Internet dating has been blamed
Sexually transmitted infections have doubled in under a decade in people over 45 and are now rising faster than in the young, research suggests.
The Health Protection Agency (HPA) study said internet dating and erectile dysfunction drugs were partly to blame.
Men were most likely to be affected, with increases in herpes, syphilis, gonorrhoea and genital warts.
The study, published in Sexually Transmitted Infections, looked at those attending sexual health clinics.
The number of sexually transmitted infections is rising in both young and old, despite sexual health campaigns urging people to avoid unsafe sex.
The HPA looked at people going to genito-urinary medicine (GUM) clinics in the West Midlands between 1996 and 2003.
The vast majority of these were younger people - accounting for more than 95% in 2003.
However, the proportion of over-45s rose during the sample period.
In total, 4,445 infections were detected in older people, with genital warts accounting for almost half of these diagnoses.
Herpes was the next most common, with one in five diagnoses.
Within the over-45 age group, men and people aged 55 to 59 were most likely to have a sexually transmitted infection (STI).
The overall rate of infections more than doubled over the eight-year period from 16.7 per 100,000 population to 36.3 per 100,0000.
This meant a significantly higher increase for older people compared with younger patients.
Dr Babatunde Olowokure, from the HPA's regional surveillance unit in Birmingham, said: "Sexual health strategies have rightly focused on the under-25s but our results indicate that sexual risk-taking behaviour is not confined to young persons but is also an increasing trend in the over-45s.
"Older people are increasingly likely to be single or undergoing relationship changes and are less likely to consistently use condoms, perhaps because the risk of pregnancy no longer exists.
"Increased international travel, internet dating, new drugs to counter erectile dysfunction and overlapping sexual networks may also be factors."
Julie Bentley, the chief executive of the sexual health charity FPA, said: "We've also noticed a rise in the numbers of over-45s phoning our helpline.
"Tragically, the sexual health of men and women of this age group is largely neglected and its something we are increasingly concerned about.
"Services are geared towards young people, campaigns are targeted at the under 25s so over-45s think that sexual health has nothing to do with them and don't even know when they're taking risks."
Lisa Power, of the HIV charity Terrence Higgins Trust, said: "Sex is not the preserve of the young and gonorrhoea and syphilis are no respecters of age.
"People coming out of long-term relationships may be unaware of the risks of not using a condom.
"Rates of infections are far higher than 10 or 20 years ago, so remember to use condoms and get a check up if you are concerned."
The government said using a condom was "relevant for anyone having unsafe sex... regardless of age".
A Department for Health spokesman said: "Information about safer sex is available to everyone who needs it and our target to offer appointments at GUM clinics within 48 hours by March 2008 has improved access for all."