Sexually Transmitted Infections: Symptoms, Tests and Treatment

 

  

Updated: August 2026

Sexually transmitted infections, commonly called STIs, are infections that can pass from one person to another primarily through sexual contact.

Transmission can occur during vaginal, anal or oral sex. Some infections can also spread through 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, vaccination where available, condom use and communication with sexual partners are therefore important parts of STI prevention.

What Are Sexually Transmitted Infections?

Sexually transmitted infections are caused by bacteria, viruses, parasites and other microorganisms.

More than 30 different bacteria, viruses and parasites are known to be transmitted through sexual contact.

Four common 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.

Some viral infections cannot currently be eliminated completely, but effective treatment can control infection, reduce complications and, in some cases, dramatically reduce transmission.

For example, antiretroviral treatment allows people living with HIV to live long and healthy lives. A person living with HIV who takes treatment and maintains an undetectable viral load does not sexually transmit HIV. This is known as Undetectable = Untransmittable, or U=U.

How Common Are STIs?

STIs remain a major global public 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, and many of these infections cause no noticeable symptoms.

WHO estimated that approximately 374 million new infections with chlamydia, gonorrhoea, syphilis and trichomoniasis occurred globally in 2020 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 and infertility.
• Syphilis during pregnancy can seriously harm the mother and baby.
• Some STIs increase susceptibility to HIV.
• Antimicrobial resistance is making gonorrhoea increasingly difficult to treat in some settings.
• Vaccines can prevent hepatitis B and important HPV infections.

How Are STIs Transmitted?

STIs are mainly transmitted through sexual contact involving the genitals, anus or mouth.

Vaginal Sex

Infections can spread 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, creating an opportunity for infections to enter the body.

Oral Sex

Oral sex can transmit several infections, including gonorrhoea, syphilis, herpes, chlamydia and HPV.

HIV transmission through oral sex is much less common than through vaginal or anal sex, but other STIs can spread readily through oral sexual contact.

Skin-to-Skin Sexual Contact

Some STIs do not require semen or vaginal fluid for transmission.

Herpes and HPV, for example, can spread through contact with infected genital skin.

Syphilis can spread through direct contact with an infectious sore.

This means condoms can greatly reduce risk but cannot completely prevent infections that involve skin outside the area covered by the condom.

Blood Exposure

HIV, hepatitis B and hepatitis C can be transmitted through infected blood.

Risks include:

• Sharing needles or syringes
• Sharing equipment used to prepare injected drugs
• Unsafe medical injections
• Exposure to contaminated sharp instruments
• Receiving unscreened blood or blood products

Blood donated through properly regulated blood-transfusion systems is screened to reduce these risks.

Mother-to-Child Transmission

Some infections can pass from a pregnant woman to her baby during pregnancy, childbirth or, for certain infections, breastfeeding.

These include:

• HIV
• Syphilis
• Hepatitis B
• Herpes
• Gonorrhoea
• Chlamydia

Early antenatal care, appropriate screening and treatment can prevent many serious complications and reduce mother-to-child transmission.

Can STIs Spread Through Casual Contact?

Most STIs are not spread through ordinary social contact such as:

• Hugging
• Shaking hands
• Sharing plates or cutlery
• Sitting beside someone
• Using the same toilet
• Coughing
• Sneezing
• Sharing a room

However, equipment or personal items contaminated with blood can present risks for blood-borne infections.

Needles and syringes should never be shared.

Can Someone Have an STI Without Symptoms?

Yes.

This is one of the most important facts about sexually transmitted infections.

Chlamydia, gonorrhoea, HPV, herpes, HIV and several other STIs can be present without obvious symptoms.

A person may therefore transmit an infection without knowing that they have it.

This is why testing based on risk and exposure is important rather than relying only on symptoms.

Common Signs and Symptoms of STIs

Symptoms vary according to the infection and the part of the body affected.

Possible symptoms include:

• Unusual vaginal discharge
• Discharge from the penis
• Pain or burning during urination
• Genital itching or irritation
• Sores, blisters or ulcers around the genitals, anus or mouth
• Genital warts
• 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 rashes involving the palms or soles
• Swollen lymph nodes
• Fever or general weakness

The absence of symptoms does not mean that someone is free from an STI.

Vaginal Discharge Does Not Always Mean an STI

Abnormal vaginal discharge can occur with sexually transmitted infections, but not every vaginal condition is an STI.

For example:

Bacterial vaginosis involves an imbalance in the vaginal bacterial environment and commonly causes thin discharge and a fishy vaginal odour.

Vaginal candidiasis, or yeast infection, commonly causes itching, irritation and thick white discharge.

Trichomoniasis, on the other hand, is a sexually transmitted infection that can also cause vaginal discharge.

Because symptoms overlap, persistent vaginal discharge should not automatically be self-diagnosed.

Read our guides to Bacterial Vaginosis and Vaginal Yeast Infection for more information.

When Should You Get Tested for STIs?

Testing should be considered when:

• You develop symptoms suggesting an STI.
• A sexual partner has been diagnosed with an STI.
• You have had sex without a condom.
• A condom broke or slipped.
• You have a new sexual partner.
• You or your partner have multiple sexual partners.
• You are pregnant or planning 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.

Some sexually active people benefit from regular screening even when they have no symptoms.

Current CDC guidance recommends annual chlamydia and gonorrhoea screening for sexually active women younger than 25 years. Women aged 25 years and older may also need screening when risk factors such as a new partner, multiple partners or a partner with an STI are present.

Pregnant women should receive appropriate screening early in pregnancy for infections such as HIV, syphilis and hepatitis B, with additional testing based on clinical risk and national guidance.

STI Testing Is Not One Single Test

There is no single test that detects every sexually transmitted infection.

The correct test depends on:

• The suspected infection
• Symptoms
• Type of exposure
• Time since exposure
• Part of the body exposed
• Pregnancy status
• Medical history

Testing may involve:

• Urine
• Blood
• Vaginal swabs
• Cervical swabs
• Urethral swabs
• Rectal swabs
• Throat swabs
• Swabs from sores or blisters
• Physical examination

It is important to tell the healthcare worker about the type of sexual exposure involved.

For example, a urine or genital test may not detect an infection located only in the throat or rectum.

Testing for Chlamydia and Gonorrhoea

Nucleic-acid amplification tests, commonly called NAATs, are widely used for detecting chlamydia and gonorrhoea.

Depending on the site of exposure, samples may include:

• First-catch urine
• Vaginal swab
• Cervical swab
• Urethral swab
• Rectal swab
• Throat swab

Self-collected vaginal swabs may be available in some healthcare settings.

Cultures may be particularly useful when gonorrhoea treatment failure or antimicrobial resistance is suspected.

Testing for Syphilis

Syphilis is usually diagnosed through blood testing combined with clinical assessment.

Testing commonly uses:

• A non-treponemal test such as RPR or VDRL
• A treponemal antibody test

Some programmes also use rapid syphilis tests.

The interpretation depends on the combination of results, symptoms, previous treatment and possible stage of infection.

No individual blood result should automatically be interpreted without clinical context.

Testing for HIV

Modern HIV diagnosis uses approved rapid diagnostic tests or laboratory-based tests according to national testing algorithms.

A reactive screening result must be confirmed using the approved testing algorithm before an HIV-positive diagnosis is made.

An HIV viral-load test is mainly used to monitor treatment after HIV has been diagnosed. Specialised nucleic-acid testing may also be used in selected diagnostic situations.

Anyone with a possible HIV exposure within the previous 72 hours should seek urgent healthcare to discuss post-exposure prophylaxis, or PEP.

PEP should be started as soon as possible.

Testing for Hepatitis B

Hepatitis B testing may include three important markers:

• 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

Together, these tests can help determine whether someone currently has hepatitis B, has recovered from previous infection, has vaccine-related immunity or remains susceptible.

Testing for Genital Herpes

When a fresh genital blister or sore is present, a healthcare professional can take a sample for molecular testing such as PCR.

Viral culture may also be used in some settings, although its sensitivity decreases as lesions begin to heal.

Blood antibody tests can have a role in selected circumstances but are not recommended as routine screening tests for everyone without symptoms.

Testing and Screening for HPV

There is no routine blood test used to diagnose genital HPV infection.

Visible genital warts are usually diagnosed by clinical examination.

Cervical cancer screening may involve:

• HPV testing
• Cervical cytology, commonly called a Pap smear
• Other screening approaches depending on the programme

HPV testing used for cervical screening should not be confused with diagnosing genital warts.

Read our guide to Genital Warts and HPV: Symptoms, Treatment, Transmission and Cancer Risk for a fuller explanation.

Women can also read our detailed Cervical Cancer guide to understand high-risk HPV, screening and cancer prevention.

How Are STIs Treated?

Treatment depends entirely on the infection.

Chlamydia

Chlamydia is curable with appropriate antibiotics.

Sexual partners may also require testing and treatment to reduce the risk of reinfection.

Gonorrhoea

Gonorrhoea can usually be cured with appropriate antibiotics.

However, antimicrobial resistance is becoming an increasingly serious problem.

WHO continues to report rising resistance to important antibiotics used against gonorrhoea. This makes proper diagnosis, surveillance and adherence to current treatment guidelines increasingly important.

People should not attempt to treat suspected gonorrhoea with unprescribed antibiotics.

Syphilis

Syphilis can be cured with appropriate antibiotic treatment.

The treatment approach depends on factors such as:

• Stage of infection
• Pregnancy
• Neurological involvement
• Eye involvement
• Previous treatment

Treatment during pregnancy is particularly important because untreated maternal syphilis can cause severe pregnancy and newborn complications.

Trichomoniasis

Trichomoniasis is curable with appropriate antiprotozoal treatment.

Sexual partners generally require treatment because reinfection can occur when one partner remains untreated.

Genital Herpes

Herpes cannot currently be eliminated completely from the body.

Antiviral medicines can:

• Shorten outbreaks
• Reduce pain
• Reduce the frequency of outbreaks
• Reduce viral shedding
• Lower the risk of transmission

However, treatment does not completely remove transmission risk.

HIV

HIV is treated with antiretroviral therapy, or ART.

Effective treatment suppresses HIV, protects the immune system and allows people living with HIV to live long and healthy lives.

When a person living with HIV takes treatment and maintains an undetectable viral load, they do not sexually transmit HIV.

This is U=U.

Hepatitis B

Acute hepatitis B often requires monitoring and supportive medical care.

Some people with chronic hepatitis B require long-term antiviral treatment to reduce liver damage and complications.

Not everyone with chronic hepatitis B requires immediate antiviral therapy, so treatment decisions should be based on proper clinical assessment.

HPV and Genital Warts

There is no medicine that directly eliminates HPV itself.

The immune system clears many HPV infections naturally over time.

Visible genital warts can be treated using appropriate topical medicines or healthcare procedures such as:

• Cryotherapy
• Electrosurgery
• Surgical removal
• Selected prescription treatments

Removing a genital wart does not necessarily mean HPV has been eliminated from the body.

Why Self-Medicating STIs Is Dangerous

Avoid treating suspected STIs with antibiotics purchased without proper assessment.

Self-medication can:

• Delay correct diagnosis
• Use the wrong medicine
• Use an incorrect dose
• Temporarily hide symptoms
• Fail to cure the infection
• Increase antimicrobial resistance
• Cause adverse effects
• Leave sexual partners untreated
• Allow complications to develop

This is particularly important for gonorrhoea because antimicrobial resistance is reducing treatment options globally.

Partner Testing and Treatment

For several STIs, treating one person while leaving an infected sexual partner untreated creates a risk of reinfection.

People diagnosed with an STI may need advice about:

• Informing recent partners
• Partner testing
• Partner treatment
• Temporary sexual abstinence
• Condom use
• Repeat testing
• Follow-up care

Partner notification should be confidential, respectful and free from blame, coercion or violence.

How Can STIs Be Prevented?

No single method prevents every STI.

Combining several approaches provides stronger protection.

1. Use Condoms Correctly and Consistently

External and internal condoms can significantly reduce the risk of HIV and many other STIs when used correctly during vaginal, anal or oral sex.

Protection is less complete for infections transmitted through exposed genital skin, such as:

• HPV
• Herpes
• Syphilis when sores occur outside the covered area

2. Receive Recommended Vaccines

Vaccines are available against:

• Hepatitis B
• Important HPV types

HPV vaccination can prevent infection with important cancer-causing HPV types and, depending on the vaccine, types responsible for most genital warts.

Nigeria introduced HPV vaccination into its routine immunisation programme for eligible girls.

Vaccination prevents infection. It does not treat an HPV infection that has already been acquired.

3. Get Tested

Testing identifies infections that may otherwise remain unnoticed.

This can allow treatment before complications develop and reduce transmission to sexual partners.

4. Reduce Exposure to Multiple Sexual Partners

Having fewer sexual partners can reduce exposure risk, particularly when partners know their STI status and maintain mutually monogamous relationships.

5. Communicate With Sexual Partners

Useful conversations can include:

• Recent STI testing
• Known infections
• Condom use
• HPV and hepatitis B vaccination
• HIV prevention
• Current symptoms

Having these conversations should be approached as healthcare and risk reduction rather than blame.

6. Use HIV Prevention Services

People who do not have HIV but have ongoing exposure risk may benefit from pre-exposure prophylaxis, or PrEP.

Someone who has had a possible recent exposure may need PEP.

PEP should be started as soon as possible and no later than 72 hours after exposure.

7. Do Not Share Injecting Equipment

Never share:

• Needles
• Syringes
• Injecting equipment

This reduces the risk of HIV, hepatitis B, hepatitis C and other blood-borne infections.

8. Attend Antenatal Care Early

Pregnant women should register for antenatal care early and receive recommended screening.

Testing and treatment for HIV, syphilis, hepatitis B and other infections can prevent serious complications for both mother and baby.

9. Consider Voluntary Medical Male Circumcision

Voluntary medical male circumcision reduces the risk of heterosexual HIV acquisition in men and provides some protection against certain other sexually transmitted infections.

It does not provide complete protection and should be combined with other prevention methods.

STI Services Are More Than Testing and Treatment

In February 2026, WHO released its first consolidated operational handbook on sexually transmitted infections.

The guidance reflects an important shift in STI control.

Effective STI programmes should not operate as isolated services. Prevention, testing, diagnosis, treatment, partner management, surveillance and follow-up need to be connected.

WHO also emphasises integrating STI services with other parts of the health system, including:

• Primary healthcare
• HIV services
• Sexual and reproductive health services
• Antenatal care
• Community-based services

This matters because diagnosing an infection is only the beginning.

People must also be able to access appropriate treatment, partner services and follow-up without stigma, excessive cost or unnecessary barriers.

Possible Complications of Untreated STIs

Untreated STIs can cause serious health problems.

Possible complications include:

• Pelvic inflammatory disease
• Chronic pelvic pain
• Infertility
• Ectopic pregnancy
• Epididymitis
• Pregnancy complications
• Newborn infection
• Stillbirth
• Neurological complications of syphilis
• Cardiovascular complications of syphilis
• Chronic liver disease
• Cervical and other HPV-related cancers
• Increased susceptibility to HIV

Early diagnosis and treatment can prevent many of these outcomes.

STIs, Shame and Stigma

An STI diagnosis should not be treated as a moral judgement.

STIs are common health conditions.

Fear of embarrassment or discrimination can discourage people from:

• Testing
• Informing partners
• Seeking treatment
• Returning for follow-up
• Using HIV prevention services

Confidential, respectful and non-judgemental care makes STI prevention and treatment more effective.

When Should You Seek Medical Care?

Seek assessment if you develop:

• Genital sores, blisters or warts
• Unusual vaginal discharge
• Penile discharge
• Pain or burning during urination
• Pelvic or lower abdominal pain
• Testicular pain or swelling
• Bleeding after sex
• A new unexplained rash following possible sexual exposure
• Symptoms during pregnancy
• A sexual partner who has recently been diagnosed with an STI

Seek urgent medical care if you have:

• Possible HIV exposure within the previous 72 hours
• Severe pelvic or lower abdominal pain
• Fever with genital or pelvic symptoms
• Fainting
• Heavy abnormal bleeding
• Severe or sudden testicular pain

Common Myths About STIs

Myth: You can always tell when someone has an STI.

False. Many STIs cause no symptoms.

Myth: Only people with many sexual partners get STIs.

False. A single exposure to an infected partner can transmit an STI.

Myth: Toilet seats commonly transmit STIs.

False. STIs are not normally acquired from toilet seats or ordinary social contact.

Myth: Oral sex cannot transmit infections.

False. Several STIs can spread through oral sexual contact.

Myth: If symptoms disappear, the infection has gone.

False. Symptoms can improve even when an infection remains present.

Myth: Antibiotics bought from a pharmacy can treat any STI.

False. Different infections require different treatments, and unnecessary antibiotic use contributes to antimicrobial resistance.

Myth: HPV means cancer.

False. Most HPV infections do not cause cancer. Persistent infection with certain high-risk HPV types creates the major cancer risk.

Myth: Genital warts mean cervical cancer.

False. Most genital warts are caused by low-risk HPV types that are different from the types responsible for most cervical cancers.

Frequently Asked Questions

Can someone have an STI without symptoms?

Yes. Many STIs cause 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.

Can oral sex transmit an STI?

Yes. Oral sex can transmit infections including gonorrhoea, syphilis, herpes, chlamydia and HPV.

Can condoms prevent every STI?

No. Condoms substantially reduce the risk of many infections but do not completely cover all genital skin.

Are all STIs curable?

No.

Chlamydia, gonorrhoea, syphilis and trichomoniasis are generally curable when treated correctly.

HIV and genital herpes can be effectively managed but are not eliminated by routine treatment.

Can an STI come back after treatment?

A successfully treated infection can be acquired again if someone is re-exposed.

Should both partners receive treatment?

For several STIs, partners need evaluation and treatment. The recommendation depends on the infection.

Can untreated STIs cause infertility?

Yes.

Untreated chlamydia and gonorrhoea can cause pelvic inflammatory disease, which can damage the reproductive tract and contribute to infertility.

Does STI treatment cause infertility?

Correct treatment protects reproductive health. Untreated infections are a much greater threat to fertility than appropriately prescribed treatment.

When should I test after having unprotected sex?

The appropriate timing depends on the infection because different STIs have different testing windows.

A healthcare professional can advise which tests are appropriate immediately and which may need to be repeated later.

Possible HIV exposure within the previous 72 hours should be treated as urgent because PEP is time-sensitive.

Key Takeaways

Sexually transmitted infections are common and many cause no noticeable symptoms.

STIs can spread through vaginal, anal and oral sex, while some can also spread through blood or from mother to child.

Chlamydia, gonorrhoea, syphilis and trichomoniasis are curable with appropriate treatment.

HIV can be effectively controlled with antiretroviral treatment, and people who maintain an undetectable viral load do not sexually transmit HIV.

HPV vaccination and hepatitis B vaccination can prevent important sexually transmitted infections.

Condoms significantly reduce risk but do not provide complete protection against every STI.

Testing matters because symptoms alone cannot confirm whether someone has an infection.

Self-medication with antibiotics should be avoided, particularly as antimicrobial resistance threatens gonorrhoea treatment.

And STI care should be confidential and free from shame. Testing, treatment, partner care and prevention are healthcare services, not moral judgements.

Sources and Further Reading

1. World Health Organization. Sexually transmitted infections fact sheet. Updated September 2025.
   https://www.who.int/news-room/fact-sheets/detail/sexually-transmitted-infections-%28stis%29

2. World Health Organization. Sexually transmitted infections health topic.
   https://www.who.int/health-topics/sexually-transmitted-infections

3. United States Centers for Disease Control and Prevention. STI Treatment Guidelines.
   https://www.cdc.gov/std/treatment-guidelines/default.htm

4. United States Centers for Disease Control and Prevention. Getting Tested for STIs.
   https://www.cdc.gov/sti/testing/index.html

5. World Health Organization. Gonorrhoea fact sheet.
   https://www.who.int/news-room/fact-sheets/detail/gonorrhoea-%28neisseria-gonorrhoeae-infection%29