Medically Reviewed

Sexually Transmitted Infections (STIs)

Symptoms, Causes & Treatment

Everything you need to know about sexually transmitted infections: how they spread, what symptoms to look for, how they are diagnosed, and the treatments available.

Book My Consultation
Learn More
Licensed UK clinicians
Same-day prescriptions, where clinically appropriate
Delivered to your door within 24 hours
What our patients say
4.7 out of 5
Easy and efficient! … I am on the mend and so glad this service exists.
Pete Garvey
Excellent. Started to feel unwell and needed to see Dr before going on holiday. Couldn't get' GP appointment in time. I was 'seen' within 30mins of signing up. Just picked up a prescription. Very impressed with the Dr Victoria White.
Iann de Courcy
Fantastic service received from the gp service. Easy to book consultation… Would definitely use again :- )
Jay
Fantastic service. Easy to sign up and instructions were very clear. My doctor, Dr Shakil David Alam was amazing; listened to my issues, gave me in depth advice and really helped me out. Would definitely reuse - the speed of the service was impressive. Thank you Dr Shakil.
Babac Pashazadeh
I'm not someone who posts reviews regularly, but I have to say the process was super smooth. Booked a same day appointment with a clearly experienced and friendly doctor…
Yardie Grandmaster
Excellent service - quick, professional, and really convenient. The doctors are thorough and the whole process is smooth from start to finish. Highly recommend.
Mohammad Hassan
What our patients say
4.7 out of 5
Easy and efficient! … I am on the mend and so glad this service exists.
Pete Garvey
Excellent. Started to feel unwell and needed to see Dr before going on holiday. Couldn't get' GP appointment in time. I was 'seen' within 30mins of signing up. Just picked up a prescription. Very impressed with the Dr Victoria White.
Iann de Courcy
Fantastic service received from the gp service. Easy to book consultation… Would definitely use again :- )
Jay
Fantastic service. Easy to sign up and instructions were very clear. My doctor, Dr Shakil David Alam was amazing; listened to my issues, gave me in depth advice and really helped me out. Would definitely reuse - the speed of the service was impressive. Thank you Dr Shakil.
Babac Pashazadeh
I'm not someone who posts reviews regularly, but I have to say the process was super smooth. Booked a same day appointment with a clearly experienced and friendly doctor…
Yardie Grandmaster
Excellent service - quick, professional, and really convenient. The doctors are thorough and the whole process is smooth from start to finish. Highly recommend.
Mohammad Hassan
Overview

What Are STIs?

Sexually transmitted infections (STIs) are infections passed from one person to another through sexual contact -- vaginal, anal, or oral sex, and sometimes through close genital skin-to-skin contact. STIs are extremely common. In the UK, over 390,000 new STI diagnoses are made each year, and the true number of infections is significantly higher because many STIs cause no symptoms and go undiagnosed.

‍

STIs are caused by bacteria, viruses, or parasites. Some are easily curable with antibiotics (chlamydia, gonorrhoea, syphilis, trichomoniasis). Others are caused by viruses and cannot be cured but can be effectively managed with treatment (genital herpes, HPV, hepatitis B). Left untreated, STIs can lead to serious complications including pelvic inflammatory disease (PID), infertility, ectopic pregnancy, chronic pain, and -- in the case of syphilis -- life-threatening illness.

‍

STIs affect people of all ages, genders, and sexual orientations. They are not a reflection of personal hygiene, character, or lifestyle choices. The most effective tools for sexual health are regular testing, prompt treatment, open communication, and consistent condom use

Symptoms

What Are the Symptoms of STIs?

STI symptoms vary widely by infection. Many STIs cause no symptoms at all. The following are the most common presentations to be aware of.

STI Symptoms (Common)

Unusual discharge (penis, vagina, rectum) · Sores, blisters, or ulcers on genitals or mouth · Burning or pain when urinating · Rash on palms, soles, or trunk · Swollen lymph nodes in groin · Itching or irritation around genitals · Pelvic or testicular pain · Warts or growths on genitals

common
When STI Symptoms Are Urgent

Severe pelvic pain with fever (possible PID) · High fever with rash and joint pain (disseminated gonorrhoea) · Neurological symptoms (confusion, headache, stiff neck) with STI history — possible syphilitic meningitis · Inability to urinate due to urethral swelling

serious
When STI Symptoms Require Emergency Care

Seek emergency care if STI symptoms are accompanied by high fever and severe pelvic or abdominal pain (possible PID or systemic infection), neurological symptoms, or inability to urinate.

Causes & Risk Factors

What Causes STIs?

STIs are caused by bacteria, viruses, or parasites transmitted through sexual contact. Understanding how each infection spreads is the foundation of prevention and partner management.

Sexual Transmission Routes

STIs are transmitted through unprotected vaginal, anal, or oral sex. Some (herpes, HPV, syphilis) can spread through skin-to-skin contact even without penetration or visible symptoms.

Asymptomatic Nature of STIs

Many STIs, particularly chlamydia, gonorrhoea, and early HIV, cause no symptoms at all. Regular testing is the only way to detect them — waiting for symptoms means delayed treatment and onward transmission.

Complications of Untreated STIs

Untreated STIs can cause PID, infertility, ectopic pregnancy, epididymo-orchitis, and increased HIV transmission risk. Syphilis causes serious cardiovascular and neurological damage if untreated for years.

Intracellular Pathogen Mechanism

Chlamydia trachomatis infects columnar epithelial cells. It replicates intracellularly, causing a subclinical inflammatory response that silently damages the fallopian tubes and epididymis over time.

Condom Effectiveness & Limits

Condoms reduce STI transmission by 85–98% when used consistently and correctly. They are less effective for infections spread by skin contact (herpes, HPV, syphilis) where lesions extend beyond the condom-covered area.

STI Co-infection

STI co-infection is common. Gonorrhoea and chlamydia frequently co-exist (15–40% co-infection rate). HIV significantly increases susceptibility to all other STIs and their complications.

Key Risk Factors

Unprotected vaginal, anal, or oral sex
Multiple sexual partners
No regular STI testing
Previous STI diagnosis
Sex work involvement
Inconsistent condom use
New sexual partner
Sharing injecting equipment (HIV/Hep C)
Male sex with men (MSM)
Not on PrEP or ART (HIV)
Sub-Saharan African origin (HIV endemic)
Known HIV-positive partner without ART suppression
Diagnosis

How Are STIs Diagnosed?

A full STI screen includes urine, swabs (genital, rectal, pharyngeal), and blood tests. The specific tests depend on your sexual practices and symptoms. Results are typically available within 1–2 weeks. Self-sampling kits are available online from NHS services.

Test
What It Detects
When Used
Full STI Screen (Urine + Swabs + Blood)
Chlamydia, gonorrhoea, syphilis, HIV, Hep B, Hep C from one visit
Annual screen for all sexually active people; after unprotected sex
NAAT (Nucleic Acid Amplification Test)
Chlamydia and gonorrhoea DNA; most sensitive test available
First-line test for all chlamydia and gonorrhoea screening
Syphilis Serology (TPPA, RPR, VDRL)
Treponemal and non-treponemal syphilis antibodies; stage and activity
Suspected syphilis; annual STI screen; all HIV-positive patients; pregnancy
HIV Antigen/Antibody Combination Test (4th Gen)
HIV p24 antigen from 10 days; HIV antibodies from 28 days
All STI screens; HIV testing after possible exposure
Hepatitis B Surface Antigen & Antibody Panel
Active Hep B infection, immunity status, and need for vaccination
Annual screen in MSM and PWID; all new HIV diagnoses
Gonorrhoea Culture & Sensitivity
Specific antibiotic sensitivities of gonorrhoea organism; resistance patterns
Confirmed gonorrhoea; treatment failure; suspected antibiotic resistance
Treatment Options

How Are STIs Treated?

Treatment depends on the specific STI. Bacterial infections are cured with antibiotics; viral infections are managed with antivirals or antiretrovirals. All treatments require partner notification.

Antibiotic
Typical Use
Standard Course
Azithromycin 1g + Ceftriaxone 1g IM (STI Dual Therapy)
Confirmed gonorrhoea (ceftriaxone) + presumptive chlamydia co-treatment (azithromycin)
Single day treatment; contact tracing and test of cure for gonorrhoea at 2 weeks
Doxycycline (Chlamydia / Syphilis)
First-line chlamydia treatment; alternative to penicillin for syphilis
100mg twice daily for 7 days (chlamydia); 14–28 days (syphilis latent)
Penicillin G (Benzathine) IM (Syphilis)
Gold-standard syphilis treatment at all stages; only option in pregnancy
Primary/secondary: single 2.4 MU IM; late: 3 weekly doses
Antiretroviral Therapy (ART / HAART)
All HIV-positive individuals regardless of CD4 count; suppresses viral load to undetectable
Daily; lifelong; typically single-tablet regimen
PEP (Post-Exposure Prophylaxis)
HIV prevention after known or likely HIV exposure (unprotected sex, needlestick)
28-day course started within 72 hours of exposure
PrEP (Pre-Exposure Prophylaxis)
HIV prevention in high-risk individuals (MSM, discordant partners, PWID)
Daily or on-demand (2-1-1 protocol); ongoing

Supportive Measures

Complete the full antibiotic course even if symptoms resolve early. Abstain from sex until you and all notified partners have completed treatment. Attend test of cure for gonorrhoea. Inform recent sexual partners — clinics can do this anonymously on your behalf.

Recurrent or Persistent STIs

Some STIs recur or persist: herpes reactivates lifelong; HPV may persist for years; gonorrhoea can be reinfected immediately after treatment; chlamydia risk persists with new partners. Developing a regular testing habit and consistent condom use with new partners is the foundation of long-term sexual health.

When to Seek Help

When Should You Get Tested?

Seek Emergency Care (999 / A&E) If:

Severe pelvic pain with fever (possible PID) · Testicular pain with fever (possible epididymo-orchitis) · Neurological symptoms with known STI history · Suspected meningitis in a person with secondary syphilis — call 999.

See a Clinician the Same Day If:

You have had unprotected sex · A partner has been diagnosed with an STI · You have symptoms of an STI · You have not been tested in the past year and are sexually active · You want to start PrEP or discuss HIV prevention.

Prevention

How to Prevent STIs

Most STIs are preventable. Consistent testing, condom use, and vaccination are the cornerstones of sexual health protection.

Test Annually (or More Often)

Annual STI testing is recommended for all sexually active people. Those with multiple partners should test every 3 months. Free NHS testing is available at sexual health clinics, online via SHGM/SH:24, and from GP surgeries.

Use Condoms Consistently

Use condoms consistently for vaginal, anal, and oral sex with new or casual partners. Dental dams reduce transmission during oral-vulval contact. Lube reduces condom breakage and anal mucosal trauma.

Partner Notification Is Essential

Notify all recent sexual partners when diagnosed with an STI so they can be tested and treated. Partner notification can be done directly or anonymously through the sexual health clinic (contact tracing service).

Vaccines: HPV & Hepatitis B

HPV vaccination prevents 90% of cervical cancer and most genital warts. Hepatitis B vaccine is recommended for all MSM, PWID, and sexual health clinic attendees not previously vaccinated.

PrEP for High-Risk Individuals

PrEP (Truvada or Descovy) is available free on the NHS at sexual health clinics for eligible high-risk individuals. It is over 99% effective when taken as prescribed. Regular HIV and kidney function testing is required during use.

U=U: Undetectable = Untransmittable

If you are HIV-positive and on effective ART with an undetectable viral load, you cannot transmit HIV to sexual partners (U=U — Undetectable = Untransmittable). This is one of the most important advances in HIV medicine.

Getting Treatment

Speak to a Clinician About STIs

Through The GP Service, you can access confidential STI assessment, testing referrals, and antibiotic prescriptions for treatable infections — discreetly and without a waiting room.

Woman sitting on a couch using a mobile app with a calendar and timer interface on the screen.
1
Book Your Appointment
Book to see a consultant online the same day, at a time that suits you.
Open 365 days a year, 8am - 5pm
Same-day appointments available
Smiling male doctor wearing a white coat and stethoscope holding a tablet in a hospital corridor.
2
See a Consultant
Speak to one of our licensed medical professionals from anywhere - using a phone, computer, or tablet.
Request prescriptions
Request Fit Notes
Request Referral Letters
Pharmacist wearing a white coat smiling and explaining medication to a female customer in a pharmacy.
3
Book a Consultation
Within minutes of your consultation, receive prescriptions, fit notes, or referral letters where clinically appropriate.
Collect prescriptions within an hour of issue
Pick up from ANY pharmacy
Shared with your medical records & NHS GP

Expert clinical advice, when you need it.

See a licensed clinician online in minutes. If treatment is clinically right for you, your prescription will be sent to your pharmacy the same day.
Book My Consultation
No waiting room
Delivered to your door within 24 hours
Open 365 days a year
Licensed UK clinicians
Secure & confidential
Frequently Asked Questions

STI FAQs

How often should I get tested for STIs?

STI testing is recommended annually for all sexually active people. Those with new or multiple partners should test every 3 months. Testing is free at NHS sexual health clinics and from online services (SH:24, SHGM). You do not need symptoms to be tested — most STIs cause no symptoms. A full STI screen covers chlamydia, gonorrhoea, syphilis, HIV, hepatitis B, and hepatitis C. Specific sites tested (urine, swabs, blood) depend on your sexual practices. Results are usually available within 1–2 weeks. Positive results trigger automatic partner notification advice.

Can STIs be cured?

Not all STIs are curable, but all are treatable. Bacterial STIs — chlamydia, gonorrhoea, and syphilis — are fully curable with antibiotics when diagnosed promptly. Viral STIs — HIV, herpes, HPV, and hepatitis B — cannot be cured but can be effectively managed. HIV is controlled with ART to the point of undetectability. Herpes is managed with antivirals that suppress outbreaks. HPV often clears naturally within 1–2 years in people with healthy immune systems. Genital warts can be treated and removed, though the underlying HPV virus may persist. The key message: all STIs are manageable with prompt diagnosis and treatment.

What happens if chlamydia is left untreated?

Without treatment, chlamydia can persist silently for months or years, causing progressive damage to the reproductive tract. In women, untreated chlamydia causes pelvic inflammatory disease (PID) in 10–15% of cases, leading to tubal factor infertility, chronic pelvic pain, and ectopic pregnancy risk increased 6–10-fold. In men, chlamydia causes epididymo-orchitis, which can impair sperm production and quality. Reactive arthritis (formerly Reiter's syndrome) — involving joint inflammation, eye inflammation, and urethritis — is a rare but recognised complication. These complications are entirely preventable with prompt diagnosis and a simple 7-day course of doxycycline.

Is gonorrhoea still treatable?

Gonorrhoea is increasingly difficult to treat due to rising antibiotic resistance. The current UK first-line treatment is a single intramuscular injection of ceftriaxone 1g. A test of cure is required 2 weeks later to confirm eradication. Azithromycin is no longer recommended routinely due to resistance. Multidrug-resistant gonorrhoea has been identified in multiple countries, including the UK. If you have been treated for gonorrhoea and symptoms persist, return to the clinic immediately — do not take additional antibiotics without guidance. Treatment of all recent sexual partners is essential to prevent reinfection.

Is HPV vaccination still worth having if I'm already sexually active?

HPV vaccination is highly effective before first sexual contact but still provides meaningful protection after sexual debut. The NHS offers Gardasil 9 to all children aged 12–13 regardless of gender. Catch-up vaccination is available free up to age 25 for women and men who have not been vaccinated. MSM can receive free vaccination at sexual health clinics up to age 45. For people already exposed to HPV, the vaccine still protects against strains they have not yet encountered. HPV vaccination combined with regular cervical screening has the potential to virtually eliminate cervical cancer in the UK.

Can you live a normal life with HIV?

Yes. HIV is now a manageable chronic condition, not a death sentence. With antiretroviral therapy (ART), people with HIV can live long, healthy lives with a normal life expectancy. ART suppresses the virus to undetectable levels in the blood, meaning it cannot be transmitted sexually (Undetectable = Untransmittable, or U=U). Most people on modern ART take a single tablet daily and experience minimal side effects. HIV does not prevent you from having children, working, or having a fulfilling life. In the UK, HIV care is excellent and free on the NHS. The biggest barrier to good outcomes is late diagnosis — testing early is life-saving.

What is PEP and how do I get it?

PEP (post-exposure prophylaxis) is a 28-day course of antiretroviral drugs that prevents HIV infection after a potential exposure. It must be started within 72 hours — the sooner the better. PEP is available from A&E departments, sexual health clinics, and some GUM clinics 24/7. It is free on the NHS for NHS patients. PEP is not a substitute for PrEP or condoms and should be used only in genuine emergencies (unprotected sex with a known HIV-positive person not on suppressive ART, condom failure, sexual assault, or needlestick). After completing PEP, an HIV test at 45 days and 3 months confirms whether infection was prevented.

Is PE treatable?

PE affects approximately 20–30% of men at some point — making it the most common male sexual dysfunction. Many men suffer in silence due to embarrassment, assuming it is shameful or untreatable. In reality, PE is a well-recognised medical condition with highly effective treatments. Dapoxetine (a short-acting SSRI licensed specifically for PE) can more than triple ejaculatory latency time in clinical trials. Behavioural techniques (stop-start, squeeze) are effective for lifelong PE. Combining medication with psychological or couples therapy produces the best outcomes. Most men with PE who seek treatment experience significant improvement.

Medical Disclaimer: The information on this page is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare professional with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay seeking it because of something you have read on this page. If you think you may have a medical emergency, call 999 or your local emergency services immediately.