is driven less by choices that prison officials make on who ends up in solitary, and much more so by systemic factors — namely, that Black and Latino men are generally at a higher risk of incarceration than white men. 

Research also suggests solitary confinement does not usually work to deter future rule breaking — though there may be individual cases in which someone held in solitary for a length of time shows improved behavior upon return to the general population.

One analysis, published January 2019 in Criminal Justice and Behavior, looks at data on more than 9,000 prisoners who spent at least one day in restrictive housing from 2007 to 2010 in a Midwestern prison. The authors, Ryan Labrecque and Paula Smith, find no association between time spent in solitary and later infractions, both violent and nonviolent.

Click to see Ryan Labrecque discuss his years of research on restrictive housing.

“At the end of the day, my research and professional experiences have led me to this conclusion, that restrictive housing is just not an effective strategy for improving individual behavior,” said Labreqcue, a former corrections officer who is now a senior program manager at RTI International, during a symposium on solitary confinement hosted last fall by the John Jay College of Criminal Justice.

The mental and physical toll

Mental health problems, such as post-traumatic stress disorder, and physical issues, such as musculoskeletal pain and cardiovascular hypertension, are well documented in the academic literature as consequences of long-term solitary confinement.

But much of the research on the mental health effects of solitary confinement is based on small samples or is anecdotal, as Columbia University clinical psychologist Elizabeth Ford noted during the John Jay symposium.

“We really don’t know — we do not know — the full impact of what the practice of confining people, who are already confined, has on mental health at any kind of large population level,” Ford said.

Long-term solitary confinement usually falls under the administrative segregation umbrella and can last anywhere from several weeks to years. Research has found those held in solitary are at higher risk for early death.

Prisoners who have spent any time in solitary confinement are 24% more likely to die within the first year after their release from prison, compared with prisoners who never experienced solitary confinement, according to a 2019 study of nearly 230,000 former prisoners in North Carolina, published in the Journal of the American Medical Association.

Click to see Elizabeth Ford discuss her work with people who have experienced solitary confinement.

Those prisoners held in solitary were 78% more likely to die by suicide and 54% more likely to die by homicide within the first year after release — and “127% more likely to die of an opioid overdose in the first 2 weeks after release,” the authors write.

Research also suggests a link between existing mental illness among prisoners and the use of solitary confinement. Prisoners with a serious mental health diagnosis, such as major depression or schizophrenia, are 170% more likely to end up in long-term solitary confinement, according to an analysis, published in 2022 in Justice Quarterly, of more than 155,000 male prisoners who entered correctional facilities in a large southern state from 2007 to 2015.

The Mississippi State Penitentiary in Parchman, the state’s only maximum security prison, is a case in point. Of the 12 prisoners who have died by suicide there since 2019, all were being held in restrictive housing, according to an investigatory report by the U.S. Department of Justice published in April 2022.

“I don’t think we talk enough about what happens to a person’s brain when they are under chronic stress — chronic, it’s not letting up for years — and isolated with a lack of access to the thoughts and behaviors of other people.” Ford said. “We’re social beings. To not be able to reflect how you feel against another person’s opinion or thoughts is extraordinarily damaging.”

A brief history of long-term solitary confinement

In America’s early days, penal punishment was physical punishment, and included whippings, brandings and executions. Prisoners were held in dungeon-like conditions.

The notably pacifistic Quakers, a Christian religious group tracing to the 1650s in Britain, proposed an alternative punishment scheme for criminals, based on quiet self-reflection.

In the 1790s, the state of Pennsylvania took control of the Walnut Street Prison, previously run by the city of Philadelphia. Walnut Street became the third state-run prison in U.S. history and adopted what was a radical stance toward criminal punishment, influenced by Quaker philosophy.

Walnut Street was considered a model of humane prisoner treatment, with 16 solitary confinement cells, according to a 2018 paper by Reiter and Ashley Rubin, a sociologist at the University of Hawaii at Mānoa, and published in the journal Law & Social Inquiry.

“The notion at the time was that providing a space for silent, solitary reflection and penitence would result in rehabilitation,” a group of twelve Connecticut-based Quakers write in an essay published in the CT Mirror 2021. “Instead, the stark isolation caused people to deteriorate mentally and physically.”

The Walnut Street experiment failed in its goal of helping prisoners achieve discipline through self-examination — there was overcrowding, the solitary cells were used as a last resort, and there were riots and escapes, according to Reiter and Rubin.

Over the following decades, experiments with long-term solitary confinement at Western State Penitentiary in Pennsylvania, Auburn State Prison in New York and Maine State Prison were derailed by poor physical design. Cells were not only cramped but also poorly ventilated, forcing officials to release solitary prisoners from segregation.

“By the middle of the 1820s, penal reformers and prison administrators alike expressed intense opposition to total solitary confinement,” write Reiter and Rubin. “Most centrally, they concluded that the practice was cruel and inhumane and dangerous to mental and physical health.”

Solitary use persisted in Pennsylvania until the latter half of the 19th century, but by the late-1800s influential U.S. institutions, such as the Supreme Court, were decrying the use of long-term solitary confinement.

For much of the 1900s, solitary confinement was still used, but the extent is unclear. Reiter and Rubin note that records from Alcatraz, the federal prison in San Francisco that operate from 1934 to 1963, show unruly prisoners were placed in dungeon-like conditions.

The COVID-19 pandemic was not the first time prisons imposed conditions akin to solitary confinement for stated public health reasons. In the mid-1980s, 46 out of 51 state and federal prison systems allowed prison officials to segregate people living with HIV, according to a May 2023 commentary in the journal Health Affairs.

The ‘supermax’ era of solitary confinement

The systematic, institution-level use of long-term solitary confinement began in California with the opening of Pelican Bay State Prison in 1989.

Known as a super-maximum security, or “supermax” prison, Pelican Bay was built, and still operates, with more than 1,000 solitary confinement cells. Supermax prisons are typically defined by segregated, isolated cells intended to house prisoners for years.

In an article published in the Los Angeles Times when Pelican Bay opened, a reporter for the Los Angeles Times described the new supermax “as sterile and aseptic as a hospital, an Orwellian prison of the future,” and quoted a psychology professor who warned that the “isolation is so extreme that many could suffer severe psychological problems that could turn them into even bigger security risks and significantly reduce their chances for rehabilitation.”

Pelican Bay ushered in a new era of long-term solitary confinement in penal institutions. Its construction came on the heels of incidents in the early 1980s at a federal prison in Marion, Illinois, in which prisoners killed two guards.

“There is no way to control a very small subset of the inmate population who show absolutely no concern for human life,” former Federal Bureau of Prisons director Norman Carlson told the San Francisco Chronicle in 1998. “These two characters (who killed the two guards) had multiple life sentences. Another life sentence is no deterrent.”

By the mid-2000s there were 25,000 supermax prisoners across 44 states, according to 2006 research by Mears, funded by the National Institute of Justice.

“From the mid-1990s and throughout the 2000s, supermaximum security (or ‘supermax’) prisons, designed specifically to hold many hundreds of people each in strict and prolonged solitary confinement, proliferated across the United States,” writes Sharon Shalev, a research associate at the Centre for Criminology at the University of Oxford, in a 2022 article published in the journal Torture.

There is a lack of current, national counts or estimates of the prevalence of supermax prisons or units. Whether or not a state has a dedicated supermax facility, states typically allow for administrative segregation for safety reasons and for prisoners waiting for a disciplinary hearing or investigation, according to a review of state policies published in 2021 in the Criminal Justice Policy Review.

“Supermax housing illustrates a policy that was implemented with little credible research to establish its need or effectiveness,” said Florida State’s Mears during a 2022 speech to the Academy of Criminal Justice Sciences. “Given what amounts to a recurring fixed cost, it precludes prison systems from investing the funds in other policies. And, ironically, it may contribute to the very problems that it was designed to alleviate.”

Today, the federal government operates one dedicated supermax prison, located in Florence, Colorado. It houses 320 prisoners, among them high-profile criminals convicted of federal crimes. Notable prisoners include 2013 Boston Marathon bomber Dzhokhar Tsarnaev; Terry Lynn Nichols, who helped Timothy McVeigh make the bomb McVeigh exploded at a federal building in Oklahoma City in 1995; and Mexico-based drug cartel leader Joaquin ‘El Chapo’ Guzman.

The economic costs

Research shows that holding a prisoner in long-term solitary confinement is more expensive than keeping them in the general prison population. Amid statewide budget crunches and high relative financial costs of building and operating them, some states in recent years have closed their supermax prisons or units.

For example, Illinois in 2013 shuttered its Tamms Correctional Center, which cost $26 million per year to operate and included a 500-bed supermax unit.

More recently, in 2021, Connecticut closed its lone supermax prison, Northern Correctional Facility in Somers.

“The operational costs associated with Northern Correctional exceed most other locations, and the overall census has not surpassed one hundred inmates in the last six months,” Angel Quiros, Commissioner of the Connecticut State Department of Correction, said in a statement at the time of the closure.

Though much of the research on the costs of supermax prisons was published during the 2000s, supermax prisons are widely known to be costlier than traditional prisons.

With individual cells and enhanced security requirements, supermax prisons usually are two to three times costlier to construct and run than maximum security prisons, according to the 2006 report by Mears.

A February 2023 policy brief by senior researcher Tonya Lindsey of the California Research Bureau, a state-funded organization that provides public policy analysis to elected officials, estimates that California could save $63 million per year by severely curtailing or eliminating restrictive housing.

Recent research also identifies economic costs to broader society from the use of solitary confinement. One way this plays out is through recidivism, which refers to someone convicted of a crime encountering the criminal legal system again.

A 2022 meta-analysis published in the journal Trauma, Violence & Abuse, finds that prisoners held in long-term solitary confinement were more likely than general population prisoners to encounter the criminal justice system again, and twice as likely to recidivate if they were released from prison within 90 days of being held in solitary.

Aside from the established mental health consequences of solitary confinement, the authors also suggest that because prisoners held in solitary are often not allowed education or job training opportunities, they are less ready to find a job after release.

“In these ways, [solitary confinement] not only fails to fulfill a rehabilitative mission but could also create additional financial and health costs to society,” the authors conclude.

The November 2020 report led by Mears and focusing on prisoners held in Florida prisons finds those prisoners released directly from solitary confinement and into free society were 52% more likely to encounter the criminal justice system again than those who were never held in solitary, who had a 40% chance of recidivism.

Alternatives to solitary confinement

For prisoners who feel unsafe in the general population, one alternative to placement in solitary confinement is called open protective custody. This is a separate unit where prisoners who require separation from the general population are housed together. Some, though not all, prisons offer open protective custody.

“It’s an open unit, they’re just isolated to themselves and no one is allowed to have access to that group or that unit because they truly are in there for their own protection,” said Brian Koehn, a former prison warden in the southwest, during the John Jay symposium.

“Many of them have convictions of sexual offenses, some of them are gang member dropouts, or some of them just owe money and they can’t pay it and they’re afraid for their lives,” Koehn added.

At the same time, those who have worked in prison systems say there is always a subset of prisoners who are ungovernable if left among the general population.

Click to see Brian Koehn discuss his experience as a prison administrator.

Labrecque noted that what is often missing from conversations about solitary confinement among policy makers and in the media is that there legitimately are violent individuals who make life unsafe for a general prison population — but what else could be done in lieu of placing those individuals into strict solitary confinement?

He suggested that prison systems consider these four ways to minimize and improve the use of solitary confinement:

  • Narrow the pathways to solitary confinement — the placement criteria — so minor rulebreakers don’t end up there for long periods of time.
  • Put reasonable time limits on the length of time a prisoner can be segregated, and allow prisoners to earn their way out of segregation through good behavior.
  • Improve conditions within solitary confinement — allow access to rehabilitative programming and allow for more opportunities for social interactions.
  • Focus on prevention with case management and treatment targeted to those prisoners who are more likely after intake to end up in solitary.

“One of the things that continues to baffle me in U.S. corrections is that we have a group of people in restrictive housing who are arguably at the highest risk, and most in need of treatment services, yet because they are in restrictive housing, they are least likely to get those needed services and interventions,” Labrecque said.

At least one recent study, published in December 2021 in The Prison Journal, explores perspectives on solitary confinement among prison officials and corrections officers.

The authors conducted focus groups with 144 of these officials and officers working in prisons in a large southern state. Many of them echoed Labrecque’s assessment that more constructive programming is needed for prisoners being held in solitary.

Nearly all of the officials and officers interviewed agreed that mentally ill prisoners are more likely to end up with serious rules violations or otherwise be too difficult to handle in the general population — and more likely to end up in solitary confinement.

The stress of trying to manage individuals in restrictive housing spilled over into the everyday lives of many of the officials and officers interviewed.

“They perceived everyone as a potential danger or as likely to be lying to or manipulating them,” the authors write.

Several of the officials and officers acknowledged the physical and mental tolls borne by prisoners in solitary. They emphasized that solitary confinement is a critical tool used to maintain prison order, but also suggested increased staffing within general populations would limit the use of restrictive housing.

“Wardens, supervisors, officers, and staff consistently expressed a concern that echoed frequent critiques of restrictive housing — namely, nothing about the time spent there addresses inmates’ needs in any appreciable way,” the authors write. “The cause was attributed primarily to the lack of programming and treatment, both of which are severely restricted in this housing.”

Further reading


Revisiting and Unpacking the Mental Illness and Solitary Confinement Relationship
Sonja Siennick, Mayra Picon, Jennifer Brown and Daniel Mears. Justice Quarterly, February 2021.

The Impacts of Restrictive Housing on Inmate Behavior, Mental Health, and Recidivism, and Prison Systems and Personnel
Daniel Mears, et. al. Florida State University research report, January 2021.

The Body in Isolation: The Physical Health Impacts of Incarceration in Solitary Confinement
Justin Strong, et. al. PLOS One, October 2020.

Association of Restrictive Housing During Incarceration With Mortality After Release
Lauren Brinkley-Rubinstein, et. al. Journal of the American Medical Association, October 2019.

Assessing the Impact of Restrictive Housing on Inmate Post-Release Criminal Behavior
Kristen Zgoba, Jesenia Pizarro and Laura Salerno. American Journal of Criminal Justice, August 2019.

The Cardiovascular Health Burdens of Solitary Confinement
Brie Williams, et. al. Journal of General Internal Medicine, June 2019.

Assessing the Impact of Time Spent in Restrictive Housing Confinement on Subsequent Measures of Institutional Adjustment Among Men in Prison
Ryan Labrecque and Paula Smith. Criminal Justice and Behavior, January 2019.

History of Solitary Confinement Is Associated with Post-Traumatic Stress Disorder Symptoms among Individuals Recently Released from Prison
Brian Hagan, et. al. Journal of Urban Health, March 2017.


Immigration Detention: Actions Needed to Collect Consistent Information for Segregated Housing Oversight
U.S. Government Accountability Office, October 2022.

Illuminating the “Dark Figure” of the Most Extreme Forms of Incarceration
Jennifer Brown, Daniel Mears, Vivian Aranda-Hughes and Sonja Siennick. Criminal Justice and Behavior, June 2022.

The population prevalence of solitary confinement
Hannah Pullen-Blasnik, Jessica Simes and Bruce Western. Science Advances, November 2021.


The Impacts of Restrictive Housing on Inmate Behavior, Mental Health, and Recidivism, and Prison Systems and Personnel
Daniel Mears, et. al. Florida State University research report, January 2021.

Opening the Black Box of Solitary Confinement Through Researcher–Practitioner Collaboration: A Longitudinal Analysis of Prisoner and Solitary Populations in Washington state, 2002–2017
David Lovell, et. al. Justice Quarterly, December 2020.

History and perspectives

Views From the Inside: Insights About Restrictive Housing From Prison System Officials, Officers, and Staff
Daniel Mears, George Pesta and Vivian Aranda-Hughes. The Prison Journal, December 2021.

Continuity in the Face of Penal Innovation: Revisiting the History of American Solitary Confinement
Ashley Rubin and Keramet Reiter. Law & Social Inquiry, December 2018.

Reducing Institutional Disorder: Using the Inmate Risk Assessment for Segregation Placement to Triage Treatment Services at the Front End of Prison Sentences
Ryan Labreqcue and Paula Smith. Crime & Delinquency, December 2017.

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