Sexually Transmitted Infections STI, STD

Authored by , Reviewed by Dr John Cox | Last edited | Certified by The Information Standard

A sexually transmitted infection (STI) is an infection that can be passed from person to person when having sex. You can get an STI by having vaginal sex, anal sex, or oral sex. There are several different types of STI.

The ten most common STIs in the UK are:

There are some other STIs that are uncommon in the UK - for example, donovanosis and chancroid.

Sexually Transmitted Infections

You may not be able to think logically at a time when you most need to. But you will not be alone. Anyone who is sexually active can acquire an STI and there are trained professionals whose job it is to help you.

— Dr Laurence Knott, What to do if you think you have an STI

Editor's note

June 2018 - Dr Hayley Willacy has just read the latest report from Public Health England - see Further reading below. This reports 422,147 new diagnoses of STIs by sexual health services in England in 2017. The most commonly diagnosed STI was chlamydia, which accounted for nearly half of all new STI diagnoses. First-episode genital warts accounted for about 1 in 7 of all new STI diagnoses, while gonorrhoea accounted for about 1 in 9 new diagnoses. Both syphilis and gonorrhoea diagnoses increased, but the number of genital warts cases fell in young women. This is largely because of the high coverage of the HPV vaccination programme for girls of school age.

Several other infections can affect the genital region, so may be mistaken for STIs. Although some of them can be passed on by sexual contact, they can all be caught in other ways. They include:

Symptoms of each STI can vary, from local symptoms affecting the genitals, to symptoms that affect various other parts of the body. The following is not a full list of all possible symptoms. However, these are the common symptoms to look out for:

  • A vaginal discharge.
  • Abnormal vaginal bleeding.
  • A discharge from the penis.
  • A sore, ulcer, rash, or lump that appears on the penis or around the vagina, vulva or back passage (anus).
  • Pain when you have sex.
  • Pain when you pass urine (although the common reason for this is a urine infection and not an STI).
  • Swelling of the glands in your groin.

But remember, in many cases of STI, no symptoms may develop. However, you can still pass on the infection to others even if you have no symptoms. Therefore, if you think that you may have an STI, it is best to get it checked out.

If you have a symptom that you think is due to an STI, or if you have no symptoms but are worried you have caught an STI then you should see a health professional.

How do you find out if you have an STI?

Dr Rosemary Leonard MBE

You can:

  • See your own GP. Your GP can give advice and may examine you. However, if your GP suspects that you may have an STI, in the UK he or she is likely to refer you to a GUM clinic. Some GPs may do tests and manage the situation without a referral to a GUM clinic; or
  • Go to a GUM clinic directly. In the UK you do not need a referral from your GP to go to a GUM clinic. You can ring the local hospital or health authority and ask where the nearest clinic is. Local and national information is also available on the internet - for example, from the .

Until you are checked out, and treated if necessary, you should not have sex. This is to prevent you passing on any infection.

Depending on the initial assessment and examination, the doctor may advise on some tests and ask for your consent to do the tests. Learn more in the leaflet called STI Tests.

If you are diagnosed with an STI then the clinic will encourage you to tell any current or recent sexual partners that you have an infection. You are not obliged to do this or to give out any information about other people. However, it is best that any recent sexual partners should know that they might also be infected. They should be offered testing and treatment if necessary, to prevent the infection being spread any further. This telling of sexual partners is sometimes called contact tracing. If you prefer, clinics can contact people anonymously if you do not wish to tell them yourself. You should be aware that recklessly exposing a sexual partner to the risk of infection is against the law.

The treatment that you will be offered depends on which STI is found. For example, a short course of antibiotics can usually clear away chlamydia, gonorrhoea, syphilis and trichomonas. A cream or lotion can clear pubic lice and scabies. Topical treatments can usually clear most anogenital warts. Treatments for genital herpes, hepatitis B, hepatitis C and HIV are more involved and complex. You will be given advice about what treatment options you have and given time to ask questions.

If you are prescribed antibiotics then it is important to finish the full course of tablets, or else the infection may not be fully cleared. If you develop side-effects then seek advice from the GUM clinic or from your GP as to what to do. Do not simply stop taking the medication. For some infections you will be asked to return after a course of treatment to check that the infection has gone.

Do not have sex again until the time advised by the clinic. Depending on the infection, this may be for a certain length of time after treatment has finished or it may be until you are given the all clear from a repeat test. The aim is to prevent you from passing on the infection to others.

Advice from a sexual health adviser

Most clinics will have a sexual health adviser. You are likely to be seen by the adviser in addition to being seen by a doctor or nurse. A sexual health adviser is specially trained and can:

  • Tell you more about STIs and how to avoid catching them in future. For example, the risk of infection increases with the number of changes of sexual partner. Wearing a condom during sex helps to prevent against STIs.
  • Give you tips on how to cope with any current symptoms.
  • Offer you free condoms which can help to prevent STIs.
  • Give advice about what to tell your sexual partner or previous partners.
  • Help you with contacting previous sexual partners who should be tested or treated. For example, you may be given a card with a number on it, plus a printed message advising the person who is given the card to visit the clinic and to bring the card along. This helps to match them with your notes.

Other services

In addition to diagnosing and treating STIs, if needed, a Genitourinary Medicine (GUM) clinic can also usually:

  • Do a pregnancy test.
  • Arrange counselling if you are pregnant and are not sure what to do.
  • Arrange counselling about the decision to have an HIV test.
  • Provide advice about contraception.
  • Provide emergency contraception.
  • Do a cervical smear test on women if one is due.
  • Diagnose and treat some other conditions of the genitals that are not sexually transmitted. For example, a urine infection, thrush and some skin conditions affecting the genital area.

Further reading and references

  • ; Public Health England, 2016

  • ; Royal College of General Practitioners and British Association for Sexual Health and HIV (Apr 2013)

  • ; British Association of Sexual Health and HIV (2014)

  • ; Public Health England (November 2017)

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