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In short, determining for certain whether you or your partner has a sexually transmitted infection is impossible without having an STI test.

You can have an STI without any outward symptoms for long periods, and pass it on to others without realising, potentially causing serious health complications.

Some STIs can be transmitted not only by penetrative sex, but also by genital or bodily contact.

We have listed some of the obviously recognisable signs of common STIs here, but we will also discuss how you can find out if you or your partner has an STI which has yet to show symptoms, and provide some guidance on how to avoid contracting STIs in future.


The most common STI in Great Britain, this bacterial infection can be transmitted by unprotected sex or genital contact. Around 200,000 people in England were diagnosed with the disease in 2015.

The NHS recommends that if you are under 25 and sexually active, you should be tested annually or every time you change your sexual partner.

People with chlamydia often don’t get any noticeable symptoms at all. If you do, they can take weeks or months to appear, and may seem to disappear after a short while.

You can still infect others even if you don’t show any symptoms.

  • In women, symptoms can include vaginal discharge, bleeding after sex, heavy periods, and abdominal pain.
  • Men may experience genital discharge, an itching sensation in the urethra or pain in the testicles.
  • Both sexes may have discomfort while urinating.

The vast majority of chlamydia cases can be cured with antibiotics if caught early. If left untreated it can cause more serious complications, including problems with pregnancy in women and fertility in both sexes.


This bacterial infection is becoming a cause of increasing concern, as a strain of the disease which has become resistant to antibiotics is spreading across the UK and Europe. It is the second most common STI in the UK, with 40,000 cases reported in England alone in 2015.

It can be transmitted through unprotected penetrative and oral sex. Around half of women and one in ten men will not be aware of any symptoms, and you can still pass gonorrhoea on to someone else when it is asymptomatic.

  • Men with symptoms might notice a yellow, white or even green discharge, an inflamed or swollen foreskin and soreness when urinating or ejaculating.
  • Women may feel uncomfortable when passing water, have a yellow or green vaginal discharge, or less commonly, abdominal pain, vaginal bleeding or heavy periods.
  • As gonorrhoea can be contracted through anal and oral sex, your throat and rectum can also become infected. While you won’t show symptoms in your mouth, you may experience pain, itching, discharge and mild diarrhoea.

If you get seminal or vaginal fluid from someone with gonorrhoea into your eyes, you may become susceptible to developing conjunctivitis.

Gonorrhoea can still be cured with antibiotics. Previously, it was treated with single drug courses. However, the development of resistant strains means that now the infection will requires two types of antibiotic drug to effectively clear it. The first line in the UK is an antibiotic injection given in conjunction with a tablet.

If gonorrhoea is not treated it can potentially cause issues with fertility in both women and men:

Women may have complications during pregnancy including premature birth and even miscarriage. It can also lead to conjunctivitis in newborn babies that will require antibiotic treatment to prevent permanent vision damage.

Men risk developing Chordee in the long term, a condition where the tip of the penis begins to bend either downwards or upwards. This makes erections painful and may require surgery.

Blood poisoning has been reported in rare cases.


Transmitted by having vaginal, oral or anal sex (and in rare cases by physical contact), this bacterial infection can again be passed on even if you do not show any symptoms yourself.

If left untreated for a long time it can become very serious, potentially leading to strokes, heart conditions, brain damage, loss of hearing or vision and meningitis. It affects men and women, but male cases appear much more commonly in gay and bisexual men.

  • The early signs of syphilis (known as ‘primary syphilis’) are one or more painless ulcers on or near the penis or vagina, or another area of sexual contact such as the mouth or bottom. Those infected might also develop swollen glands close to these ulcers or under your arms.
  • The signifiers of ‘secondary syphilis’ are a flu-like illness, headache, sore throat and a skin rash. In time, these may clear up, but the infected person will still remain infectious and are likely to develop some of the acute health problems discussed above.
  • The final stage (tertiary syphilis) can take several years to manifest itself, leading to the severe health complications listed above.

Syphilis can be treated with antibiotics, which may require administration intravenously in cases where someone has had it for a long time. While it can even be completely cured in its later stages, any health conditions the disease has caused may not be.


The human immunodeficiency virus can be spread by unprotected vaginal or anal sex, as well as from infected blood. There is still no cure for HIV.

While for many years it was the cause of the fatal acquired immune deficiency syndrome (AIDS), developments in medical science mean that someone with HIV can live a long, healthy life with proper medication and health management.

As the name suggests, HIV attacks the body’s immune system, damaging its ability to combat infection and disease. If not treated, someone with the infection may develop AIDS, which can lead to conditions like pneumonia and tuberculosis becoming fatal.

People with HIV can live normally for many years without knowing it, but they are capable of infecting sexual partners without showing any symptoms.

HIV can affect men and women, gay and straight. 6,000 people were diagnosed in the United Kingdom in 2013, with over 100,000 people in total living with with the disease. It is thought that around a quarter of people with HIV do not know that they have the condition.

  • In the majority of cases, in the weeks following infection someone might notice symptoms similar to those of flu (headache, fatigue, sore throat, fever); this reaction is called seroconversion.
  • Someone with the infection may also feel generally ‘run down’ with joint and muscle pains or mouth ulcers. This usually lasts a week or two, and as these are not commonly attributed to HIV, it is easy for people to not realise they have been infected.

After this the infection enters a long period of dormancy sometimes lasting several years, when an infected person may not experience any symptoms. However, eventually the immune system will reach a point where it finds it difficult to fight common infections and someone with the infection will start noticing more serious signs, such as weight loss, acute diarrhoea and normally curable medical conditions that become chronic.

After a positive diagnosis, a doctor will decide whether to start treatment dependent upon the level of the virus in the bloodstream by measuring what is known as the CD4 count. CD4 is a type of blood cell responsible for helping the body to combat infections.

Once someone’s CD4 count falls below a certain level (usually 350 for those with no underlying health conditions), they will start treatment, and need to take medication for the rest of their life.

Genital warts

It’s possible to have the HPV virus without having genital warts. While the condition is more infectious where warts are present, it can still be transmitted even if there are none.

  • These warts on or near the penis, vagina or anus are caused by the human papilloma virus (HPV). Warts can also develop on the thighs or in concealed areas, such as inside the rectum. They can be transmitted via intimate bodily contact as well as unprotected penetrative or oral sex.
  • The size of these warts can vary and they may be uncomfortable, depending on where they are.

Warts can be treated in a number of ways dependent on the type of wart. In some cases a prescription cream or liquid is issued (known as a topical treatment); and in others, treatments termed as physical ablation are required, where the wart is frozen off, cut out, or removed by laser.

The topical treatments can take quite some time to be effective, and the patient will need to refrain from sexual contact so they do not infect anyone else.

Genital Herpes

It’s easy not to notice a herpes outbreak, so you can pass it on to your partner even if you think you are not showing any symptoms.

  • Engendered by the herpes simplex virus (HSV), the main symptoms of this condition are sore, itchy, blistered areas of skin which appear on or near the genitals, as well as on your thighs and bottom.
  • People can also experience flu-type symptoms. You can catch herpes from intimate body contact, as well as sex. You can also spread genital herpes to the mouth by kissing.

While a flare-up of genital herpes can be treated with a course of antiviral medication, there is currently no cure, so even if the symptoms clear up the virus stays in your system. Recurrent outbreaks gradually become less severe.

If you have more than six outbreaks a year, you are advised to see your doctor who may be able to manage your condition with a long term course of treatment.

It’s important that if you notice the symptoms of an outbreak that you avoid sexual contact altogether, as condoms are not completely effective in preventing transmission.

You can read more about the factors that trigger reactivations and how to administer treatment on our information pages.


This type of infection is not as easy to detect as other STIs, as its symptoms are often mistaken for other conditions. Trichomoniasis is caused by trichomonas vaginalis, a parasite that infects the genitals and urethra, but may also infect the prostate gland and the head of the penis in some male cases.

It is transmitted via unprotected vaginal sex, and can be symptomless in up to half of people with the infection.

  • Women with symptoms may notice an unnaturally green or yellow coloured vaginal discharge with a strong odour, and itchiness, swelling and discomfort near the vagina.
  • Men may also notice a discharge which is white in colour or inflammation of the foreskin or head of the penis.
  • Both sexes might experience pain during sexual activity or when passing water.

Trichomoniasis can be treated with a short course of antibiotics. While this condition has occasionally been known to clear up by itself, this is by no means a certainty, and not getting treated puts your partner at risk of infection.

Getting tested

If a person is sexually active, the only way to be certain that anyone is free of STIs is to be tested regularly.

You can find sexual health or GUM clinics in most towns and many operate drop in sessions where you don’t need to make an appointment. They are completely confidential, and as well as being tested, you can get free advice and often free condoms.

You will probably be asked about your recent sexual history; it is important that you are as honest as possible so they are aware of the risks of infection which are applicable in your case.

STI test kits are now also available to buy online. Some of these enable you to collect a small sample of urine or blood, and send this off to a lab for analysis. When you use services such as ours, your result will then be sent to your patient area once ready, so you can login and view it.

Other test kits you can buy online don’t need to go to a lab, and can give you a result at home in minutes.

If you've been tested and found to have contracted an STI, the treatment you are issued will depend on the nature of your infection.

Page last reviewed:  13/12/2019