What syphilis is and how it spreads
Syphilis is a bacterial sexually transmitted infection (STI) caused by Treponema pallidum. It spreads through close skin-to-skin contact during vaginal, anal or oral sex with someone who has it, usually through contact with a sore, and can also pass from a pregnant woman to her baby. It cannot be caught from toilet seats, shared cups or casual contact.
Syphilis used to be rare in the UK, but it has become steadily more common again over the last two decades. Anyone who is sexually active without consistent condom use can be at risk, and it affects people of all ages, genders and backgrounds, although some groups are disproportionately affected.
What makes syphilis tricky is that it moves through distinct stages, and the symptoms at each stage can be mild, easy to dismiss, or absent altogether, even while the infection remains active and able to be passed on.
Why syphilis cases are rising in the UK
UK Health Security Agency (UKHSA) data shows that syphilis diagnoses in England reached 13,030 in 2024, up 5% from 12,456 the year before, the highest annual total since the 1940s. Early-stage diagnoses, which reflect genuinely new infections rather than older cases picked up on screening, rose by 2%, from 9,375 to 9,535.
Gay, bisexual and other men who have sex with men remain the group most affected, but UKHSA figures also show rising diagnoses among heterosexual men and women. In response, UKHSA has published a response plan focused on expanding testing and reducing missed diagnoses, since syphilis is straightforward to treat once it is actually identified.
None of this means syphilis is common for any one individual, but it does mean that if you have symptoms, a new or casual partner, or a partner who has been diagnosed with an STI, testing is a sensible and widely available step rather than something to put off.
Symptoms by stage: primary, secondary, latent and late
Syphilis symptoms change as the infection progresses, and they can fade on their own even without treatment, which does not mean the infection has gone away. The table below sets out what tends to happen at each stage.
Because the early sore is painless and often hidden from view, and because later symptoms can be mistaken for a minor rash or a passing flu-like illness, many people with syphilis do not realise they have it. Secondary-stage syphilis can also cause wart-like growths in warm, moist areas and white patches inside the mouth, alongside the more commonly described rash, which adds to how easily it can be confused with something else entirely. This is exactly why testing, rather than waiting for symptoms to confirm themselves, is the reliable way to know.
Getting tested for syphilis in the UK
Testing for syphilis is free on the NHS and widely available. Sexual health clinics and some GP surgeries can test using a blood sample, and a swab may also be taken directly from a sore if one is present. Many areas also offer postal home-testing kits, where you take a small blood sample yourself and send it to a laboratory, with results usually available within a few days.
It is worth getting tested if you have any symptoms that could fit, if a partner has been diagnosed with an STI, or as part of a routine sexual health check after a new or casual partner, even without symptoms, given how often early syphilis goes unnoticed. A full sexual health screen will usually test for syphilis alongside other common infections, including HIV, since several STIs can occur at the same time and some share similar risk factors.
One practical point about timing: blood tests for syphilis can take a few weeks to turn positive after exposure, so a test taken very soon after a risk may need repeating later to be fully reliable. A clinician or the testing service can advise on the right timing for your situation, and on whether a swab from a visible sore would give a faster answer than waiting for the blood test window to pass.
Pregnant women in the UK are routinely offered syphilis screening as part of antenatal blood tests, because untreated syphilis can pass to an unborn baby with serious consequences. UKHSA recorded 13 cases of congenital syphilis in 2023, the most recent complete year reported, which is one of the reasons antenatal screening and prompt treatment in pregnancy are taken so seriously.
How syphilis is treated
Syphilis is curable with antibiotics at every stage, although earlier treatment is simpler and avoids any risk of long-term complications. The standard first-line treatment for early-stage syphilis is a single intramuscular injection of a long-acting penicillin, usually given in the buttock. Later-stage or longer-standing infections typically need a longer course of injections over a few weeks, decided by the treating clinician based on how long the infection has likely been present.
For people who are allergic to penicillin, doxycycline tablets taken over two to four weeks are a recognised alternative, though penicillin remains preferred where it can be safely used, including in pregnancy.
Important safety information
Some people feel feverish or unwell for a day or so after the injection, which usually settles on its own and is not a sign that treatment has failed. You will usually be asked to return for a blood test at 6 and 12 weeks after treatment to confirm the infection has cleared, since the antibody levels measured in the blood fall gradually rather than disappearing overnight.
Partners, follow-up testing and when to seek care
Anyone you have had sex with in the period before your diagnosis, which can stretch back several months depending on how long you have likely had the infection, should also be tested, even if they have no symptoms. Sexual health clinics can usually help contact partners discreetly, including on your behalf if you would rather not do it yourself.
It is best to avoid any sexual contact until treatment is finished and, where follow-up testing is recommended, your results confirm the infection has cleared. This protects partners and reduces the small chance of reinfection from someone who has not yet been treated.
Having syphilis once and being treated successfully does not make you immune. Because the infection is passed on through contact rather than producing lasting protection, it is entirely possible to catch it again from a different, or the same, untreated partner in future. This is one more reason why consistent condom use and regular testing after new or casual partners remain worthwhile even once a past infection has been cleared.
Speak to a GP or sexual health clinic promptly if you notice a new sore, rash or swollen glands that could fit the picture above, if a partner tells you they have an STI, or if you are pregnant and have any risk of exposure, since untreated syphilis in pregnancy can seriously affect the baby. Your clinician will advise on testing and treatment based on your individual circumstances.