Prisoners are acting as untrained carers for elderly inmates in the North as the pensioner population behind bars swells.
Almost 70 are aged over 60 and the oldest is in his early 80s.
A surge in the number detained and sentenced for historic sex offences means dementia inside jail is likely to become more of a challenge in the next few years, a watchdog said.
The Independent Monitoring Board (IMB) for Northern Ireland warned social care had been "batted" between the prison and health authorities amid reduced staffing levels.
It added: "Prisoners have been acting as carers, not, we would point out, carrying out any personal care, for some of the more severely disabled or disorientated prisoners."
They clean cells, wash laundry and collect their food.
A healthcare worker attends prison twice daily to attend to the personal care of one prisoner.
The Board added: "While the prisoners who do these tasks carry out an at times unenviable role there will always be risks attached, a possible one being taking medication belonging to prisoner being cared for and as in the community there is always risk of abuse of a vulnerable individual.
"There is also no training given to carers in working with vulnerable adults."
Some life sentenced prisoners are nearing the end of their terms for crimes committed while aged in their 40s or 50s.
They face the same age-related problems as in the community: dementia, mobility issues, Parkinson's Disease, incontinence, and also in many case ill-health as a result of years of chronic alcohol and/or drug abuse, chaotic lifestyles and poor diet.
Some had no permanent address so missed out on even routine health checks.
The IMB said prison staff were not medically trained to deal with elderly prisoners' health problems and could not deal with personal care issues.
"While staff do a good job as far as they can and in one particular area of the prison which houses the most vulnerable elderly they do an excellent job, they are also trying to care for increasing numbers with reduced staffing levels and less experienced staff.
"On the primary nursing care side South Eastern Trust have problems recruiting and retaining staff and the mental health team are also understaffed.
"Staff can ask prisoners to wash but they do not have the power to make them wash so this can lead to serious issues around hygiene which not only affects the prisoner but other prisoners and staff."
The IMB said it was very unfortunate that no provision for social care was agreed when the Trust took over the healthcare element of the Northern Ireland Prison Service.
"This has now led to a position where neither the NIPS nor the Trust have budgeted for this."