Almost one-third of prisoners who are locked up 23 hours a day are aged 18-24, campaigners have revealed.
The Jesuit Centre for Faith and Justice said there is no reason the State cannot halve the number of young people being sent to jail and put into severe confinement, many out of fear for their own safety.
Its research showed 18-24-year-olds make up about 12% of the country's population but a quarter of those are sent to prison each year.
Statistics for January from the Irish Prison Service showed that 17 young adults were on extended lock-up with only one hour a day out of their cells. They make up almost one-third of the total on this restrictive regime.
Another 75 were on 21 hours lock-up and 12 on 22 hours lock-up.
Fr Peter McVerry, homeless and addiction campaigner who visits Mountjoy and Wheatfield prisons each week, said: "Most young people in prison have left school early, have no qualifications or skills, often poor literacy skills, no history of employment. Indeed they have been failed by all the systems in society.
"It should be a priority to ensure that their time in prison is used constructively, by equipping them for life outside prison through educational and skills training. Unfortunately, for many young people, they leave prison no more equipped for life than the day they entered prison."
Eoin Carroll, advocacy officer in the Jesuit Centre and lead researcher, said Ireland should follow the example of other countries and ask Minister for Children and Youth Affairs, Katherine Zappone, to take responsibility for 18-24-year-old prisoners.
The Jesuits' report also called for young adults to be imprisoned separately from older inmates.
It warned that a disproportionate number of 18-24-year-olds are put in "basic" accommodation in jails for behavioural issues, leaving them with less access to family visits and telephone calls.
Statistics from the Irish Prison Service showed 9% of young adults in jails are imprisoned under this regime, compared to 2.6% of over 25s, leaving them with only one half-hour visit a week.
Joanne O'Riordan, a campaigner and activist on disability rights, said: "As a baby my parents brought me to Fort Mitchel Prison, since closed, on Spike Island in Cork. The prisoners there - mainly in their early 20's - decided to organise a fundraiser for my family," she said.
"When my parents heard, they wanted to personally thank them. I spent a day playing with them in the prison. Such a gesture, prisoners raising money for someone, really challenges our perception about people in prison as being just bad."