Sexually transmitted infections are increasing among middle-aged women, two experts in the field have warned.
Sexual health messages "largely ignore" older women, experts say
They say post-menopausal women are not included in the safe sex message, as it is wrongly assumed they are low risk.
The doctors, from the Radcliffe Infirmary in Oxford, warn older women are actually more susceptible to diseases, including HIV.
The research by Dr Faryal Mahar and Dr Jackie Sherrard is published in the book Sexual Health and the Menopause.
Barrier contraception is the only way to prevent the transmission of sexually transmitted infections (STIs), including HIV.
But the doctors say that as pregnancy is not an issue for post-menopausal women, many do not use condoms.
Rates of STIs have risen in all age groups over the last decade.
But figures from the Health Protection Agency for England, Wales and Northern Ireland show that, among women aged 45 to 64, rates of chlamydia rose by 177%, from 150 to 416 cases, between 1995 and 2003.
Cases of gonorrhoea among women in that age group rose 249%, from 39 to 136.
In 2003, women over 40 made up 7% of patients diagnosed with HIV, up 2% from 2001.
While the actual numbers affected are small, the researchers say the rises show that age group is increasingly at risk and need to be targeted with health information.
The experts, writing in the book published by the Royal Society of Medicine Press, say all adults over 45 are "universally omitted from prevention programmes", even though they are physiologically predisposed to STI infections.
Menopausal women in particular have "largely been ignored in the field of sexual health", they say.
They suggest women in this age range are seen as a low-risk group - considered to be either in monogamous relationships or relatively sexually inactive. However a growing number are beginning new relationships later in life.
The researchers said they were also at risk because of changes to the vagina as women age.
Oestrogen deficiency means vaginal and cervical tissue becomes more fragile. This can result in tears or abrasions which lead to increased susceptibility to STIs.
Dr Sherrard told the BBC News website: "This is about increasing awareness among both women and healthcare professionals.
"These were young before the 'don't die of ignorance campaigns', so condom use isn't something they're necessarily informed of or skilled at negotiating."
She added that doctors did not necessarily consider STIs when treating menopausal women, and that symptoms of the menopause could mask signs of infection.
"The possibility of women having new relationships is not the first thing that comes to mind," she said.
"But women may well have come to the end of a long-term relationship. They find new ones and don't think they need contraception."
Jo Robinson, of the Terrence Higgins Trust, said most cases of HIV infection, as well as other STIs, occurred in younger people.
But she added: "There is an over-emphasis on young people.
"It can be quite hard to talk about older women and sexual relationships. There's a real taboo about seeing women as sexual beings."
The researchers say middle-aged men are also at risk, but that they often do not even consult a doctor.