The essentials

Syphilis is a bacterial sexually transmitted infection that antibiotics cure, but if it is missed it can harm the brain, eyes, heart and an unborn baby. It often starts with a painless sore that heals on its own. Diagnosis needs two kinds of blood test read together: a treponemal test and a nontreponemal test such as the RPR. See a doctor soon for a new sore or a rash on the palms or soles; get emergency care for sudden loss of vision or hearing.

What is syphilis, at a glance?

Syphilis is caused by the bacterium Treponema pallidum. It spreads through direct contact with a syphilis sore during vaginal, anal or oral sex, and from a pregnant person to the baby, but not through toilet seats or swimming pools[1].

  • Worldwide: about 8 million adults aged 15 to 49 acquired syphilis in 2022[7].
  • United States: 190,242 cases of all stages in 2024 (provisional), 9.1% fewer than in 2023; congenital syphilis rose for the 12th year in a row, to 3,941 cases[6].
  • Key tests and treatment: treponemal antibodies plus an RPR or VDRL titer; penicillin injections chosen by stage[2].

What are the symptoms of syphilis at each stage?

Untreated syphilis moves through stages. The signs of the first two fade on their own, which is why it is easy to miss[1].

  • Primary. One or more firm, usually painless sores (chancres) where the bacteria entered: genitals, anus, rectum, lips or mouth[1]. The sore appears 10 to 90 days after exposure[12] and lasts 3 to 6 weeks[1].
  • Secondary. A rash, often on the palms or soles, that usually does not itch, with fever, swollen glands, sore throat, patchy hair loss and tiredness[1].
  • Latent. No signs, but the bacteria stay for years[1]. It is "early latent" when infection happened within the past year[2].
  • Tertiary. Uncommon, 10 to 30 years later, with damage to the heart, blood vessels, brain and nerves that can be fatal[1].

At any stage, it can reach the nervous system (severe headache, weakness, dementia), the eyes (pain, redness, vision loss) or the ears (hearing loss, ringing in the ears, dizziness)[1].

When should I see a doctor?

When to see a doctor

  • Emergency: call 911 for sudden loss of vision or hearing, a severe headache with confusion, weakness or a seizure: syphilis can affect the eyes, ears and nervous system[1].
  • Within 24 to 48 hours for a new genital, anal or mouth sore, even a painless one, a rash on the palms or soles, a partner diagnosed with syphilis, or a positive test in pregnancy[1][2].
  • At your next appointment for screening if you are at increased risk, take HIV PrEP or plan a pregnancy[1][9].

What causes syphilis, and who is at risk?

Sores can hide in the vagina, rectum or mouth, so a partner may not know they are infected. Having had syphilis does not protect you: you can catch it again[1].

  • Common Men who have sex with men, people with HIV and people taking PrEP, for whom regular testing is recommended[1].
  • Common Condomless sex or a partner who tested positive; condoms lower the risk but may not cover every sore[1].
  • Possible A bacterial STI such as chlamydia or gonorrhea in the past 12 months, the criterion CDC uses to offer doxycycline prevention[10].
  • Rare Infection from the mother during pregnancy, which can cause stillbirth, preterm birth or serious problems in the newborn[1].

How is syphilis diagnosed, and how do I read the blood tests?

Most diagnoses rest on a blood test; fluid from a sore is sometimes tested too[1]. No fasting is needed[11]. One test alone is not enough: a presumptive diagnosis needs two types[2].

  • Treponemal tests (EIA, CIA, TP-PA, FTA-ABS) detect antibodies against the bacterium itself and usually stay reactive for life[2].
  • Nontreponemal tests (RPR, VDRL) are not specific to syphilis; their titer rises with active infection and falls after treatment[2].

Together they separate an untreated infection from a past, treated one[8]. Some labs start with an automated treponemal test, then a quantitative RPR (the "reverse" order); others start with the RPR[2]. Here is a fictitious report in the reverse order.

Fictitious example of a syphilis serology report (United States format)
TestResultReference rangeFlag
Treponema pallidum antibody, total (CIA)ReactiveNonreactiveA
RPR (rapid plasma reagin)ReactiveNonreactiveA
RPR titer1:32NonreactiveA
HIV-1/2 antigen/antibodyNonreactiveNonreactive
  1. Treponemal antibody: reactive means syphilis at some point, now or in the past[11].
  2. RPR reactive: with line 1, this fits an infection needing treatment, unless you were treated before and older titers can be compared[2].
  3. Titer 1:32: the highest dilution of your blood that still reacts, the number used to follow treatment[2].
  4. HIV: everyone with primary or secondary syphilis should be tested[3]; see our HIV test results guide.

Reactive, nonreactive, 1:32: BloodSense reads your whole report line by line, in plain language, so you know what to ask at your appointment.

Explain my report
Reading the two tests together
TreponemalRPR or VDRLUsual meaning
ReactiveReactiveCurrent infection, or a past one whose titer has not fallen yet[2].
ReactiveNonreactiveA second treponemal test decides: reactive points to past or untreated infection, nonreactive to a false-positive screen[2].
NonreactiveReactiveOften a false-positive RPR, seen with HIV, autoimmune disease such as lupus, vaccination, drug injection, pregnancy or older age[2].
NonreactiveNonreactiveNo sign of syphilis, unless exposure was very recent: antibodies take a few weeks to appear[11].

Compare titers only on the same test (RPR with RPR). A fourfold change, two dilution steps such as 1:32 to 1:8, is what counts[2]. A spinal fluid test may be added if the nervous system is involved[2]. The single test is detailed in our RPR blood test guide, and our STI testing guide lists the infections usually checked at the same time.

How is syphilis monitored after treatment?

A cure is checked with the RPR or VDRL titer, not with the treponemal test, which usually stays reactive[2].

  • Primary or secondary syphilis: checks at 6 and 12 months[3].
  • Latent syphilis: titers at 6, 12 and 24 months, compared with the day of treatment[4].
  • Symptoms that return or a fourfold rise in titer suggest reinfection or treatment failure[3].
  • A slow fall is not always failure: 10% to 20% of people treated for primary or secondary syphilis do not reach a fourfold drop within 12 months[3].

How is syphilis treated?

Injected penicillin G is the preferred treatment at every stage; your clinician sets the dose[2].

  • Primary, secondary, early latent: one intramuscular injection of benzathine penicillin G[3][4].
  • Late latent or unknown duration: three injections, one week apart[4].
  • Penicillin allergy: for early syphilis, 14 days of doxycycline by mouth; azithromycin should not be used[3].
  • Pregnancy: only penicillin has proven effect; people with an allergy are desensitized, then treated[2].

Within 24 hours of the first injection, fever, headache and aches can occur: the Jarisch-Herxheimer reaction, which is not a penicillin allergy[2]. Antibiotics cure the infection but may not reverse damage already done[1]. Partners exposed within 90 days before a diagnosis of early syphilis should be treated even with a negative test[2], and no sex until everyone is treated and cured[12].

How can I prevent syphilis and protect a pregnancy?

  • Use condoms correctly every time[1].
  • Get screened if you are at increased risk, an "A" recommendation of the US Preventive Services Task Force[9].
  • Men who have sex with men and transgender women with a bacterial STI in the past 12 months can ask about doxy-PEP: doxycycline taken within 72 hours after sex cut syphilis by more than 70% in trials[10].
  • In pregnancy, test at the first visit, and at 28 weeks and delivery if at risk or in a high-rate area[5]. Untreated, it harms the pregnancy in 50% to 80% of cases[7].

Questions to ask your doctor

  1. Which stage do my results point to?
  2. Which tests were done, and what is my titer?
  3. How many injections do I need, and when are my follow-up tests?
  4. Which partners should be tested and treated?
  5. Do I need HIV and other STI tests, or an eye or hearing check?

Frequently asked questions

Is syphilis curable?

Yes, at any stage, although antibiotics cannot undo organ damage already done[1].

Why is my treponemal test still positive after treatment?

This antibody usually stays for life and does not show activity; the RPR or VDRL titer is followed instead[2].

Can I have syphilis with a negative test?

Yes, very early: antibodies take a few weeks to form, so a repeat test may be needed[11].

Is syphilis linked to HIV?

They spread the same way, so testing for one means testing for the other[3]. Late HIV is covered in our AIDS article.

  1. CDC. About Syphilis. 2025. cdc.gov (accessed October 31, 2026)
  2. CDC. Syphilis. STI Treatment Guidelines, 2021. cdc.gov (accessed October 31, 2026)
  3. CDC. Primary and Secondary Syphilis. STI Treatment Guidelines, 2021. cdc.gov (accessed October 31, 2026)
  4. CDC. Latent Syphilis. STI Treatment Guidelines, 2021. cdc.gov (accessed October 31, 2026)
  5. CDC. Syphilis During Pregnancy. STI Treatment Guidelines, 2021. cdc.gov (accessed October 31, 2026)
  6. CDC. Sexually Transmitted Infections Surveillance, 2024 (provisional). 2025. cdc.gov (accessed October 31, 2026)
  7. World Health Organization. Syphilis. Fact sheet, 2025. who.int (accessed October 31, 2026)
  8. Papp JR, Park IU, Fakile Y, et al. CDC Laboratory Recommendations for Syphilis Testing, United States, 2024. MMWR Recomm Rep. 2024;73(1):1-32. doi:10.15585/mmwr.rr7301a1 (accessed October 31, 2026)
  9. US Preventive Services Task Force. Screening for Syphilis Infection in Nonpregnant Adolescents and Adults. JAMA. 2022;328(12):1243-1249. doi:10.1001/jama.2022.15322 (accessed October 31, 2026)
  10. Bachmann LH, Barbee LA, Chan P, et al. CDC Clinical Guidelines on the Use of Doxycycline Postexposure Prophylaxis for Bacterial STI Prevention, 2024. MMWR Recomm Rep. 2024;73(2):1-8. doi:10.15585/mmwr.rr7302a1 (accessed October 31, 2026)
  11. MedlinePlus. Syphilis Tests. medlineplus.gov (accessed October 31, 2026)
  12. American Sexual Health Association. Understanding Syphilis and How to Prevent It. ashasexualhealth.org (accessed October 31, 2026)
  13. CDC. Get Tested. gettested.cdc.gov (accessed October 31, 2026)
  14. HealthCare.gov. Preventive care benefits for adults. healthcare.gov (accessed October 31, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.