Common causes are:

• gonococcal urethritis
• non-gonococcal or non-specific urethritis (NSU).

Gonococcal urethritis (gonorrhoea)

This sexually transmitted disease is caused by Neisseria gonorrhoeae.

• Incubation period: it usually takes two to five days from infection to symptoms. Without treatment, symptoms of urethritis (inflammation of the urethra) and purulent (pus-containing) discharge peak within two weeks.
• Symptoms: discharge occurs in 95 per cent of men and is purulent in 75 per cent, white or cloudy in 10 per cent and clear in 5 per cent. Recent urination can make the discharge appear less purulent. When the infection begins to resolve, the discharge changes from purulent to mucoid (mucus-like).
• Transmission: transmitted by sexual intercourse, including oral sex. Without treatment, the infection can continue for many months.
• Complications: spread up the urethra to the epididymis (sperm-storing tube connected to the testicles) is rare and infertility can be a rare late complication. Anal infection is common especially, but not only, when the infection is transmitted by anal intercourse. Bloodstream infection occurs in less than 1 per cent of patients, causing arthritis of the knees, wrists and hands plus fever, chills and skin lesions, usually papules or pustules (red or pus-containing raised spots or bumps) on the hands or feet.

Non-gonococcal or non-specific urethritis (NSU)

NSU is the most common form of penile discharge accounting for over 60,000 new cases per year in England alone. The number of cases has fallen slightly over the past three years. Men aged between 20 and 35 years are most commonly affected. Several different organisms ('bugs') can cause the syndrome:

• Chlamydia trachomatis (25-60 per cent).
• Mycoplasma genitalium (up to 25 per cent).
• Ureaplasma urealyticum (15-25 per cent).
• Trichomonas vaginalis (17 per cent).
• Herpes simplex (rarely).