Sexually transmitted infections (STIs) are diseases passed on through intimate sexual contact.

They can be passed on during vaginal, anal and oral sex, as well as through genital contact with an infected partner. Common STIs in the UK include chlamydia, genital warts and gonorrhoea.


How common are they?

In the UK, the incidence of STIs has been rising since the 1990s. Between 2007 and 2008, the Health Protection Agency (HPA) reported a 0.5% increase in the number of diagnosed STIs, with a total of 399,738 new cases reported in 2008.

The biggest increase was in the number of confirmed diagnoses of genital herpes, which rose by 10% to a total of 28,957 cases. There were also increases in diagnoses of genital warts and chlamydia.

The numbers of diagnosed cases of STIs are still going up and the age group most affected continues to be 16 to 24-year-olds. Even though they make up just 12% of the population, young people account for more than half of all STIs diagnosed in the UK. This includes 65% of new chlamydia cases and 55% of new cases of genital warts.