Chlamydia
The most common bacterial, sexually transmitted infection in the UK. In England alone, cases have more than doubled in the five years from 1996 so that by 2001 nearly 30,000 men and 40,000 women were diagnosed with the condition. The infection is difficult to diagnose because it often produces no symptoms, but at its worst chlamydia can cause infertility in women.

Gonorrhea
Male cases doubled over five years so that by 2001 nearly 15,500 infections were being diagnosed. Gonorrhea has similar effects to chlamydia, causing pain and irritation in men and creating a risk of infertility for women, whose cases of the infection rose by 67% over five years. There is increasing concern that the bacterium might be becoming resistant to antibiotics.

Syphilis
The number of cases has rocketed across the board, with cases among homosexuals rising by 1605% - albeit from a very low baseline so that by 2001 there were still only 341 cases diagnosed. Male cases in general increased seven-fold in five years and female cases tripled - although there were still less than 700 cases identified in total. Symptoms include lesions and a rash and can lead to disability and death if not treated.

Genital warts
The most common of the viral sexually transmitted diseases, genital warts can cause itching and irritation unless treated with a chemical paint or freezing the warts. There were only modest increases in this condition with men seeing diagnoses rise by 20% over five years - a total of 32,636 cases were found in 2001.

Genital herpes
This is a common infection that can be caught through oral or penetrative sex with symptoms that include small blisters and difficulty or pain in passing urine. Herpes also causes cold sores and is a life-long condition, but the severity and recurrence of infections can be decreased by using drugs. Diagnoses rose by over 10% for both men and women.

Human immunodeficiency virus (HIV)
HIV infections are also rising, with an estimated 6,500 new cases diagnosed last year. The virus prevents the immune system from working properly by infecting the cells that coordinate the fight against infection.