Non-gonococcal urethritis - Causes of non-gonococcal urethritis

Non-specific urethritis (NSU) is most commonly caused by an infection, although there are many cases where no cause is found.

Although sexually transmitted infections (STIs) can cause NGU, it does not result from a gonorrhoea infection. Urethritis caused by gonorrhoea is called gonococcal urethritis.

Chlamydia

In men, chlamydia is thought to be responsible for up to 43 out of 100 cases of NGU. In women, about 4 in 10 cases of NGU may be caused by chlamydia.

Chlamydia is caused by Chlamydia trachomatis bacteria. It is an STI and is spread during unprotected sex (sex without a condom), including anal and oral sex.

Other infections

A number of other infections can cause NGU.

These include other bacteria that usually live harmlessly in the throat, mouth or rectum. They can cause NGU if they get into the urethra, which is the tube that carries urine from the bladder to the outside of the body. This can occur during oral or anal sex.

Infections that can cause NGU include:

• Trichomonas vaginalis – which is an STI caused by a tiny parasite
• other bacteria – such as Mycoplasma
• a urinary tract infection 
• the herpes simplex virus – which can also cause cold sores and genital herpes 
• an adenovirus – which usually causes a sore throat or an eye infection

Non-infectious causes

It is possible for NGU to have a non-infectious cause. This is when something else leads to the urethra becoming inflamed. 

Non-infectious causes of NGU include:

• irritation from a product used in the genital area – such as soap, deodorant or spermicide
• damage to the urethra caused by vigorous sex or masturbation, or by frequently squeezing the urethra – some men may do this if they are worried they have an infection
• damage to the urethra caused by inserting an object into it, such as a catheter – this can be done during an operation in hospital