Overview
STIs are infections passed mainly through sexual contact, including vaginal, anal, and oral sex. They can be caused by bacteria, viruses, or parasites. Some STIs can also spread through blood or from a pregnant person to a baby. Many people feel well and do not know they have an infection.
Key Symptoms
Some STIs cause no symptoms at all. When symptoms happen, they may include sores, blisters, rash, unusual discharge, pain when urinating, pelvic or testicular pain, itching, bleeding after sex, or flu-like symptoms. Symptoms can vary by infection and by body part affected, such as the genitals, rectum, throat, or mouth.
Causes and Risk Factors
Risk can be higher if you have sex without barrier protection, have a new or multiple partners, or do not know a partner's STI status. A past STI can raise the chance of another STI. Shared needles can spread infections such as HIV and hepatitis B. Alcohol or drug use may also increase risk if it makes safer-sex planning harder.
Who Is Affected
Anyone who is sexually active can get an STI, regardless of age, gender, sexual orientation, or relationship status. Some groups may face higher risk because of exposure, barriers to healthcare, stigma, or reduced access to testing and prevention tools. Young people are often advised to learn about testing and prevention early because infections can occur soon after sexual activity begins.
Prevention
Ways to lower risk include using condoms or dental dams correctly during sex, limiting exposure by discussing testing with partners, and avoiding sex when sores or symptoms are present. Vaccination can help prevent HPV and hepatitis B. Regular screening, HIV prevention options such as pre-exposure prophylaxis for some people, and not sharing needles are also important prevention steps.
Diagnosis and Tests
Testing may involve urine samples, blood tests, swabs, or a physical examination, depending on the infection and the body site involved. Because many STIs cause no symptoms, testing may be recommended based on sexual practices, pregnancy, age, or local guidelines even when you feel well. Ask a healthcare professional which tests are appropriate for you and whether throat, rectal, or genital testing is needed.
Treatment Categories
Treatment depends on the cause. Bacterial and parasitic STIs are often treated with prescription medicines, while viral STIs may be managed with antiviral treatment and monitoring. Partners may also need evaluation and treatment, and follow-up testing may be advised. Avoid sexual contact until a healthcare professional tells you when it is appropriate to resume.
When to Seek Medical Care
Seek medical care if you have sores, discharge, pain with urination, pelvic pain, testicular pain, rash, bleeding after sex, or if a partner tells you they have an STI. Testing is also important after unprotected sex, condom breakage, sexual assault, or sharing needles. If you are pregnant or think you may be pregnant, STI testing is especially important because some infections can affect the baby.
Questions to Ask a Healthcare Professional
You may want to ask which STI tests you need, when to test after a possible exposure, and whether you need testing at more than one body site. Ask how to reduce risk in the future, whether vaccines may help, and whether your partner or partners should be tested. If you receive a diagnosis, ask about follow-up, how to avoid passing the infection to others, and when to seek urgent care.