Solitary confinement is the practice of isolating a prisoner in a small cell for 22 or more hours a day without meaningful human contact. In most facilities, that means 23 to 24 hours locked behind a solid metal door in a space roughly the size of a small bathroom, with a narrow window and a slot for passing food trays. The United Nations defines anything beyond 15 consecutive days in these conditions as “prolonged” solitary confinement and classifies it, along with indefinite solitary confinement, as a prohibited form of cruel, inhuman, or degrading treatment.
What the Conditions Look Like
A typical solitary confinement cell contains a bed, a toilet, and a sink. Lighting is often fluorescent and constant, or the cell may have no natural light at all. Human contact is limited to brief moments when staff deliver food trays or conduct mental health check-ins through the door. Recreation, when it happens, usually takes place alone in a small, enclosed outdoor area for about one hour per day.
The sensory environment is extreme in both directions. Prisoners report overwhelming, repetitive noise from slamming metal doors and ventilation systems, yet almost no variety in sound, sight, or social stimulation. There are often no mirrors. The combination of sensory monotony and sudden loud disruptions contributes to a specific symptom researchers call sensory hypersensitivity, where ordinary sounds or lights become physically painful after weeks or months of deprivation.
Why Prisons Use It
Correctional systems place people in solitary confinement for a range of reasons. The most commonly cited justification is safety: separating someone who has assaulted staff or other prisoners, or who faces threats from the general population. But solitary is also used as a disciplinary sanction for rule violations, including relatively minor infractions like possessing contraband or disobeying orders.
A 2016 Department of Justice review found that inmates facing legitimate safety threats were often held in conditions identical to those placed there as punishment. The review called for housing people in the least restrictive setting necessary and recommended banning solitary for low-level infractions entirely. It also emphasized that correctional systems should always be able to clearly articulate the specific reason for each person’s placement and continued retention in isolation.
How Many People Are in Solitary
In the federal prison system alone, the average daily population in special housing units reached 11,974 in 2023, an 18% increase from the prior year. That figure covers only federal facilities. State prisons and local jails hold their own isolation populations, and estimates of the total number of people in solitary confinement across the entire U.S. system have ranged from 80,000 to over 100,000 in various analyses over the past decade.
People with serious mental illness are dramatically overrepresented. In one detailed study of a state isolation unit, 19% of the population carried a serious mental illness designation, compared to about 9% in that state’s general prison population. Twenty-two percent had a documented suicide attempt at some point during incarceration, and 18% had other documented self-harm.
Psychological Effects
The mental health consequences of solitary confinement are well documented and severe. In a study of people held in isolation in Washington State, half showed clinically significant symptoms of depression, anxiety, or guilt. Eighty percent described the emotional toll as a dominant feature of their experience, and 73% described profound feelings of social disconnection.
Beyond standard psychiatric symptoms like anxiety, depression, paranoia, hallucinations, and aggression, researchers have identified effects that appear to be specific to solitary confinement itself. About one in four people in one study described a loss of identity, a feeling of no longer knowing who they are or being unable to maintain a coherent sense of self. Sixteen percent reported sensory hypersensitivity. These symptoms were linked directly to the conditions of confinement: the absence of mirrors made it impossible to see one’s own face, and the constant slamming of doors created a stress response that didn’t fade over time.
The emotional damage compounds with duration. People held for longer stretches develop more entrenched symptoms, and even after leaving isolation, many struggle to re-adapt to social environments, open spaces, and normal sensory input.
Physical Health Consequences
Solitary confinement also takes a measurable toll on the body. With little or no access to sunlight, prisoners in isolation are at high risk for vitamin D deficiency, which weakens bones and reduces muscle strength. A study of inmates found that one-third were vitamin D deficient overall, but those at maximum security levels (where isolation is most common) had significantly lower vitamin D than those in medium or minimum security. Black inmates at maximum security were roughly four times more likely to be vitamin D deficient than white inmates at the same level, reflecting both reduced sunlight exposure and biological differences in vitamin D synthesis.
The physical inactivity of spending 23 to 24 hours in a tiny space compounds the problem. Without regular movement, muscle mass declines, joints stiffen, and cardiovascular health deteriorates. Some former prisoners report lasting changes to their vision from years of only being able to focus on surfaces a few feet away.
What Happens After Release
Time in solitary confinement doesn’t just affect people while they’re inside. A meta-analysis covering nearly 200,000 inmates found that those who spent time in solitary were 67% more likely to commit a new crime after release compared to those who served their time in general population. Even after researchers controlled for other factors that predict reoffending, the association held, with a 41% increased risk. The relationship was dose-dependent: more days in solitary meant higher recidivism risk. And people released more recently from solitary, rather than those who had time in general population before release, were twice as likely to reoffend.
This pattern suggests that solitary confinement does not simply warehouse dangerous individuals; it actively makes reintegration into society harder. The social skills, emotional regulation, and stress tolerance that people need to function outside prison are precisely the capacities that prolonged isolation degrades.
Protections for Juveniles and Vulnerable Groups
In 2016, President Obama announced a federal ban on solitary confinement for juvenile offenders in federal prisons. Since then, 24 states and the District of Columbia have enacted laws limiting or prohibiting the practice for young people in detention. Seven states have passed outright bans or strict limits specifically for youth. Connecticut, for instance, prohibits holding any child in solitary confinement, though it allows brief “seclusion” periods with check-ins every 30 minutes.
The 2016 Department of Justice review also identified other vulnerable populations that require special consideration, including pregnant women, LGBTI inmates, and people with serious mental illness. For the last group, the contradiction is particularly stark: the people most psychologically fragile are overrepresented in the setting most likely to cause psychological harm.