Sexo y salud sexual

Sexually transmitted infections (STIs)

Revisado: 4 de octubre de 2026

Solo en inglés por ahora

STIs are very common and often cause no symptoms. Testing is quick and routine, and every STI can be treated, with many cured completely.

What STIs are

Sexually transmitted infections (STIs) are infections that pass from one person to another through sexual contact, including vaginal, anal and oral sex. They can be caused by bacteria, viruses or parasites. STIs are very common. Worldwide, more than 1 million curable STIs are passed on every day among people aged 15 to 49. Some STIs can also pass from a mother to her baby during pregnancy, birth or breastfeeding.

The most common STIs

Four common STIs can usually be cured with antibiotics: chlamydia, gonorrhoea, syphilis and trichomoniasis. Four others are caused by viruses: herpes, HIV, hepatitis B and human papillomavirus (HPV). These cannot be cured, but medicines can help control herpes and HIV, and most HPV infections clear by themselves. Vaccines can protect against HPV and hepatitis B.

Signs to look out for

Many STIs cause no symptoms, so you can have one without knowing and pass it on. When there are signs, they can include unusual discharge from the vagina or anus, pain when you pee, itching around the genitals or anus, a rash, and unusual bleeding from the vagina. Lumps, warts, blisters or sores around the genitals or anus can also be signs. Some STIs cause pain in the lower tummy.

Getting tested

Testing is the only way to know for sure. Get tested if you have symptoms, a new partner, or a partner with symptoms. STI testing is a routine part of health care. In many places you can go to a sexual health clinic without a referral, and some clinics offer home testing kits. Tests usually involve a pee sample, a swab or a blood test. Some STIs can take up to 7 weeks after sex to show up on a test.

Treatment and telling partners

If a test shows an STI, you will be offered treatment. Many STIs are treated with antibiotics. Take all of the treatment you are given. Your current partners, and recent ex-partners, should be told so they can get tested and treated too. If you would rather not tell them yourself, the clinic can often do this for you without giving your name. Using condoms correctly every time you have sex is one of the best ways to lower your risk.

Why it matters and when to act fast

Untreated STIs can cause lasting problems. Chlamydia and gonorrhoea are major causes of pelvic inflammatory disease (PID) and infertility. Herpes, gonorrhoea and syphilis can raise the chance of getting HIV, and HPV can cause cervical and other cancers. Get urgent medical help if you have severe pain in your lower tummy with a high temperature, being sick or feeling very unwell. This can be a sign of PID. If you think you have been exposed to HIV, go to a sexual health clinic or emergency department straight away. Medicine called PEP can lower the chance of infection, but it must be started within 72 hours.

This is general information, not a diagnosis. If you have symptoms or think you may have an STI, get tested at a sexual health clinic or by a doctor or nurse.