(Whitney Shefte/WASHINGTON POST)

THE UNITED States is a world leader in solitary confinement, a degrading assault on the mind that the Supreme Court came close to declaring unconstitutional in 1890.

You wouldn’t know this from state corrections departments. Arizona, for example, insists that “no such confinement exists in our institutions” — even though the state just agreed to alleviate the isolation it enforces on thousands of prisoners under a new settlement with the American Civil Liberties Union. Maryland, as the Baltimore Sun has repeatedly noted, prefers terms such as “disciplinary segregation” and “administrative segregation.” These programs pull in about 8 percent of the state’s prison population, most of them for violating prison rules, according to a 2012 internal state analysis we obtained.

No matter what officials call it, Arizona is being forced to make some changes. Maryland, on the other hand, is having trouble even holding a debate on the issue, thanks to the General Assembly.

After we wrote about the Arizona case last week, we published a letter from Susan Kerin of Interfaith Action for Human Rights noting that Maryland lawmakers recently scuttled a bill calling for an independent analysis of the state’s use of prisoner segregation. The bill merely asked for a report on living conditions and the frequency with which state facilities isolate prisoners. It sought recommendations on how to reduce the number of prisoners in isolation, how to improve conditions and how to manage juveniles and the mentally ill. All of these goals should be priorities for any state that claims to run a humane prison system.

Many corrections officials insist that some prisoners have to be separated to prevent violence. Maryland officials also point out that many of those in what they call segregated housing have cellmates, so true long-term solitary confinement is rarer than critics suggest.

But is it rare enough? Weeks, months and years of solitary confinement can destroy people’s minds. Stories of healthy inmates leaving solitary with a mental illness are horrible but unsurprising. So are accounts of inmates who enter it with a mental illness and come out worse — if they don’t commit suicide, a particular problem in isolation programs.

Isolation can seem like an easy solution for dealing with a violent or antisocial inmate, but it can be expensive and counterproductive, deepening the psychosis that led to bad behavior. The internal report found that isolated prisoners in Maryland face “heightened risk for worsening physical and mental health outcomes.”

Paul Smith is a mentally ill prisoner in Maryland whose parents told reporters last year that he had been held in solitary confinement for four years; during two of them, he hadn’t been allowed visitors or phone calls. Mr. Smith’s parents finally got to see him after WUSA-TV reported on his case. Unsurprisingly, they found that their son’s bad mental state had worsened.

Prisons should isolate inmates only in rare cases when that is the singular way to prevent violence. The General Assembly should ensure that Maryland abides by this principle, rather than hiding behind euphemisms.