Sexually transmitted infections (STIs) are passed from one person to another through unprotected sex or genital contact.
This page provides an overview of the different STIs and links to more information about these conditions.
Chlamydia is the most common STI in the UK and is easily passed on during sex. Most people don't experience any symptoms, so they are unaware they're infected.
In women, chlamydia can cause pain or a burning sensation when urinating, a vaginal discharge, pain in the lower abdomen during or after sex, and bleeding during or after sex or between periods. It can also cause heavy periods.
In men, chlamydia can cause pain or a burning sensation when urinating, a white, cloudy or watery discharge from the tip of the penis, and pain or tenderness in the testicles.
It's also possible to have a chlamydia infection in your rectum (bottom), throat or eyes.
Diagnosing chlamydia is done with a urine test or by taking a swab of the affected area. The infection is easily treated with antibiotics, but can lead to serious long-term health problems if left untreated, including infertility.
Read more about chlamydia.
Genital warts are small fleshy growths, bumps or skin changes that appear on or around your genital or anal area. They're caused by the human papilloma virus (HPV) and are the second most common STI in England after chlamydia.
The warts are usually painless, but you may notice some itching or redness. Occasionally, they can cause bleeding.
You don't need to have penetrative sex to pass the infection on because HPV is spread by skin-to-skin contact.
Several treatments are available for genital warts, including creams and freezing the warts (cryotherapy).
Read more about genital warts.
Genital herpes is a common infection caused by the herpes simplex virus (HSV), which is the same virus that causes cold sores.
Some people develop symptoms of HSV a few days after coming into contact with the virus. Small, painful blisters or sores usually develop, which may cause itching or tingling, or make it painful to urinate.
After you've been infected, the virus remains dormant (inactive) most of the time. However, certain triggers can reactivate the virus, causing the blisters to develop again, although they're usually smaller and less painful.
It's easier to test for HSV if you have symptoms. Although there's no cure for genital herpes, the symptoms can usually be controlled using antiviral medicines.
Read more about genital herpes.
Gonorrhoea is a bacterial STI easily passed on during sex. About 50% of women and 10% of men don't experience any symptoms and are unaware they're infected.
In women, gonorrhoea can cause pain or a burning sensation when urinating, a vaginal discharge (often watery, yellow or green), pain in the lower abdomen during or after sex, and bleeding during or after sex or between periods, sometimes causing heavy periods.
In men, gonorrhoea can cause pain or a burning sensation when urinating, a white, yellow or green discharge from the tip of the penis, and pain or tenderness in the testicles.
It's also possible to have a gonorrhoea infection in your rectum, throat or eyes.
Gonorrhoea is diagnosed using a urine test or by taking a swab of the affected area. The infection is easily treated with antibiotics, but can lead to serious long-term health problems if left untreated, including infertility.
Read more about gonorrhoea.
Syphilis is a bacterial infection that in the early stages causes a painless, but highly infectious, sore on your genitals or around the mouth. The sore can last up to six weeks before disappearing.
Secondary symptoms such as a rash, flu-like illness or patchy hair loss may then develop. These may disappear within a few weeks, after which you'll have a symptom-free phase.
The symptoms of syphilis can be difficult to recognise. A simple blood test can usually be used to diagnose syphilis at any stage. The condition can be treated with antibiotics, usually penicillin injections. When syphilis is treated properly, the later stages can be prevented.
Read more about syphilis.
HIV is most commonly passed on through unprotected sex. It can also be transmitted by coming into contact with infected blood - for example, sharing needles to inject steroids or drugs.
The HIV virus attacks and weakens the immune system, making it less able to fight infections and disease. There's no cure for HIV, but there are treatments that allow most people to live a long and otherwise healthy life.
AIDS is the final stage of an HIV infection, when your body can no longer fight life-threatening infections.
Most people with HIV look and feel healthy and have no symptoms. When you first develop HIV, you may experience a flu-like illness with a fever, sore throat or rash. This is called a seroconversion illness.
A simple blood test is usually used to test for an HIV infection. Some clinics may also offer a rapid test using a finger-prick blood test or saliva sample.
Trichomoniasis is an STI caused by a tiny parasite called Trichomonas vaginalis (TV). It can be easily passed on through sex and most people don't know they're infected.
In women, trichomoniasis can cause a frothy yellow or watery vaginal discharge that has an unpleasant smell, soreness or itching around the vagina, and pain when passing urine.
In men, trichomoniasis rarely causes symptoms. You may experience pain or burning after passing urine, a whitish discharge, or an inflamed foreskin.
Trichomoniasis can sometimes be difficult to diagnose and your GP may suggest you go to a specialist clinic for a urine or swab test. Once diagnosed, it can usually be treated with antibiotics.
Read more about trichomoniasis.
Pubic lice ("crabs") are easily passed to others through close genital contact. They're usually found in pubic hair, but can live in underarm hair, body hair, beards and occasionally eyebrows or eyelashes.
The lice crawl from hair to hair but don't jump or fly from person to person. It may take several weeks for you to notice any symptoms. Most people experience itching, and you may notice the lice or eggs on the hairs.
Pubic lice can usually be successfully treated with special creams or shampoos available over the counter in most pharmacies or from a GP or GUM clinic. You don't need to shave off your pubic hair or body hair.
Read more about pubic lice.
Scabies is caused by tiny mites that burrow into the skin. It can be passed on through close body or sexual contact, or from infected clothing, bedding or towels.
If you develop scabies, you may have intense itching that's worse at night. The itching can be in your genital area, but it also often occurs between your fingers, on wrists and ankles, under your arms, or on your body and breasts.
You may have a rash or tiny spots. In some people, scabies can be confused with eczema. It's usually very difficult to see the mites.
Scabies can usually be successfully treated using special creams or shampoos available over the counter in most pharmacies, or from a GP or GUM clinic. The itching can sometimes continue for a short period, even after effective treatment.
Read more about scabies.
Article provided by NHS Choices