🛡️ What is a sexually transmitted infection?
A sexually transmitted infection (STI) is an infection caused by bacteria, viruses, parasites or other microorganisms that can be transmitted primarily through sexual contact.
Transmission may occur during vaginal, anal or oral sex. Some infections may also spread through intimate skin-to-skin contact, blood, shared injection equipment, or from mother to baby during pregnancy or childbirth.
🔬 Common sexually transmitted infections
A bacterial infection that frequently causes no symptoms. It may affect the genital tract, rectum and other exposed sites. Untreated infection can lead to complications including pelvic inflammatory disease.
A bacterial infection that can affect the urethra, cervix, rectum and throat. It may cause discharge or painful urination but can also remain asymptomatic.
A bacterial infection that develops in stages. It may begin with a painless sore and later cause rash or other manifestations. Untreated infection can eventually affect the nervous system and other organs.
A virus that affects the immune system. Highly effective treatments can now control the infection. Testing allows people to know their status and access medical care early.
A very common infection. Most infections cause no major problems, but some HPV types can cause genital warts while others are associated with several cancers.
Usually caused by herpes simplex viruses. It can cause painful blisters or ulcers, although many people have mild or unrecognized symptoms.
A parasitic infection that may cause discharge, irritation or painful urination. Many infected people have no symptoms.
It can spread through sexual contact and blood exposure. An effective vaccine is available to prevent hepatitis B.
It is primarily transmitted through blood exposure. Sexual transmission is less common but can occur in certain situations. There is currently no hepatitis C vaccine.
👀 Possible symptoms
Sores, blisters, warts, unusual discharge, itching, irritation or pain.
Burning, pain or discomfort during urination may occur with some infections.
Pelvic pain, pain during sex or abnormal bleeding may require medical evaluation.
STIs can also affect these sites depending on sexual practices and the microorganism involved.
Some infections can cause rash, warts, ulcers or other skin lesions.
This is particularly important: feeling completely well does not necessarily mean that an infection is absent.
🧪 How are STIs diagnosed?
There is no single test that detects every STI. Testing depends on the infection, symptoms and which parts of the body were exposed.
Used for certain infections including HIV, syphilis and hepatitis.
Urine testing can identify certain bacterial infections in appropriate clinical situations.
Vaginal, cervical or urethral samples may be used to identify specific microorganisms.
After certain exposures, throat or rectal testing may be needed. A urine test alone may not evaluate these sites.
🛡️ Reducing the risk
Correct and consistent use of barrier methods substantially reduces the risk of many STIs.
Knowing your own and your partner's sexual health status can identify infections that cause no symptoms.
Vaccines are available to prevent HPV-related infections and hepatitis B. Hepatitis A vaccination is also recommended for certain groups.
Reducing the number of sexual partners and mutual monogamy with a tested partner can lower risk.
Sharing needles or other injection equipment can transmit HIV and viral hepatitis.
Discussing testing, prevention and sexual health before a new relationship can support informed decisions.
💊 HIV: PrEP and PEP are different
Pre-exposure prophylaxis is an HIV prevention strategy for people without HIV who may be exposed to the virus. It requires appropriate medical assessment and follow-up.
Post-exposure prophylaxis is an emergency HIV prevention intervention after certain potential exposures and should be assessed as soon as possible.
🚨 Recent possible HIV exposure
If a possible HIV exposure has occurred, do not wait for symptoms.
- Seek medical evaluation immediately.
- PEP should be started as soon as possible when indicated.
- The recommended maximum window to start PEP is 72 hours after exposure.
- The earlier the exposure is assessed, the better.
- Testing for other STIs and viral hepatitis may also be appropriate.
🧬 HPV, vaccination and cancer
Human papillomavirus is extremely common. Most infections do not cause major health problems, but some HPV types can cause genital warts and others are associated with cancers of the cervix, anus, penis, vulva, vagina and oropharynx.
Vaccination can prevent many HPV infections and their complications. The vaccine prevents new infections; it does not treat an infection that is already present.
🤰 STIs and pregnancy
Some STIs can affect pregnancy or be transmitted to a baby during pregnancy or childbirth. This is why certain STI tests are part of prenatal care.
CDC recommends testing for syphilis, HIV, hepatitis B and hepatitis C early in pregnancy, with additional or repeat testing when indicated.
⚠️ When should you seek medical care?
- After a possible exposure to an STI.
- New sores, blisters or lesions involving the genitals, mouth or anus.
- New or abnormal genital discharge.
- Pain or burning during urination.
- Significant or persistent pelvic pain.
- Rectal pain or discharge after sexual exposure.
- An unexplained rash, particularly with other symptoms.
- A sexual partner has been diagnosed with an STI.
- Possible HIV exposure within the previous 72 hours.
❓ Frequently asked questions
Can I have an STI without symptoms?
Yes. Many STIs frequently cause no symptoms. Appropriate testing is the way to identify many of these infections.
Can oral sex transmit STIs?
Yes. Several STIs can be transmitted through oral sex and may infect the mouth or throat.
Does a urine test detect every STI?
No. Depending on the infection and exposure, blood tests or vaginal, urethral, throat, rectal or lesion samples may be necessary.
Do condoms provide 100% protection?
They greatly reduce the risk of many STIs when used correctly, but HPV, herpes and syphilis can sometimes involve skin that is not covered by a condom.
Does birth control protect against STIs?
Non-barrier contraception such as pills, IUDs, implants, patches and rings does not protect against sexually transmitted infections.
Are all STIs curable?
No. Many bacterial and parasitic infections can be cured with appropriate treatment. Some viral infections can be effectively controlled but may not be eliminated from the body.
📚 Medical references
Current information on STI prevention, testing, diagnosis and sexual health.
Mayo ClinicClinical information about STI symptoms, diagnosis, prevention and complications.
Hospital Clínic BarcelonaMedical information about transmission, prevention, diagnostic testing and post-exposure assessment.