The over-45s are "apparently oblivious" to the need to use condoms in a new relationship, a charity has warned.
Almost 13,000 men and women over 45 were diagnosed with a sexually-transmitted infection (STI) last year - double the number in 2000, according to UK data analysed by the Family Planning Association (FPA).
More men over 45 got genital herpes in 2009 than men aged 16 to 19, while in excess of 5,000 men and women over 45 were diagnosed with genital warts in the same year.
The number of cases of chlamydia among women over 45 has also shot up 95% in nine years.
Furthermore, calls to the FPA helpline from older people worried about STIs and their risky behaviour have risen 30% in three years.
The charity has now launched a campaign to highlight the issue, called The Middle-age Spread, targeted at older age groups but particularly the over-50s.
It said people coming out of long-term relationships are using websites, social networks and holidays to date again but too many are "apparently oblivious to the need for safer sex and the importance of condoms".
Julie Bentley, chief executive of the FPA, said this group was also more likely to be embarrassed about STIs and therefore less likely to seek help. "There is very little sexual health information and services for this age group, and current campaigns, however good, are exclusively for the young," she said.
"Sex is something very personal, we can all find it difficult to talk about and this can be particularly true for older generations.Many people, relieved contraception is no longer an issue, forget about using condoms. Others haven't had to think about using condoms for decades, let alone go into a shop and buy them. Worries about confidentiality stop them going to clinics which tend to be more geared for young people.
"We celebrate the positive and fulfilling sexuality of the over-50s, but we also have to get the message across that STIs don't care about greying hair and a few wrinkles. This is a concerning situation which unless we take action now is only going to get worse."