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Sexually transmitted infections (STIs)

Sexually transmitted infections (STIs) pass from person to person during sexual activity. You can catch an STI if you have unprotected vaginal, anal or oral sex or share sex toys with someone who already has the infection.

If you think you have an STI, it’s important to speak to your GP or visit a sexual health or genito-urinary medicine (GUM) clinic as soon as possible. Diagnosing and treating STIs in their early stages may reduce your risk of developing complications.

STIs are most common in people under 25, but anyone who’s sexually active is at risk. STIs can be caused by bacteria, viruses, fungi or parasites. Chlamydia and genital warts are the most common STIs in the UK.

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  • Symptoms Symptoms of sexually transmitted infections

    STI symptoms vary from person to person and depend on which STI you have, although you may not have any symptoms at all. You may notice:

    • unusual discharge from your vagina, penis or anus – the discharge may thicker than usual, coloured or smelly
    • stinging, pain or burning when you pass urine
    • itching, rashes, lumps, sores or blisters around your genitals (your vagina or penis) or anus
    • stinging, burning, pain and/or vaginal bleeding during or after sex
    • bleeding between your periods
    • pain or swelling of your testicles and/or epididymis (this is the tube that runs down the back of each testicle)
    • pain in your lower abdomen (tummy)

    Even if you don’t have any symptoms, you can still pass the infection to someone else. So it's important to get yourself tested if you think you may have an STI. Some STIs can lead to more serious health problems, such as infertility, if they aren’t treated.

  • Diagnosis Diagnosis of sexually transmitted infections

    If you think you have an STI, go to a sexual health or genito-urinary medicine (GUM) clinic. You don’t have to ask your GP to refer you to a GUM clinic – you can make your own appointment. If for any reason you can’t go to a sexual health clinic, call your GP for advice.

    It’s best to go to a GUM clinic because the doctors and nurses there specialise in diagnosing and treating STIs and can help to anonymously trace previous sexual contacts.

    All visits to a GUM clinic are confidential and you don't have to give your real name. Your details won't be sent to your GP unless you confirm in advance that you’re happy for the clinic to do this.

    Your doctor or nurse will usually ask about your medical history and whether you’ve had similar symptoms or an STI before. You may also be asked about your current and recent sexual partners and what type of contraception you use.

    Your doctor or nurse will usually need to examine you to look for any signs of infection. For women, this may involve an internal examination (looking at your vagina and cervix). Other tests for STIs include swabs (these are samples taken with a small, round cotton bud), and blood and urine tests. The tests shouldn’t be painful, but you may feel some discomfort if you have a swab or internal examination.

    If you're diagnosed with an STI, it's important to contact your previous sexual partners so that they can be tested too. GUM clinics can send anonymous notifications on your behalf if you're willing to provide details.

  • Causes Causes of sexually transmitted infections

    STIs are caused by bacteria, viruses, fungi or parasites. You can catch these infections during sex, genital contact, sharing sex toys and oral sex with an infected person. Drug users can catch blood-borne viruses through sharing contaminated needles and injecting equipment. Some of these viruses are also transmitted sexually.

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  • Prevention Prevention of sexually transmitted infections

    You can reduce your risk of catching an STI by taking certain precautions, such as practising safer sex. Safer sex methods include using condoms for vaginal, anal and oral sex. This can help prevent the spread of HIV and reduce the risk of many other STIs.

    You may be able to be vaccinated against some STIs, such as hepatitis B, if you’re at a high risk of catching them.

    Before having sex with a new partner, get yourself tested for STIs and suggest that they do this too.

    If you’ve been diagnosed with an STI, it's important to wait until you have been given the 'all clear' before you have sex again.

  • Chlamydia Chlamydia

    Chlamydia is the most common bacterial STI in the UK. It’s particularly common in people under 25. The National Chlamydia Screening Programme recommends that all 15- to 24-year-olds in England should be tested every year if they’re sexually active.

    Chlamydia infects your cervix (the neck of your uterus) or urethra (the tube that carries urine from your bladder and out through your penis or vulva). The infection may then spread to other parts of your body, such as your uterus and tubes.

    Around seven in 10 women and half of men infected with chlamydia don’t have any signs or symptoms.

    When symptoms do occur in women, these include:

    • bleeding between your periods or heavier periods
    • pain and/or bleeding during or after sex
    • pain in your lower abdomen (tummy)
    • a cloudy, yellow discharge from your cervix
    • pain when you pass urine

    Possible symptoms in men include:

    • a white, cloudy or watery discharge from your penis
    • pain when you pass urine
    • pain in your testicles

    If you have a chlamydia infection in your rectum, you’re unlikely to have symptoms there. But sometimes you may notice some pain and an unusual discharge from your anus.

    Chlamydia can be treated with antibiotics. If your doctor suspects you have chlamydia, they may start treating you before your test results are back. If chlamydia isn’t treated, it can lead to more serious problems, such as infertility.

  • Genital warts Genital warts

    Genital warts are the most common viral STI in the UK. They are caused by the human papilloma virus (HPV). In the UK, all girls aged 12 and 13 are offered the HPV vaccine, as part of the National HPV Vaccination Programme. The vaccine protects against the types of HPV that cause cervical cancer, but one brand of the vaccine also protects against some strains of the virus that cause warts.

    Genital warts can develop on any part of your penis, vagina or anus. They may be small, smooth, round bumps, larger growths that are grouped together or small cauliflower-shaped bumps. The warts don’t always cause symptoms, but are sometimes painful, burning or itchy. It can take a few weeks or months after you first come into contact with the virus for the warts to appear.

    Once you’ve been infected, you can pass the HPV virus to other people, even if you don’t have any genital warts at the time. Using a condom reduces your risk of passing on the virus but won’t fully protect you or your partner.

    Genital warts often disappear on their own, so your doctor may suggest that you don’t treat them. He or she will help you decide whether or not to treat them. The advice will be based on where your warts are, how much they are affecting you and whether you have any other medical conditions.

    If you decide to treat the warts, your doctor may use chemical products or liquid nitrogen (cryotherapy), but neither of these is guaranteed to be successful. The affected area may be red and sore for a while after the treatment. You may need to have several treatments to get rid of the warts for good.

    You may also be able to have the warts removed by laser treatment or surgery.

  • Genital herpes Genital herpes

    Genital herpes is caused by the herpes simplex virus type-2 (HSV-2). Many people infected by this virus don’t have any symptoms.

    If you do have symptoms, you may first notice burning or tingling in your vagina, penis or anus. Later on, you may develop fluid-filled blisters or sores on the skin on or around your vagina, cervix or penis. If you’ve had oral sex, then you may have sores around your mouth. You may also feel generally unwell, tired or have a high temperature (fever). It may also be painful when you pass urine.

    This first (primary) outbreak of genital herpes can last up to four weeks if it isn’t treated. You may then have further bouts in the following months, but these tend not to last as long or be as severe.

    Another type of herpes simplex virus, HSV-1, usually causes oral herpes (cold sores). But both viruses can affect your mouth or genitals. So if you’re infected with the HSV-1 virus, you can pass it to your partner’s genitals during oral sex. Oral sex can also pass the virus to your mouth.

    If you have genital herpes but don’t have any symptoms, you can still pass the virus on to your partner. Using condoms can reduce the chance of passing the virus on, but won’t provide complete protection.

    No treatment can completely remove the herpes simplex virus from your body. Once you catch the virus, you have it for life, but you should have fewer flare-ups as time goes on. For most people, the flare-ups do eventually stop completely. When you have a flare-up, your doctor can prescribe antiviral medicines to help clear up your blisters more quickly. You may be able to ease any pain by having lukewarm baths and taking painkillers. If you have frequent attacks, your doctor may prescribe daily antiviral medication to prevent these attacks.

  • Gonorrhoea Gonorrhoea

    Gonorrhoea is caused by bacteria that can infect your urethra, cervix, rectum, throat and eyes. Around one in 10 men and half of all women who are infected with gonorrhoea don’t have any symptoms. And if you do get symptoms, it can take up to 14 days after you are infected for them to appear.

    In women, symptoms may include:

    • thin, slightly smelly vaginal discharge
    • pain when you pass urine
    • mild lower abdominal (tummy) pain or tenderness
    • bleeding between your periods
    • pain during sex

    In men, symptoms may include:

    • yellow or green discharge from the tip of your penis
    • pain when you pass urine
    • pain or tenderness in your epididymis (the tube that runs down the back of each testicle) – this is usually just on one side

    If the infection is in your rectum, you won’t usually have any symptoms, but it can sometimes cause anal itching, bleeding or discharge. Gonorrhoea infection caused by oral sex can occasionally cause a sore throat.

    It’s important that you’re treated for gonorrhoea as soon as possible. If not, the infection can cause serious long-term health problems including infertility and some types of arthritis. Gonorrhoea can be treated with antibiotics.

  • Hepatitis B Hepatitis B

    Hepatitis B is an infection of your liver. It’s caused by the hepatitis B virus. Around half of people with hepatitis B will develop symptoms. These can begin any time from six weeks to six months after you’re infected.

    The symptoms can include:

    • feeling generally unwell, similar to having flu
    • losing weight
    • feeling sick or vomiting
    • aching in the top right of your abdomen (tummy)
    • yellowing of your skin and eyes (jaundice)
    • itchy skin
    • darker urine and lighter-coloured faeces

    Most people with hepatitis B get better without any treatment. You can generally treat your symptoms by drinking lots of fluids, resting and taking anti-sickness medicines. Itching can be difficult to treat, but you may find simple measures, such as wearing loose clothing and not having hot baths or showers, help.

    If the infection hasn’t cleared from the body in six months, this is known as chronic (long-term) hepatitis. This is more likely if you have a weak immune system; for example, because you’re taking certain medicines. Many people with chronic hepatitis don’t have any symptoms, but some can still pass the infection on to other people.

    If you have chronic hepatitis, you’ll be at a higher risk of developing cirrhosis of the liver and liver cancer. If you have cirrhosis of the liver, your normal liver tissue is replaced with scar tissue (called fibrosis). You’ll be referred to a doctor who specialises in the treatment of chronic hepatitis. You may be prescribed antiviral or other medicines that help your body to clear the infection.

    If you’re at a high risk of catching hepatitis B, you can be vaccinated against the infection. People who are considered to be high risk include those who are HIV positive, men who have sex with men, health care workers, and travellers to certain countries.

    If you think you’ve been exposed to hepatitis B and haven’t been vaccinated, go to a sexual health clinic as soon as possible. You can have an injection of the vaccine and in some cases a protective injection (hepatitis B immunoglobulin). This works best if you’re given it within 48 hours of exposure.


    Human immunodeficiency virus (HIV) infection affects your immune system. Some people infected with HIV have no signs and symptoms at all. But you may develop flu-like symptoms up to six weeks after becoming infected. Your symptoms may include a high temperature, aches and pains, a sore throat, headaches and swollen glands. Over time, the HIV virus may weaken your immune system, putting you at risk of other infections and tumours.

    Current treatments can’t get rid of HIV from your body completely, but they are effective at controlling the virus and keeping you healthy. You can take a combination of medicines called antiretrovirals to reduce the levels of HIV in your blood, and improve your immune system. Treatment can effectively reduce your risk of developing serious health complications due to HIV and keep you well.

    Some people may still pass on the infection through unprotected sex even if they’re taking antiretroviral medicines for HIV. So it’s important to practise safe sex by always using a condom.

    If you’ve had unprotected sex with someone who has HIV or is at high risk of HIV, visit a sexual health clinic or Accident and Emergency. You can take a course of antiretroviral medicines straight away (called post-exposure prophylaxis) to reduce your risk of becoming infected. To be effective, you need to start these medicines within 72 hours of exposure to HIV and take them for 28 days.

  • Pubic lice Pubic lice

    Pubic lice are tiny insects that live in coarse body hair, such as pubic hair, chest hair, eyelashes and eyebrows. They are not the same as head lice. They are sometimes called ‘crabs’.

    The lice are very tiny and hard to see, but you may find them if you use a fine-toothed comb. You may notice itchy red spots on your skin or brown eggs (nits) stuck to your body hair. You may see brown-black powdery spots in your underwear from the lice droppings. Pubic lice may make you feel itchy.

    You can treat a pubic lice infection with insecticide lotions or shampoos. You need to use these over your whole body and leave them on for up to 12 hours. You may need to repeat the treatment seven days later.

  • Syphilis Syphilis

    Syphilis is a bacterial infection. It’s uncommon in the UK compared with some other STIs, such as chlamydia and genital warts, but numbers are increasing. The disease has three stages: primary, secondary and tertiary.

    The primary stage begins any time between nine and 90 days after you’re infected with the syphilis bacteria. You may notice that one or more sores appear on your skin. The sores can appear anywhere on your body, but will usually affect your penis, anus, vagina, cervix, rectum, mouth or lips. The sores usually heal within three to 12 weeks.

    The secondary stage begins a few weeks after your sores have healed. You may feel generally unwell with flu-like symptoms and a rash.

    If you’re not treated for syphilis, after a number of years you can develop the tertiary stage of the disease. This can cause serious health problems, affecting many parts of your body including your nervous system and heart.

    Syphilis can be treated with antibiotics.

  • I'm too embarrassed to go to a sexual health clinic. Are there home-testing kits available? I'm too embarrassed to go to a sexual health clinic. Are there home-testing kits available?


    You can buy home-testing kits for some STIs, but these aren’t always reliable or accurate. Because of this, although self-testing kits can be useful, it’s better to get checked out by a doctor as well. If you go to a sexual health or genito-urinary medicine (GUM) clinic, you can be treated quickly and they can also give you advice about preventing future STIs.

    More information

    Sexual health or GUM clinics offer free and confidential testing for STIs and advice about preventing them. You may feel embarrassed about going to a clinic, but the people who work there are used to dealing with this. Your tests will be kept confidential and you don’t have to give your real name. STIs can have serious health implications, so it’s important to have an accurate test.

    You can buy a chlamydia test to do at home and the first legally approved HIV self-testing kit is also now available in the UK. Keep in mind that how accurate these tests are varies. Only buy them from reputable sources, ideally with advice from a GP or other healthcare professional. Make sure the kit carries a CE mark and that the packaging is intact. Always follow exactly the instructions on how to use the kit.

    Remember that no test can be completely reliable. If you’re worried about any STI or unusual symptoms, visit a GUM clinic or contact your GP.

    If you’re under 25, you can get a free and confidential chlamydia test as part of the National Chlamydia Screening Programme. You can do the test yourself and don’t need to be examined. If you don’t want to visit a sexual health clinic, you can get the test at many other places, including youth clubs, colleges and some pharmacies.

  • Should I get treatment for an STI if I’m pregnant? Should I get treatment for an STI if I’m pregnant?


    Yes, it’s important that you go to a sexual health or GUM clinic or contact your GP. You can pass some STIs on to your baby before, during or after birth. You may need to be treated for the infection during pregnancy in order to protect you and your baby from serious health problems.

    More information

    If you’re diagnosed with an STI while you’re pregnant, your treatment will vary depending on the specific infection. This often depends on how many weeks pregnant you are because not all treatments are suitable during all stages of pregnancy. Most bacterial STIs can be treated with certain antibiotics that are safe to take during pregnancy. Viral STIs can be more difficult to treat but there are ways that the risk of passing the infection on to your baby can be reduced.

    If you’re not treated for an STI before or during pregnancy, your baby’s health could be seriously affected. Some STIs can mean your baby is born early or has a low birth weight. Sometimes, STIs can lead to a miscarriage late in pregnancy.

    Your baby may need treatment when they’re born to help prevent complications of STIs. Sometimes, you may be offered a caesarean delivery to help prevent your baby becoming infected during childbirth. HIV can be passed to babies through breastfeeding, so women in the UK who are HIV positive are advised to use formula milk instead.

    Speak to your GP or midwife about the best way to protect you and your baby if you’ve been diagnosed with an STI.

  • Someone I had sex with has an STI but I don't have any symptoms. Should I still get tested? Someone I had sex with has an STI but I don't have any symptoms. Should I still get tested?


    Yes, it’s a good idea to get tested. You don’t always have symptoms if you have a STI and if left untreated, it could lead to serious health complications.

    More information

    Sometimes you may not know that you have an STI because you don’t have any symptoms. But if you think you may have put yourself at risk of catching an infection (such as through unprotected sex), it's important to get tested. Go to a sexual health or genito-urinary medicine (GUM) clinic.

    If you do have an infection but don’t treat it, it may get worse. This can lead to complications. You could also pass it on to someone else.

    Using a condom every time you have sex can reduce the risk of getting an STI. But not all STIs can be prevented in this way.

    If you would like further confidential advice, there are helplines you can ring to get more information.

  • Other helpful websites Other helpful websites

    Further information


    • Overview of sexually transmitted infections. BMJ Best Practice., published 19 January 2015
    • A BASHH guide to safer sex. British Association for Sexual Health and HIV., published January 2012
    • Sexually transmitted infections. PatientPlus., reviewed 7 June 2013
    • Chlamydia genital infection. PatientPlus., reviewed 12 August 2013
    • Anogenital warts. PatientPlus., reviewed 29 June 2015
    • Gonorrhoea infection. BMJ Best Practice., published 25 April 2014
    • Syphilis. BMJ Best Practice., published 20 February 2015
    • Lazaro, N. Sexually transmitted infections in primary care 2013. Royal College of General Practitioners/British Association for Sexual Health and HIV., accessed 1 September 2015
    • Standards for the management of sexually transmitted infections. British Association for Sexual Health and HIV., published January 2015
    • Sexual health and contraception. Oxford handbook of general practice. Oxford Medicine Online., published April 2014
    • BASHH CEG 2015 summary guidance on tests for sexually transmitted infections. British Association for Sexual Health and HIV., published April 2015
    • Genitourinary history and examination (female). PatientPlus., reviewed 20 June 2014
    • Hepatitis B. BMJ Best Practice., published 26 January 2015
    • Infection report Volume 9 Number 22. Sexually transmitted infections and chlamydia screening in England, 2014. Public Health England., published 23 June 2015
    • Genital tract chlamydia infection. BMJ Best Practice., published 18 August 2015
    • Chlamydia – uncomplicated genital. Clinical Knowledge Summaries., published May 2009
    • Your guide to the HPV vaccination from September 2014. Gov UK., accessed 1 September 2015
    • Genital warts. BMJ Best Practice., published 7 May 2015
    • Genital warts. The Merck Manuals., published September 2013
    • Herpes simplex infection. BMJ Best Practice., published 6 March 2015
    • Herpes simplex genital. PatientPlus., reviewed 16 October 2012
    • Gonorrhea. The Merck Manuals., published September 2013
    • Gonorrhoea. PatientPlus., reviewed 25 September 2014
    • Gonorrhea. Medscape., published 26 June 2015
    • Hepatitis B. PatientPlus., reviewed 2 August 2013
    • Cirrhosis. PatientPlus., reviewed 5 June 2015
    • HIV infection. BMJ Best Practice., published 18 August 2015
    • Human immunodeficiency virus. PatientPlus., reviewed 4 April 2015
    • Pubic and body lice. PatientPlus., reviewed 18 October 2013
    • Syphilis. The Merck Manuals., published September 2013
    • Advice about buying self-test kits for sexually transmitted diseases (STDs). Medicines and Healthcare Regulatory Agency (MHRA)., published October 2012
    • Sexually transmitted infections. Chlamydia. Family Planning Association., accessed 3 September 2015
    • First home HIV self-testing kit goes on sale in the UK. The Pharmaceutical Journal., published April 2015
    • National chlamydia screening programme. Public Health England, 2013.
    • Managing sexually transmitted infections in pregnant women. Medscape., published 2012
    • Foley E, Clarke E, Beckett VA, et al. Management of genital herpes in pregnancy. RCOG/BASHH., published October 2014
    • British HIV Association guidelines for the management of HIV infection in pregnant women 2012 (updated May 2014). British HIV Association. HIV Medicine 2014; 15 (Suppl. 4):1–77.
    • Infectious syphilis and congenital syphilis: recent epidemiology. Gov UK., published 1 November 2013
    • The immune system and cancer. Cancer Research UK., published 29 October 2014
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