Women prisoners have been coerced into sex with staff in return for favours such as cigarettes or alcohol, the Commission on Sex in Prison has heard.
Assaults known as 'decrotching', where women prisoners forcibly retrieve drugs from another inmate's vagina, are also thought to have occurred in jails.
The findings are published in the Commission's second briefing paper, Women in prison: Coercive and consensual sex, which is released today (25 February).
The Commission, which comprises eminent academics, former prison governors and health experts, was established by the Howard League for Penal Reform.
It is the first-ever independent review of sex behind bars in England and Wales.
The Commission found that some women form relationships in prison as a source of comfort and support. However, some relationships can become coercive or abusive.
Although prison staff reported that women were more overt than men about their friendships with other prisoners, the Commission heard evidence that they might keep sexual relationships secret for fear of being separated.
Women have different sexual health needs to men and they are at greater risk of entering prison with a sexually transmitted infection such as HIV, the briefing paper states.
The report concludes that staff need training and guidance on how to support women, recognise bullying and identify relationships between prisoners.
Chris Sheffield, Chair of the Commission on Sex in Prison, said:
"This is the second in a series of briefing papers produced by the Commission.
"Women in prison are particularly vulnerable and more likely than men to have a history of being a victim of violence or sexual abuse.
"It is important that policies recognise these differences and are developed in order to protect the vulnerable.
"It is equally important that staff in women's prisons receive specific training on working with women."
The two-year Commission is looking at three broad themes – consensual sex in prisons; coercive sex in prisons; and healthy sexual development among young people in prison. It focused on adults during 2013 and will this year study issues affecting children.
The Commission's next seminar, focusing on boys' sexual health, is to be held next month.
Almost all people in prison will eventually return to the community, meaning that sexual health policies are important not just for inmates, but for the public as a whole.