Health Issue
Sexually Transmitted Infections (STIs): Symptoms, Types, Causes, Transmission, and Testing
Sexually Transmitted Infections (STIs) are infections primarily transmitted through sexual activity. STIs can be caused by bacteria, viruses, or parasites and can be transmitted through vaginal, anal, or oral sex.
It's important to note that someone can have an STI without experiencing any symptoms. Therefore, someone who appears healthy may not necessarily be free from a sexually transmitted infection.
According to the World Health Organization (WHO), more than 1 million curable sexually transmitted infections occur every day among people aged 15–49 worldwide. In 2020, an estimated 374 million new infections occurred due to chlamydia, gonorrhea, syphilis, and trichomoniasis.
What is STI?
An STI is an infection transmitted primarily through sexual contact. The term STI emphasizes the presence of the infection, while the term STD (sexually transmitted disease) refers to the condition when the infection causes illness or symptoms.
More than 30 types of bacteria, viruses, and parasites are known to be transmitted through sexual contact. Some can also be transmitted from mother to child during pregnancy or childbirth, as well as through infected blood.
Some of the most well-known STIs include:
- Chlamydia (Chlamydia trachomatis)
- Gonorrhea
- Syphilis
- Trichomoniasis
- HIV
- Genital herpes (HSV)
- Human papillomavirus (HPV)
- Hepatitis B
The four main STIs—chlamydia, gonorrhea, syphilis, and trichomoniasis—are currently curable with proper treatment. Meanwhile, some viral infections, such as HIV, herpes, and HPV, require different medical treatments and monitoring.
How are STIs transmitted?
STIs can be transmitted through:
1. Unprotected vaginal intercourse.
2. Anal sexual intercourse.
3. Oral sexual intercourse.
4. Direct contact with the genital area or an infected wound in some types of STIs.
5. Transmission from mother to baby during pregnancy or childbirth for certain infections.
6. Exposure to infected blood under certain conditions.
Correct and consistent condom use can help reduce the risk of contracting many STIs. However, condoms do not provide 100% protection against all STIs, especially infections that can spread through skin areas not covered by the condom, such as herpes and syphilis.
What are the symptoms of STIs?
STI symptoms can vary depending on the type of infection. In fact, many people experience no symptoms at all.
If symptoms appear, some signs that may occur include:
• Unusual discharge from the vagina or penis
• Pain or burning sensation when urinating
• Sores, abrasions, or lumps in the genital area
• Itching or irritation in the genital area
• Pain during sexual intercourse
• Pain in the lower abdomen
• Unusual vaginal bleeding
• Swelling or pain in the testicles
• Rashes on the skin in certain conditions
• Fever or feeling unwell in some types of infection
However, the absence of symptoms does not mean that a person is definitely free from STIs. A systematic review and meta-analysis published in 2024 found that most chlamydia, gonorrhea, and trichomoniasis infections in women in low- and middle-income countries can be asymptomatic.
A systematic review and meta-analysis published in 2024 found that most chlamydia, gonorrhea, and trichomoniasis infections in women in low- and middle-income countries can be asymptomatic. This is one reason why screening can be important, especially for people who have risk factors or have had risky exposures.
Why Should We Be Wary of STI?
Undetected and untreated STIs can lead to health complications.
In women, certain infections, such as chlamydia and gonorrhea, can cause pelvic inflammatory disease (PID) . This condition can damage the reproductive tract and increase the risk of infertility.
Research and scientific reviews also suggest a link between certain sexually transmitted infections and female fertility issues. A scoping review published in 2025 found that several studies suggest a link between Chlamydia trachomatis infection before pregnancy and fertility problems, although the researchers emphasized that the available evidence is limited and further research is needed.
STIs can also increase the risk of contracting HIV. The presence of sores or inflammation in the genital area can make it easier for HIV to enter the body.
During pregnancy, some STIs can cause complications for both mother and baby. Syphilis, for example, can be transmitted from mother to fetus and is associated with various pregnancy complications. The WHO estimates that approximately 1.1 million pregnant women will develop syphilis in 2022, and the infection will contribute to more than 390,000 adverse pregnancy outcomes.
Can STI be cured?
It depends on the type of infection.
STIs caused by certain bacteria or parasites can be cured with appropriate treatment. Examples include chlamydia, gonorrhea, syphilis, and trichomoniasis.
Meanwhile, viral infections like HIV, herpes, and HPV require different treatment approaches. Some can be controlled with medication, but not all can be completely eliminated from the body.
Treatment should be based on a diagnosis and evaluation by a healthcare professional. Taking antibiotics without a doctor's prescription or examination is not recommended, as it can lead to inappropriate treatment and contribute to antimicrobial resistance.
WHO also highlighted that antibiotic resistance in gonorrhea is one of the major challenges in global STI control.
Why is STI Screening Important?
Because many STIs can be asymptomatic, screening can help detect infections early.
STI screening may be considered based on:
• A person's sexual history and risk factors
• Presence of symptoms that indicate STI
• History of sexual partners with STIs
• Previous examination results
• Pregnancy
• Certain health conditions
• Recommendations from doctors or health workers
The type of test used may vary depending on the suspected infection. Tests may use urine, blood, or swab samples from specific locations, depending on the type of infection and the patient's condition.
For chlamydia and gonorrhea, nucleic acid amplification testing (NAAT) is a widely used method. A systematic review conducted for the US Preventive Services Task Force showed that NAAT testing had good accuracy in detecting chlamydia and gonorrhea in a variety of specimen types.
However, not everyone needs all types of STI testing. Testing should be tailored to your symptoms, exposure history, risk factors, and your doctor's recommendations.
How to Prevent STIs?
Some steps that can be taken to reduce the risk of STIs include:
1. Use condoms correctly
Consistent condom use can help reduce the risk of transmission of various STIs.
2. Do a check if there is a risk
Don't wait for symptoms to appear. Some STIs may not cause symptoms but can still be transmitted to partners.
3. Avoid changing sexual partners
Having fewer sexual partners can help reduce the chances of exposure to STIs.
4. Get the available vaccinations
Vaccines are available for some sexually transmitted infections, particularly HPV and hepatitis B.
5. Don't self-medicate
If you have symptoms or positive test results, consult a doctor to get an appropriate diagnosis and therapy.
6. Tell your partner if you are diagnosed with an STI.
For some STIs, sexual partners also need evaluation, testing, and/or treatment to reduce the risk of re-infection. The CDC places partner management as a critical component of STI management.
When Should You Get a Checkup?
Consider consulting a doctor or healthcare professional if you:
• Experiencing unusual vaginal or penile discharge.
• Experiencing pain or burning when urinating.
• Finding sores, blisters, or lumps in the genital area.
• Experiencing pain during sexual intercourse.
• Having a partner diagnosed with an STI.
• Have had risky sexual intercourse.
• Having concerns after a sexual exposure.
• Are planning a pregnancy or are pregnant and require an evaluation for infection risk.
Most importantly, don't be embarrassed to get tested . STIs are a health issue that can happen to anyone and shouldn't be a reason to judge someone.
Conclusion
Sexually Transmitted Infections (STIs) are an important health issue because some infections may not cause symptoms, but can still be transmitted and cause complications.
Proper detection and treatment can help prevent complications, reduce transmission to partners, and maintain sexual and reproductive health.
If you have symptoms, a history of risk exposure, or concerns about STIs, consult your doctor and ask if STI testing is necessary for your condition .
Reference
1. World Health Organization. Sexually transmitted infections (STIs). September 10, 2025.
2. World Health Organization. Sexually transmitted infections – Health Topics.
3. Workowski KA, Bachmann LH, Chan PA, et al. Sexually Transmitted Infections Treatment Guidelines, 2021. MMWR Recommendations and Reports. 2021;70(4):1–187.
4. Cantor A, et al. Screening for Chlamydial and Gonococcal Infections: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA. 2021.
5. Fortas C, Delarocque-Astagneau E, Randremanana RV, et al. Asymptomatic infections with Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis among women in low- and middle-income countries: A systematic review and meta-analysis. PLOS Global Public Health. 2024;4(5):e0003226.
6. Tsevat DG, Wiesenfeld HC, Parks C, Peipert JF. Sexually transmitted diseases and infertility. American Journal of Obstetrics & Gynecology. 2017.
7. Kristensen TS, Foldager A, Laursen ASD, Mikkelsen EM. Sexually transmitted infections (Chlamydia trachomatis, genital HSV, and HPV) and female fertility: A scoping review. Sexual & Reproductive Healthcare. 2025;43:101067.
8. National Institutes of Health. HIV and Sexually Transmitted Infections (STIs). 2025.