Sexually transmitted infections (STDI) are increasingly common.
Last year, there were nearly half a million new cases of STDs reported from clinics across the UK.
This increase is undoubtedly because more and more people are having active, but sometimes risky, sex lives – often with several partners.
Below you'll find a number of conditions that are currently being seen by genitourinary medicine (GUM) clinics in the UK.
Please bear in mind that some of them (most notably thrush) may not have been acquired through sex.
In 2009, there were almost 216,000 people diagnosed with chlamydia in Britain's GUM clinics. Countless others have acquired the infection, but they do not realise it.
Chlamydia is the most common and fastest-spreading sexually transmitted disease in the UK. It's caused by a bacterium, Chlamydia trachomatis.
Unfortunately, many people (particularly females) have no symptoms at all. Where symptoms do occur, they may include pain in passing urine and a discharge. They usually appear approximately 7 to 21 days after infection.
Chlamydia can also cause a form of conjunctivitis in adults. Also, this eye infection may occur in the newborn babies of mothers who have chlamydia.
In 2009, GUM clinics were seeing about 17,400 new cases of gonorrhoea a year.
Gonorrhoea is caused by Neisseria gonorrhoeae, a bacterium that grows and multiplies quickly in moist, warm areas of the body – such as the cervix, urethra, mouth, or rectum. The cervix is the most common site of infection in women.
However, the disease can also spread to the Fallopian tubes and other internal genital organs, causing such conditions as salpingitis and pelvic inflammatory disease. These may lead to to infertility.
Gonorrhoea is most commonly spread during genital contact, but it can also be passed from the genitals of one partner to the throat of the other during oral sex.
Gonorrhoea of the rectum can occur in people who practice anal sex. In pregnant women, gonorrhoea can be passed from an infected woman to her newborn infant during delivery.
In 2009, over 30,000 new cases of gential herpes were seen at GUM clinics in Britain. In addition, it is believed that some thousands of other people developed herpes but were not seen at a clinic.
Genital herpes is a highly contagious viral condition caused by the herpes simplex virus (HSV).
It infects the skin and mucous membranes of the genitals or rectum, but it can also appear in areas such as the mouth, particularly the lips.
Its chief symptom is an outbreak of small blisters, and these can be very painful.
It's transmitted primarily through physical and sexual contact. During birth, the presence of herpes simplex virus in the birth canal is a threat to the infant's life.
In the last year for which figures are available, there were 6,630 new cases of HIV in NHS clinics. Of these, 4,400 were men and 2,230 were women.
Also, an unknown number of people caught HIV but did not realise it.
The Health Protection Agency estimates that currently there are over 100,000 people in the UK who are HIV-positive, but over 25,000 of them do not know that they have the virus.
Some of those who are HIV-positive will go on to develop AIDS.
AIDS is a potentially lethal disease, which is caused by the HIV virus. HIV means 'human immunodeficiency virus'.
HIV invades and destroys the immune system, which protects the body from infection. This means that a person who carries the HIV virus is prone to many different illnesses and may die from diseases that are harmless to healthy people.
In some countries, particularly those located in Sub-Saharan Africa, the HIV rates are very high. For instance, in the Republic of South Africa it's estimated that about 11 per cent of the population is HIV-positive.
At the present time, British GUM clinics see about 100,000 new cases of genital warts a year. Many other people develop warts, but they are not seen at clinics.
Warts, or condylomata acuminata, are caused by the human papilloma virus (HPV).
Many months can pass from the time of infection to the actual development of warts, so it may be very difficult to determine who you got them from.
In women, HPV can lead to microscopic changes in the cervix and to the development of cervical cancer.
HPV is now thought to be associated with various other cancers, including carcinoma of the anus and possibly of the throat and adjoining regions.
In 2009, there were 3,273 cases of syphilis seem at UK GUM clinics.
If left untreated, syphilis is a dangerous and life-threatening disease. It's caused by a corkscrew-shaped germ called Treponema pallidum.
It's passed on by intercourse or by almost any other form of sexual interaction.
The first symptom appears between 9 and 90 days after exposure to the germ that causes it. A small lump develops at the infection site, and this soon breaks down to form a painless ulcer.
Later, there is a secondary stage (characterised by fever, rashes and throat ulcers), and eventually a tertiary stage (in which the germ may attack the brain, spinal cord and other organs).
Trichomonas vaginalis (often known as 'TV') is a protozoan 'bug' that affects the vagina.
It causes a green or yellowish, bubbly vaginal discharge and intense vulval soreness. It also produces a 'fishy' smell.
However, some women have no symptoms at all, and men rarely do.
For unknown reasons, the incidence of 'TV' in the UK has declined sharply in recent years, though it is reported as still being common in the USA. Only about 6,000 cases were diagnosed in UK clinics last year. In addition, a substantial number were treated by GPs.
The diagnosis of bacterial vaginosis (BV) has become common during the last 10 years, with about 97,000 women per year being seen in GUM clinics, and an unknown number being treated elsewhere.
BV is a common cause of vaginal discharge. The discharge is usually whitish or greyish or sometimes yellowish, and tends to have an off-putting ‘fishy’ odour.
Unlike the discharges caused by thrush or trichomonas, it’s not usually associated with soreness, discomfort or itching.
It's uncertain if BV is transmitted sexually, especially as there's no equivalent condition in males.
Thrush is one of the commonest of all 'female infections'.
It's impossible to say precisely how common it is, since it's not only treated in GUM clinics but also in GPs' surgeries and Family Planning clinics.
Furthermore, huge numbers of women simply treat it themselves, since anti-thrush treatment is available without prescription in every pharmacy in Britain. At a conservative estimate, there must be at least half a million thrush infections per year in Britain.
Candida is a fungal infection. It loves warm, moist conditions, which is why it flourishes in women's vaginas – and also in babies' mouths, particularly in the newborn.