Sexually transmitted infections, commonly called STIs, are infections that can be passed from one person to another primarily through sexual contact.
Transmission can occur during vaginal, anal or oral sex. Some infections can also spread through contact with infected blood, shared injecting equipment, pregnancy, childbirth or breastfeeding.
A person may have an STI without noticing any symptoms. This means someone can feel completely healthy and still transmit an infection to another person. Testing, timely treatment and honest communication with sexual partners are therefore important parts of prevention.
What Are Sexually Transmitted Infections?
Sexually transmitted infections are caused by bacteria, viruses, parasites and, less commonly, other organisms.
More than 30 different pathogens can be transmitted through sexual contact. The four major curable STIs are:
Chlamydia
Gonorrhoea
Syphilis
Trichomoniasis
Important viral STIs include:
Human immunodeficiency virus, or HIV
Genital herpes caused by herpes simplex virus
Human papillomavirus, or HPV
Hepatitis B
Many bacterial and parasitic STIs can be cured with appropriate medicines. Viral infections cannot always be eliminated completely, but treatment can control the infection, reduce symptoms, prevent complications and lower the risk of transmission.
For example, antiretroviral treatment allows people living with HIV to remain healthy. A person living with HIV who takes treatment and maintains an undetectable viral load does not sexually transmit HIV.
How Are STIs Transmitted?
STIs are mainly transmitted through sexual contact involving the vagina, penis, anus or mouth.
Transmission may occur through:
Vaginal sex
Infections can pass through semen, vaginal fluids, blood or contact with infected skin and mucous membranes.
Anal sex
The lining of the rectum is delicate and may develop small injuries during sex, making it easier for infections to enter the body.
Oral sex
Oral sex can transmit infections such as gonorrhoea, syphilis, herpes, chlamydia, HPV and, less commonly, HIV.
Skin-to-skin sexual contact
Some infections, particularly herpes, HPV and syphilis, can spread through contact with infected skin or sores that may not be covered by a condom.
Blood exposure
HIV, hepatitis B and hepatitis C can be transmitted through infected blood. Risks include sharing needles, syringes or other injecting equipment and receiving blood that has not been properly screened.
Mother-to-child transmission
Some infections can pass from a pregnant woman to her baby during pregnancy, childbirth or breastfeeding.
These include:
HIV
Syphilis
Hepatitis B
Herpes
Gonorrhoea
Chlamydia
Early antenatal care, screening and treatment can prevent many of these infections from reaching the baby.
Can STIs Spread Through Casual Contact?
Most STIs are not spread through:
Hugging
Shaking hands
Sharing plates or cutlery
Sitting beside an infected person
Using the same toilet
Coughing or sneezing
Ordinary social contact
However, sores or infectious fluids may create risks in specific circumstances. Personal items that may contain blood, such as needles or razors, should not be shared.
Important Facts About STIs
Sexually transmitted infections remain a major global health problem.
The World Health Organization estimates that more than one million curable STIs are acquired every day among people aged 15 to 49 years. Most of these infections do not initially produce noticeable symptoms.
Approximately 374 million new infections with chlamydia, gonorrhoea, syphilis and trichomoniasis occur annually among people aged 15 to 49 years.
Other important facts include:
Hundreds of millions of people live with genital herpes.
HPV is extremely common among sexually active people.
Persistent infection with high-risk HPV types can cause cervical cancer and several other cancers.
Untreated gonorrhoea and chlamydia can cause pelvic inflammatory disease, ectopic pregnancy and infertility.
Syphilis during pregnancy may result in miscarriage, stillbirth, premature birth, congenital infection or death of the baby.
Some STIs increase a person’s susceptibility to HIV.
Gonorrhoea is becoming increasingly difficult to treat because of antimicrobial resistance.
Vaccines are available against hepatitis B and several cancer-causing types of HPV.
Common Signs and Symptoms
Many STIs cause no symptoms. When symptoms occur, they vary according to the infection and the affected part of the body.
Possible symptoms include:
Unusual vaginal discharge
Discharge from the penis
Pain or burning during urination
Genital itching or irritation
Sores, blisters, ulcers or warts around the genitals, anus or mouth
Pain during sex
Lower abdominal or pelvic pain
Painful or swollen testicles
Bleeding between menstrual periods
Bleeding after sex
Rectal pain, discharge or bleeding
Sore throat following oral sexual exposure
Skin rash, including a rash on the palms or soles
Swollen lymph nodes
Fever or general weakness
The absence of symptoms does not mean that a person is free from infection.
When Should You Get Tested?
Testing should be considered when:
You notice symptoms suggestive of an STI.
A sexual partner has been diagnosed with an STI.
You have had sex without a condom.
A condom broke or slipped during sex.
You have a new sexual partner.
You or your partner have multiple sexual partners.
You are pregnant or planning a pregnancy.
You have shared needles or injecting equipment.
You have experienced sexual violence.
A healthcare professional recommends routine screening.
People who are sexually active should discuss their individual risks and suitable testing frequency with a healthcare professional.
Current guidance recommends annual chlamydia and gonorrhoea screening for sexually active women younger than 25 years. Women aged 25 years or older may also require annual screening when they have risk factors such as a new partner, multiple partners or a partner with an STI.
Pregnant women should receive early screening for infections including HIV, syphilis and hepatitis B. Additional tests may be needed according to risk, local guidelines and stage of pregnancy.
How STIs Are Diagnosed
There is no single test that detects every STI. The correct test depends on the suspected infection, symptoms, exposure and part of the body involved.
A healthcare professional may use:
A urine sample
A blood sample
A vaginal swab
A cervical swab
A urethral swab
A throat swab
A rectal swab
A swab from a sore or blister
A physical examination
People should tell the healthcare worker about the types of sexual exposure they have had. A urine or genital test alone may miss an infection in the throat or rectum.
Testing for chlamydia and gonorrhoea
Nucleic-acid amplification tests, commonly called NAATs, are generally the preferred tests.
Depending on the site of exposure, samples may include:
First-catch urine
A vaginal swab
A cervical swab
A urethral swab
A rectal swab
A throat swab
Self-collected vaginal swabs may be available in some health facilities.
Cultures may be required in selected cases, especially when treatment failure or antibiotic-resistant gonorrhoea is suspected.
Testing for syphilis
Syphilis is usually diagnosed through a combination of blood tests.
These commonly include:
A non-treponemal test such as rapid plasma reagin, or RPR
A non-treponemal test such as the Venereal Disease Research Laboratory test, or VDRL
A treponemal antibody test used as part of the testing algorithm
Rapid syphilis tests may also be available.
No single blood result should always be interpreted in isolation. The healthcare professional considers the type of test, symptoms, previous treatment and possible stage of infection.
Testing for HIV
Modern HIV diagnosis normally begins with an approved rapid diagnostic test or laboratory antigen-and-antibody test.
A reactive result must be confirmed through the nationally approved HIV testing algorithm before an HIV-positive diagnosis is made.
The Western blot test is no longer routinely used as the standard confirmatory test in many modern HIV testing programmes.
An HIV viral-load test measures the amount of HIV in the blood. It is mainly used to monitor treatment response in a person already diagnosed with HIV, although nucleic-acid tests may be used for specialised diagnostic situations.
Anyone who may have been exposed to HIV within the previous 72 hours should seek urgent medical care to discuss post-exposure prophylaxis, known as PEP.
Testing for hepatitis B
Hepatitis B testing may include:
Hepatitis B surface antigen, or HBsAg
Antibody to hepatitis B surface antigen, or anti-HBs
Total antibody to hepatitis B core antigen, or total anti-HBc
These markers help determine whether a person has an active infection, has recovered from a previous infection, has immunity from vaccination or remains susceptible.
Testing for genital herpes
When a fresh blister or sore is present, a healthcare professional may collect a swab for a nucleic-acid amplification or PCR test.
Viral culture may also be used, although it becomes less sensitive as a sore begins to heal.
Type-specific blood antibody testing may be useful in selected circumstances, but it has limitations and is not recommended as a general screening test for everyone without symptoms.
Testing and screening for HPV
There is no routine blood test for genital HPV.
Visible genital warts may be diagnosed through clinical examination.
Cervical screening may involve:
An HPV test
Cervical cytology, commonly called a Pap smear
HPV testing combined with cytology
The recommended method and screening interval depend on age, medical history and the national cervical-cancer screening programme.
Applying vinegar to the genitals is not recommended as a routine test because it is not sufficiently specific and may produce misleading results.
Treatment of Sexually Transmitted Infections
Treatment depends on the particular infection.
Chlamydia
Chlamydia can be cured with prescribed antibiotics. Sexual partners may also require testing and treatment.
Gonorrhoea
Gonorrhoea can usually be cured with appropriate antibiotics. However, antimicrobial resistance is an increasing global threat. Treatment should follow current national guidance rather than unprescribed medicines.
WHO identifies rapidly increasing gonococcal antimicrobial resistance as a major threat to STI control.
Syphilis
Syphilis can be cured with antibiotics. The exact treatment depends on the stage of infection, pregnancy status and whether the nervous system or eyes are affected.
Treatment during pregnancy is essential to protect both the mother and baby.
Trichomoniasis
Trichomoniasis is treated with prescribed antiprotozoal medication. Sexual partners usually need treatment to prevent reinfection.
Genital herpes
Herpes cannot currently be eliminated from the body. Antiviral medicines can:
Shorten outbreaks
Reduce pain and discomfort
Decrease how often outbreaks occur
Lower, but not completely remove, the risk of transmission
HIV
HIV is treated with antiretroviral therapy.
Treatment suppresses the virus, protects the immune system and allows people living with HIV to live long and healthy lives.
A person who maintains an undetectable viral load does not sexually transmit HIV. This principle is known as Undetectable Equals Untransmittable, or U=U.
Hepatitis B
Acute hepatitis B may only require monitoring and supportive care.
Some people with chronic hepatitis B require antiviral treatment and regular monitoring for liver damage. Not every infected person requires immediate antiviral medication, so treatment should be determined by a qualified clinician.
HPV and genital warts
There is no medicine that directly eliminates HPV itself, but the immune system clears many infections over time.
Genital warts can be treated with prescribed topical medicines or procedures such as freezing, cauterisation or surgical removal.
Abnormal cervical cells can be monitored or treated to prevent progression to cervical cancer.
Why Self-Medication Is Dangerous
People should not treat suspected STIs with antibiotics purchased without proper testing and medical advice.
Self-medication can:
Delay the correct diagnosis
Fail to cure the infection
Hide symptoms temporarily
Increase antibiotic resistance
Cause harmful side effects
Allow complications to develop
Leave sexual partners untreated
Completing the prescribed treatment is important even when symptoms improve quickly.
Partner Testing and Treatment
Treating only one person may result in reinfection if a sexual partner remains infected.
A person diagnosed with an STI should follow professional advice about:
Informing recent sexual partners
Partner testing
Partner treatment
Avoiding sexual contact temporarily
Using condoms after treatment
Returning for repeat testing
Partner notification should be handled respectfully, confidentially and without violence or blame.
How to Prevent STIs
No single method prevents every STI in every situation. Combining several methods provides stronger protection.
1. Use condoms correctly and consistently
External and internal condoms reduce the risk of HIV and many other STIs when used correctly during vaginal, anal or oral sex.
Condoms offer less complete protection against infections spread from skin that is not covered, including herpes, HPV and syphilis sores outside the covered area.
2. Receive recommended vaccines
Vaccination can prevent:
Hepatitis B
Several high-risk and wart-causing types of HPV
HPV vaccination is most effective when given before exposure to the virus. Nigeria introduced HPV vaccination into its immunisation programme for eligible girls.
Parents can read AnjKreb’s guide to the immunisation schedule in Nigeria for information about childhood vaccines, including HPV and hepatitis B vaccination.
3. Get tested
Testing allows infections to be identified and treated before they cause complications or spread to other people.
Testing is especially important because many STIs do not cause noticeable symptoms.
4. Reduce the number of sexual partners
Having fewer sexual partners can reduce exposure, particularly when both partners have been tested and remain mutually monogamous.
5. Communicate before sexual contact
Partners should discuss:
Recent STI testing
Condom use
Vaccination
Current symptoms
Known infections
HIV prevention options
A person who has sores, unusual discharge, painful urination or another suspected symptom should avoid sexual contact and seek medical care.
6. Use HIV prevention services
HIV-negative people with ongoing exposure may benefit from pre-exposure prophylaxis, known as PrEP.
A person with a possible recent exposure should seek PEP urgently. PEP must be started as soon as possible and no later than 72 hours after exposure.
7. Do not share injecting equipment
Never share needles, syringes or equipment used to prepare injections.
8. Attend antenatal care early
Pregnant women should register for antenatal care early and complete recommended screening for HIV, syphilis, hepatitis B and other infections.
Early diagnosis and treatment can prevent serious complications and mother-to-child transmission.
9. Consider voluntary medical male circumcision
Medical male circumcision reduces the risk of heterosexual HIV acquisition in men and may provide some protection against certain other infections.
It does not provide complete protection and should be combined with condoms, HIV testing and other prevention methods.
Possible Complications of Untreated STIs
Untreated infections may result in:
Pelvic inflammatory disease
Chronic pelvic pain
Infertility
Ectopic pregnancy
Testicular or epididymal inflammation
Pregnancy complications
Infection of a newborn
Blindness or disability in an infected baby
Liver disease
Neurological or cardiovascular complications of syphilis
Cervical and other HPV-related cancers
Increased risk of acquiring or transmitting HIV
Early diagnosis can prevent many of these outcomes.
When to Seek Medical Care
Visit a qualified health facility when you have:
Genital sores, blisters or warts
Unusual vaginal or penile discharge
Pain or burning during urination
Pelvic or lower abdominal pain
Testicular pain or swelling
Bleeding after sex
A rash following possible sexual exposure
A partner recently diagnosed with an STI
Possible exposure to HIV within the previous 72 hours
Symptoms during pregnancy
Severe pelvic pain, fever, fainting, heavy bleeding or testicular pain should be assessed urgently.
Frequently Asked Questions
Can someone have an STI without symptoms?
Yes. Many STIs produce no symptoms or only mild symptoms. Testing may be the only way to know.
Can toilet seats transmit STIs?
STIs are not normally acquired from toilet seats. The organisms generally do not survive or spread effectively through this type of casual contact.
Can oral sex transmit an STI?
Yes. Oral sex can transmit gonorrhoea, chlamydia, syphilis, herpes, HPV and other infections.
Can condoms prevent every STI?
Condoms significantly reduce the risk of many infections but do not completely protect skin that they do not cover.
Are all STIs curable?
No. Chlamydia, gonorrhoea, syphilis and trichomoniasis are generally curable with the correct treatment. HIV and herpes can be effectively controlled but are not currently cured by routine treatment.
Can an STI come back after treatment?
A cured infection can be acquired again if a person is re-exposed. This is why partner treatment and prevention are important.
Should both partners receive treatment?
For several infections, partners need evaluation and treatment to prevent reinfection. The specific recommendation depends on the STI.
Can STI treatment affect fertility?
Correct treatment protects fertility by preventing complications. Untreated gonorrhoea and chlamydia are more likely to damage fertility than properly prescribed treatment.
Conclusion
Sexually transmitted infections are common, and many cause no obvious symptoms.
Anyone who is sexually active can benefit from accurate information, appropriate vaccination, correct condom use, timely testing and early treatment.
STIs should not be associated with shame. They are health conditions that require confidential, respectful and evidence-based care.
Do not rely on symptoms or self-medication. Visit a recognised healthcare facility for testing and complete the treatment prescribed. Sexual partners may also need testing or treatment to prevent reinfection and further transmission.
Last fact-checked and updated: July 2026
Medical Disclaimer
This article is intended for general health education. It does not replace testing, diagnosis or treatment from a qualified healthcare professional. Seek medical care if you have symptoms, a known exposure or concerns about your sexual health.
Author Bio
Adeyinka Joseph Alonge is a public health professional, researcher and writer with interests spanning health, science, technology, personal development and practical knowledge for everyday life.
Sources and Further Reading
World Health Organization. Sexually transmitted infections fact sheet. Updated September 2025.
https://www.who.int/news-room/fact-sheets/detail/sexually-transmitted-infections-%28stis%29World Health Organization. Sexually transmitted infections health topic.
https://www.who.int/health-topics/sexually-transmitted-infectionsUnited States Centers for Disease Control and Prevention. STI Treatment Guidelines.
https://www.cdc.gov/std/treatment-guidelines/default.htmUnited States Centers for Disease Control and Prevention. Getting Tested for STIs.
https://www.cdc.gov/sti/testing/index.htmlWorld Health Organization. Gonorrhoea fact sheet.
https://www.who.int/news-room/fact-sheets/detail/gonorrhoea-%28neisseria-gonorrhoeae-infection%29
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