Can an STI come back after treatment?

Yes, an STI can seem to come back after treatment. There are four main reasons:

• Reinfection: you catch the same infection again, from a partner who hasn’t been treated or from a new partner.
• Treatment that didn’t work: for example, if the tablets weren’t taken as prescribed, or the bacteria are resistant to the antibiotic.
• An infection that stays in the body: Herpes and genital warts can come back without a new infection.
• Symptoms from something else: another untreated infection can cause similar symptoms.

Treatment works for most people, so when a bacterial STI comes back, it’s usually a new infection.

Having an STI doesn’t protect you from catching it again. UK guidelines say Chlamydia gives only limited immunity, and Syphilis gives none. Reinfection is common: about 10% to 15% of young adults diagnosed with Chlamydia test positive again at their next test.

To avoid passing the infection back and forth, your partners need testing and treatment too, and you need to wait before having sex again. The waiting time depends on the infection:

• Chlamydia: until you and your partner have finished treatment, and your symptoms have gone
• Gonorrhoea: until 7 days after you and your partners have finished treatment
• Syphilis: until 2 weeks after you and your partner have finished treatment
• Trichomonas: until at least 1 week after you and your partners have finished treatment
• Mycoplasma genitalium: until 14 days after you started treatment, and your symptoms have gone

Read more in “Can you tell a partner anonymously they need an STI test?”

Treatment for most STIs works well. For example, UK guidelines report no cases of treatment failure when a genital Gonorrhoea infection that responds to ceftriaxone has been treated with a ceftriaxone injection.

Treatment can fail, though, if tablets aren’t taken as prescribed, or if the bacteria are resistant to the antibiotic. Resistance is growing for some STIs:

• Gonorrhoea: cases resistant to ceftriaxone, the main treatment, are rising in England. There were 15 in the first 8 months of 2025, more than the 13 in all of 2024. Most were linked to travel to or from the Asia-Pacific region.
• Mycoplasma genitalium: in 2025, about two thirds of samples tested in England were resistant to azithromycin, and one in five to moxifloxacin. Doctors now choose treatment based on resistance testing.

Take any antibiotics exactly as prescribed. Using antibiotics when you don’t need them can also mean they won’t work for you in the future. Read more in “Is Mycoplasma genitalium gaining antibiotic resistance?”

Some STIs stay in your body after the first infection:

• Herpes: once you have the virus, it stays in your body, and outbreaks can come back. They’re usually milder than the first one and tend to happen less often over time. Triggers can include stress, friction, being unwell and too much sun on the area. If you have more than 6 outbreaks a year, daily antiviral medicine may help.
• HPV and genital warts: treatment can take weeks or months, and warts may come back. Most HPV infections clear within 2 years, but the same type of HPV is found again in at least 10% to 20% of women who seemed to have cleared it, possibly because it was still there at levels too low for tests to find.
• HIV: there’s no cure, but daily treatment keeps the virus under control. Someone on effective treatment with an undetectable viral load can’t pass HIV on.

Syphilis is different. Antibiotics cure it, and blood tests at 3, 6 and 12 months check the treatment has worked. One type of Syphilis blood test usually stays positive for life, even after successful treatment, so a positive result on its own doesn’t mean the infection is back.

Read more in “How long does a Herpes outbreak last?”

Symptoms that don’t go away after treatment should be checked. They don’t always mean the infection is still there, but they can.

For example, in men treated for urethritis (inflammation of the tube that carries pee), symptoms continue or come back in 5% to 25%. Causes include Mycoplasma genitalium, Chlamydia, reinfection and missed doses, although often no infection is found.

UK guidelines advise going back to be checked if you still have symptoms 2 weeks after starting treatment. A test of cure is also recommended for Chlamydia or Gonorrhoea if your symptoms don’t go away.

Whether you need another test, and when, depends on the infection:

• Chlamydia: a test of cure isn’t usually needed. It’s recommended in pregnancy, if the tablets may not have been taken properly, or if symptoms don’t go away, at least 3 weeks after finishing treatment. If you’re under 25, test again 2 to 6 months after treatment.
• Gonorrhoea: a test of cure is recommended at least 2 weeks after treatment if the infection was in your throat, your symptoms don’t go away, you’re pregnant, you were treated with something other than ceftriaxone, or the lab couldn’t check which antibiotics work.
• Syphilis: blood tests at 3, 6 and 12 months after treatment.
• Trichomonas: a test of cure only if symptoms don’t go away or come back, ideally 4 weeks after starting treatment.
• Mycoplasma genitalium: no test of cure is needed if your symptoms clear up.

Don’t test too soon. Dead Chlamydia bacteria can still show up on a test for 3 to 5 weeks after treatment. Read more in “How long will I test positive for an STI after treatment?”

If you’ve had a new partner since your treatment, or it’s time for a routine check, Better2Know offers:

• Full Screen: tests for 7 infections, including Chlamydia, Gonorrhoea, HIV, Syphilis and Mycoplasma, from 28 days after sex, with results in 3 days (5 days for the home test). If you test before 45 days, a negative HIV result needs a repeat test. You can book it at one of our clinics or order a Full Screen home test.
• Peace of Mind: checks for Chlamydia, Gonorrhoea and Syphilis from 14 days after sex, with results in 2 days.
• Platinum Screen: our most comprehensive STI screen. It tests for 12 infections, adding Hepatitis C, Herpes 1, Herpes 2, Trichomonas and Gardnerella to the Full Screen, from 28 days after sex, with results in 3 days. If you test before 45 days, a negative HIV result needs a repeat test.

All three include a Syphilis test. A Syphilis test in the first 3 months after sex can miss the infection, so you may need a repeat test. If you’re checking that Chlamydia treatment worked, wait at least 3 weeks after finishing it. Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

Can Chlamydia come back on its own?

No. If Chlamydia comes back, it’s usually a new infection, or treatment that didn’t work, for example because the tablets weren’t all taken. Read more in “Can Chlamydia go away on its own?”

Why do I still test positive after treatment?

Tests can pick up dead bacteria for a few weeks after treatment, which is why a test of cure for Chlamydia should wait at least 3 weeks. For Syphilis, one type of blood test usually stays positive for life, even after the infection has been cured.

Can you get HPV again?

Yes. You can catch a different type of HPV, and the same type can sometimes be found again after it seemed to have cleared. Read more in “Can I get reinfected with HPV?”

An STI can come back after treatment, but it’s usually a new infection rather than the old one returning. Make sure your partners are treated, wait the right amount of time before having sex, and test again if you have a new partner or your symptoms don’t go away. Herpes and genital warts can come back without a new infection, and treatment can help.

Book a Full Screen at a clinic near you or order a home test kit from 28 days after sex. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 1 September 2023 and was last updated on 30 September 2026.

Medical review. This article was medically reviewed by Dr Steve Chapman, Doctor with a wealth of clinical experience in the field of STIs, on 4 March 2025. It is general information and not a substitute for personal medical advice.

Sources

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