Chlamydia is the most common bacterial STI. It’s caused by bacteria called chlamydia trachomatis. The bacteria live in the semen and vaginal fluids of infected people. If it goes untreated and causes pelvic inflammatory disease (PID), it can lead to infertility.

The most common symptom is no symptom at all. This means it can be passed on without knowing. Symptoms can appear differently depending on your sex.

Female symptoms:

• Abdominal (tummy) pain
• Back pain
• Pain when urinating (weeing)
• Unusual vaginal discharge
• Bleeding between periods
• Pain during sex
• Bleeding after sex.

Male symptoms:

• Discharge from penis
• Burning sensation when urinating (weeing)
• Swollen and sore testicles
• Itchy and burning penis.

Treatment

Chlamydia is easily treated with antibiotics. You will always be offered treatment if your partner tests positive for chlamydia. You can catch chlamydia more than once, even if you’ve been treated for it before.

Learn more about chlamydia

Gonorrhoea is a bacterial infection. It is caused by a bacteria called gonococcus or neisseria gonorrhoeae. It is found in the semen and vaginal fluids of infected people. This bacteria can live in cells in the body. These cells can be in the entrance of the womb (cervix), the tube that urine passes through (urethra), the end of the large intestine (rectum) and the throat. Like chlamydia, it can lead to infertility if untreated.

Symptoms

Symptoms of gonorrhoea usually develop within a couple of weeks of infection. Some people get symptoms months later. Half of women with gonorrhoea have no symptoms. 1 in 10 men with gonorrhoea also have no symptoms. This means it can be passed on without knowing. Symptoms can appear differently depending on your sex.

Female symptoms:

• Smelly vaginal discharge that is yellow or green, or thin and white coloured.
• Abdominal (tummy) pain.
• Burning feeling when urinating (weeing).
• Needing to wee more often.
• Heavier periods and bleeding between periods.

Male symptoms:

• Penis discharge.
• Burning feeling when urinating (weeing).
• Needing to wee more often.
• Painful or sore testicles.
• Sore, red foreskin.

Treatment

Gonorrhoea is easily treated with antibiotics. You will need to have another test after treatment to make sure it has worked. You will always be offered treatment if your partner tests positive for gonorrhoea. You can catch gonorrhoea more than once, even if you’ve been treated for it before.

Learn more about gonorrhoea

Human Immunodeficiency Virus (HIV) is a virus that weakens the body’s immune system. If HIV weakens the immune system so much it can’t fight infections, this is known as AIDS (Acquired Immune Deficiency Syndrome). With early diagnosis and treatment, most people with HIV will not develop AIDS. In the UK, doctors call AIDS ‘late-stage HIV’ or ‘advanced HIV.’

The virus can be passed on through bodily fluids of an infected person. This includes blood, semen (including pre-cum) and vaginal fluids. HIV is not spread through saliva (spit), tears, urine (wee), faeces (poo), nasal mucus (snot) or sweat. HIV is spread by:

• Unprotected sex – anal, vaginal and sometimes oral.
• Sharing sex toys
• Infected blood – e.g., blood transfusions or sharing injecting equipment.
• HIV positive mother to child – during birth and through breastfeeding.

Symptoms

Most people with HIV will experience a short, flu-like illness. This can cause a sore throat, fever, tiredness, aching joints, swollen glands and a rash a couple of weeks after getting the virus. These are signs that the immune system is responding to the virus and developing antibodies. HIV tests take a small sample of blood to look for these antibodies.

Following this flu-like illness many people remain symptom free for years. They may look and feel well. Some people may not experience the flu-like illness at all. If untreated, the virus will multiply. Over time it attacks a person’s immune system and causes immune system damage. This means that the body cannot fight other infections or diseases.

Symptoms of a weak immune system include:

• Weight loss
• Diarrhoea that lasts longer than a week
• Night sweats
• Recurring infections
• Serious life-threatening illnesses.

Treatment

HIV cannot be cured, but symptoms can be treated. HIV is treated with anti-retroviral drugs during Antiretroviral Therapy (ART). The drugs stop the virus multiplying. This gives the immune system chance to repair itself.

If you think you have been exposed to HIV it is important to be tested – even if you don’t have symptoms. Any delay could allow the virus to damage your immune system. Starting treatment early is important.

Emergency treatment

If you have been exposed to HIV in the last 72 hours (three days) it’s possible to take anti-HIV medication. This medication is called PEPSE (post-exposure prophylaxis after sexual exposure). PEP is a 28-day treatment that it may stop you becoming infected. We do not provide these treatments and advise you contact your local sexual health services for advice and support.

Prevention

If your partner has HIV and you do not, you may be able to take prevention medication to lower your risk. This medication is called pre-exposure prophylaxis (PrEP). PrEP is for HIV-negative people to reduce their risk of infection. PrEP is available in England at sexual health clinics.

Learn more about HIV

Syphilis is a bacterial infection. It can cause serious problems if untreated. It’s important to get tested and treatment as soon as possible if you think you may be at risk.

Symptoms

The symptoms of syphilis are often mild and difficult to recognise. This means it can be passed on without knowing. Some people with syphilis have no symptoms.

Symptoms include:

• Small, painless ulcers or sores on the penis, vagina, around the anus or mouth.
• Red, blotchy rash typically on the palms of the hands or soles of the feet.
• Small skin growths (similar to genital warts) on the vulva or anus.
• White patches in the mouth.
• Tiredness
• Headaches.
• Joint pains
• High temperature (fever).
• Swollen glands in your neck, groin or armpits.

Treatment

Syphilis is usually treated with a short course of antibiotics. You can catch syphilis more than once, even if you’ve been treated for it before.

Learn more about syphilis