Of the 14 and a half months, or 9,840 hours, I was held as a political hostage at Evin prison in Tehran, I spent 9,495 of them in solitary confinement. When I was released just over a year ago, I was shocked to find out that the United Nations Convention Against Torture, one of the few conventions the United States has ratified, does not mention solitary confinement. I learned that there are untold numbers of prisoners around the world in solitary, including an estimated 20,000 to 25,000 in the United States. According to the United Nations’ special rapporteur on torture, Juan Méndez, the practice appears to be “growing and diversifying in its use and severity.”

Amy Fettig at the American Civil Liberties Union told me: “In the U.S. we use solitary as a routine prison administrative practice. It’s not something that’s used as a last recourse, as it should be.” Last summer, prisoners at Pelican Bay prison in California went on a hunger strike to end the practice of isolating some prisoners for more than 22 hours a day. The strike spread until thousands of prisoners were participating. Only when officials agreed to review the use of solitary confinement did the prisoners accept food.

Such a review is needed for prisons everywhere, and particularly in the United States, the country with, according to Ms. Fettig, the most prisoners in solitary confinement in the world. One of the problems, according to Mr. Méndez, is that there is no universally accepted definition of solitary confinement. Mr. Méndez and his staff defined it as “more than 22 to 24 hours isolated from anyone else except for guards.” They are calling for clearer standards regarding “what is disciplinary and what moves into the category of ‘severe pain and suffering, either physical or mental,’ which is definitely prohibited under international law.” He has called for a ban on prolonged solitary confinement, and I very much agree. Any case that lasts more than 15 days should be carefully investigated.

You don’t have to beat someone to inflict pain and suffering; the psychological torture of prolonged solitary confinement leaves no marks, but its effects are severe and long-lasting. Fortunately, the guards did come that winter day. Once I began to have short daily visits with Shane and Josh, my mental health improved, but only marginally. At that point I was sunk so deep inside myself that there were days when I was brought out to visit them and couldn’t communicate or even look them in the eyes. After prison, I was diagnosed with post-traumatic stress disorder. I still pace and wring my hands when I am nervous; I still have nightmares and trouble sleeping. I stopped going to a certain exercise class because the texture of the ceiling reminded me of the ceiling in my cell.