Sexually Transmitted Infections (STIs)

You can't look at someone and tell whether or not they have a sexually transmitted infection (STI). Anyone who has ever had sex or sexual contact with another person could have one, and if they are under 25 the chances are greater.

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What exactly is an STI?

Sexually transmitted infections (used to be called STDs; Sexually Transmitted Diseases) can be passed from person to person through unprotected vaginal, anal or oral sex, by genital contact and through sharing sex toys. You don't need to have lots of sexual partners to get an infection. Having sex or sexual contact once with one person can be enough for an infection to be passed on.

Types of STIs

There are roughly 25 different STIs but we're going to focus on the more common ones amongst young people. There are useful websites at the end if you want to know more.


  • Is the most common STI amongst young women and young men under 25.
  • Most people don't realise they have it because they don't get any symptoms.
  • Can be easily treated with antibiotics.
  • Can cause infertility (unable to have children) in women and men if left untreated.
  • More information about Testing for Chlamydia.
Chlamydia testing

Animal facts:

Koalas are at risk of extinction from chlamydia. Fortunately, it’s much more easily treated among humans. These cuddly characters are now better informed about chlamydia. See why in this video from

Genital Warts

  • Is caused by a virus called HPV (human papilloma virus) which lives in the skin in and around the genital area.
  • The virus can be spread by skin to skin contact so it can be passed on by close genital contact.
  • Are small, fleshy lumps on and around the genital area. However most people will not develop visible warts. This means you may not know whether you or your partner have the virus.
  • Can be removed and there are a variety of treatment methods.
  • Rarely cause any long-term health problems and the virus can clear from the body over time.

Genital Herpes

A wise owl once said you can have herpes for ages and not know. Another wise owl didn’t believe them. Who was right? Watch this video from


  • Is caused by a bacteria, which can live in semen, pre-ejaculate (precum) and vaginal fluids.
  • Often doesn't have any symptoms and so people assume they don't have it.
  • Can be treated with antibiotics. If gonorrhoea is treated early it is unlikely to cause any long term problems.
  • If left untreated can cause infertility (unable to have children) in men and women.


  • There are three types of hepatitis; A, B and C but they are not very common in the UK and you are very unlikely to get Hepatitis C through unprotected sex.
  • Hepatitis A is a virus which causes an infection of the gut that is passed on through infected faeces (poo). It can be passed on through stimulating a partner's anus with your tongue or fingers even if their anal area looks clean.
  • Hepatitis B is a virus, which is present in body fluids such as blood, saliva, semen and vaginal fluid. It can be passed from person to person through unprotected sex.
  • There can be no symptoms, but initial symptoms can be similar to the flu such as temperature, muscle and joint pain and feeling sick.


  • Is a virus that damages the immune system and lives in the blood, semen, pre-ejaculate (precum), vaginal fluids or breast milk of an infected person.
  • Symptoms may not be obvious and at the beginning could feel like having the flu.
  • Has no cure only medication to help you live with the symptoms for the rest of your life.
  • The only way to tell if you have HIV is to have a test. Contact a GUM clinic or sexual health service to talk to someone about HIV and to arrange a test if you are worried. It is better to know than not know,  as you can start medication earlier if you have it, to help you live a long and healthy life.
  • Pre-exposure prophylaxis, or PrEP, is a daily pill that can reduce your risk of HIV if you are HIV negative. PrEP is available for free on the NHS for eligible South West Londoners.

If you are worried that you have been exposed to HIV within the last 72 hours you may be able to access emergency medication (PEP – Post Exposure Prophylaxis) from a GUM clinic, a sexual health clinic or an accident and emergency (A&E) department. The doctor or nurse will ask you some questions and assess whether or not the treatment will be of benefit to you.

To speak to someone in person, call THT Direct on

0808 802 1221

for more information on PEP and where to get it.

Pubic Lice

  • Is caused by a parasite , which can live in the pubic hair, body and chest hair, and facial hair including beards and eyebrows.
  • They have a crab-like appearance so they are often known as crabs.
  • Symptoms including itching in the affected area, sky-blue spots or very tiny specks of blood on the skin, black powdery droppings from the lice in your underwear, and/ or brown eggs on pubic or other body hair.
  • Can be treated with special cream, lotion or shampoo. You do not need to shave off pubic or other body hair.
  • There are no long term health effects.


  • Is caused by a bacteria, which lives in the blood.
  • Symptoms can be difficult to recognise and you might not notice them; however there are three stages of symptoms, with the first being one or more painless sores often around the genitals and the second being a painless rash which can spread all over the body. The third stage only occurs when it is untreated after many years and can cause serious damage to major organs.
  • Can be treated with antibiotics.
  • If left untreated can cause very serious health problems in both men and women and even death, but this is very rare in the UK.

You can get confidential advice and free condoms and contraception from sexual health services near to you.

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