Prisoners with illnesses face "daily discomfort" and a "fear of bullying", a study says.
Prison health care has often been criticised
A University of the West of England team found serious gaps in health care in prisons in the UK after interviewing 111 inmates across 12 jails.
Inmates faced long waits for doctors, were denied treatment as staff thought they were lying and lacked privacy, the Journal of Advanced Nursing reported.
NHS managers admitted there was a long way to go, but said care was improving.
Healthcare in prisons is now the responsibility of local health bodies called primary care trusts (PCTs), which have been given the job of ensuring an NHS standard of care in jails.
Control was gradually handed over from the prison service from 2003 to 2006.
The researchers interviewed prisoners towards the end of that handover.
The team found that many prisoners were forced to submit written applications to see doctors, facing long-waits in the process.
They also said there was a lack of understanding about chronic conditions such as diabetes.
Some people with diabetes were not allowed to keep their insulin and blood testing equipment with them, while other prisoners were forced to talk about conditions such as sexually transmitted infections in front of other inmates.
Other prisoners expressed concern that night-time health emergencies would not be handled promptly with doors only unlocked in the most serious circumstances.
And some said there was a feeling that some staff took a tough approach to all prisoners because of a fear inmates faked illness to avoid work.
An older, incontinent prisoner told researchers how he had to use a bin bag to protect his mattress.
And an inmate with diabetes said he regularly missed breakfast because he was only offered high-sugar cereals.
However, some prisoners did report they had better access to mental health services.
Lead researcher Jane Powell said: "Little account appeared to be taken of the specific needs of prisoners, which meant that they experienced daily discomfort, combined with fear of bullying."
William Higham, head of policy at the Prison Reform Trust campaign group, said services were improving since PCTs took responsibility for care, but there was "still a long way to go".
"The problem is that too often prisoners are treated as if they are trying to get one over on the staff, that they are not ill or do not have health needs."
Jo Webber, of the NHS Confederation, which represents PCTs, said: "I think everyone involved in care would acknowledge there is still some way to go.
"Prisoners often have complex health needs, but it is a challenge we are trying to meet."