The Peru Two required medical treatment in Virgen de Fatima prison after their flesh was bitten by bugs, it has emerged.
Michaella McCollum, from Dungannon, and Melissa Reid, from Lenzie, near Glasgow (both 20) are accused of attempting to smuggle cocaine worth more than £1.5 million out of the South American country.
The Co Tyrone model and her Scottish friend are being held at the assessment centre of the prison in Lima – which houses murderers and high profile terrorists – while they await trial, and could face 15 years in prison if found guilty.
In a television interview yesterday, Melissa Reid's distraught mother, Debra, revealed both young women needed injections to control swelling after suffering bad bites.
Mrs Reid said she was pleased the "very close" duo were being held together and confirmed they had to have cold showers among other tough conditions where they are currently being held.
They had previously complained about it being cold, having no blankets and poor quality food.
"They've actually been bitten by some bugs that are in the assessment unit they are being held in," Mrs Reid added.
"I believe they've had to have an injection to try and stop them from (swelling up)."
"Melissa is just happy to get a shower, but it is a cold shower – you can't get hot water.
"The language barrier (is difficult), she's determined to learn Spanish so she can speak to the guards and fellow prisoners.
"At the moment they are being held separately in an assessment unit, they haven't been in the full prison."
Michaella's sister Stephanie issued an online statement revealing the family speak to her by phone every day.
She said: "Conditions in the prison aren't bad, food, however, is very bad and at times cannot be consumed.
"She is trying to remain positive but is also being realistic in the fact that she may be there for a while.
Last week, Melissa's father William Reid said he wanted his daughter to plead guilty because the women's case is "indefensible".
Debra Reid said she believes Melissa and Michaella were threatened and coerced by gangsters into smuggling the cocaine, but she also wants them to plead guilty.
"They definitely had the drugs in their suitcases, that part they are guilty of, but I do believe they were coerced into it."
Mrs Reid was also asked about her husband William reportedly telling a newspaper "he's not 100% on their story".
She said: "It's not so much that he's not 100%, it's more the legal system over there is totally different to ours.
"If Melissa pleads guilty we'll get her home early."
If Michaella and Melissa plead guilty they could be back in Northern Ireland and Scotland, respectively, in 30 months.
Michaella and Melissa will go before a judge in Peru next Tuesday to give statements and to plead.
They could then be moved to another prison or to the main prison unit at Virgen de Fatima.
It may then take up to two years for their case to come before the courts.
STORY SO FAR
Michaella McCollum and Melissa Reid are accused of trying to smuggle 11kg of cocaine from Lima in Peru to the Spanish capital, Madrid.
The drug haul discovered in the women's luggage at Lima's international airport last month was cut with bicarbonate of soda and starch, and concealed inside porridge and jelly packets to mask the smell of drugs.