The number of people diagnosed with sexually transmitted infections (STIs) rose by almost 500,000 last year, with cases of chlamydia and gonorrhoea seeing the biggest increase.
A study from the Public Health England (PHE) showed that STI diagnosis rose by 5% in 2012 from the previous year, with people under the age of 25 most at risk.
The number of new gonorrhoea diagnoses increased by 21%, which is particular cause for concern among health officials as the global threat of antibiotic resistance grows.
Almost half the infections were chlamydia, which amounted to 46% of the total diagnosis. Known as the "silent infection" because it can go unnoticed, non-treatment of chlamydia can lead to pelvic inflammatory disease (PID) and damage in women's reproductive system.
The study suggests too many people are still putting themselves at risk through unprotected sex, especially young adults and 'men who have sex with men' (MSM).
Those under 25 experienced the highest rates of STIs, contributing 64 per cent of all chlamydia and 54 per cent of all genital warts diagnoses in heterosexuals in 2012. New gonorrhoea diagnoses also rose 37% in the MSM population.
Dr Gwenda Hughes, PHE head of STI surveillance, said: "There have been significant improvements in screening in recent years, particularly for gonorrhoea and chlamydia among young adults and men who have sex with men, so we are diagnosing and treating more infections than ever before.
"However, these data show too many people are continuing to have unsafe sex, put themselves at risk of STIs and the serious consequences associated with infection, including infertility.
"Ongoing investment in programmes to increase sexual health awareness, condom use and testing, particularly for groups at most risk, is vital."
Lisa Power, policy director at the Terrence Higgins Trust, said the 21% rise in gonorrhoea was particularly worrying.
She said: "It is vital that people, particularly young people starting their adult lives, understand how to prevent sexual ill-health. This includes using condoms and going for regular check-ups as well as valuing the importance of healthy relationships."
Hughes added more needs to be done to stop the rise in the number of chlamydia diagnosis.
"We must also ensure chlamydia screening remains widely available," she said.
"Local authorities should continue to integrate chlamydia screening into broader health services for young adults.
"This will also help this age group develop positive relationships with services, enabling them to develop and maintain good sexual health throughout their lives."