Syphilis is a curable bacterial infection caused by Treponema pallidum, spread mainly through sexual contact with an infectious sore and from a pregnant person to their baby. It moves through four stages — primary, secondary, latent, and tertiary — often without symptoms in between, and it's treated with penicillin at every stage CDC, About Syphilis.
~3 wks; 10–90 days
by stage
| Item | Value |
|---|---|
| Primary sore | painless — ~3 wks; 10–90 days |
| Testing | 2 blood tests |
| Treatment | penicillin — by stage |
| Symptoms fade | ≠ cured |
What is syphilis?
Syphilis is an infection caused by a corkscrew-shaped bacterium called Treponema pallidum. Once it enters the body through a break in the skin or a mucous membrane, it multiplies locally and then spreads through the bloodstream, so an untreated infection can eventually reach the heart, brain, eyes, and nerves. The bacterium is fragile outside the body and passes almost entirely through close, direct contact. You won't get it from a toilet seat or a shared utensil.
Syphilis has a staged, on-and-off natural history. The earliest signs heal on their own, the body goes quiet for months or years, and the infection can resurface as serious organ damage long after the person assumed it was gone. That deceptive course earned it the nickname "the great imitator," and it keeps getting missed. Penicillin cures it, and the same drug has worked for decades.
Syphilis is also climbing in the United States. There were roughly 53,000 primary-and-secondary cases in 2023, and the late or unknown-duration stage rose from about 14 to nearly 30 per 100,000 between 2020 and 2023 CDC AtlasPlus, 2023. Rates vary widely. South Dakota, Washington DC, New Mexico, and Mississippi reported the highest primary-and-secondary rates in 2023, several times the national average.
Symptoms — and the silent reality
Syphilis symptoms track its four stages, but the silence between them is what trips people up. Symptoms fading is not the same as being cured. As the CDC puts it: the symptoms will go away whether or not you're treated, and without the right treatment the infection simply moves deeper.
Primary stage
The primary stage announces itself with one or more chancres — firm, round, painless sores at the spot where the bacterium entered: the penis, vagina, anus, rectum, lips, or mouth. Because the sore doesn't hurt and is often tucked inside the vagina, anus, or mouth, many people never notice it. A chancre typically appears about three weeks after exposure (the range is 10 to 90 days) and heals on its own over three to six weeks. That healing feels like recovery, but the infection is moving inward, and this is one of the main reasons syphilis is caught late.
Secondary stage
As the bacteria spread through the bloodstream, the secondary stage often brings a rough, red or reddish-brown rash that classically shows up on the palms and soles — an unusual location that's a clinical tip-off. Other signs include moist sores on mucous membranes, fever, swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue. These too resolve without treatment, sending the infection into its hidden phase.
Latent stage
The latent stage has no symptoms at all, yet the infection persists in the body for years and is still detectable on a blood test. Clinicians split it by timing: early latent means acquired within the previous twelve months (shown by a documented seroconversion, a fourfold or greater rise in titer, or recent primary or secondary signs), while late latent or unknown duration means longer than a year or a date that can't be pinned down. The split sets how long treatment runs.
Tertiary stage
In untreated cases, the tertiary stage can emerge 10 to 30 years later, though some damage appears sooner, so this isn't a guaranteed symptom-free window. This stage can wreck the heart and blood vessels, the brain, and the nervous system, and it can be fatal. The eyes and nervous system can be invaded at any stage, not only at the end: ocular syphilis (which can threaten vision) and neurosyphilis are medical emergencies, so new vision changes or neurological symptoms in someone with syphilis need same-day care StatPearls, Neurosyphilis.
How syphilis spreads
Syphilis spreads through direct contact with a syphilis sore during vaginal, anal, or oral sex. Because chancres can sit on the genitals, anus, rectum, lips, or in the mouth, transmission can happen during any of those activities, and the sore is often painless and unseen. The infection also passes from a pregnant person to their baby, the route behind congenital syphilis.
Two extra risks are worth knowing. Having syphilis roughly doubles the chance of acquiring HIV, because the open sore is an easy entry point. And untreated syphilis in pregnancy harms the baby in 50 to 80% of cases — miscarriage, stillbirth, prematurity, newborn death, or congenital infection CDC, Congenital Syphilis. Congenital cases nearly doubled in four years, from 2,163 in 2020 to 3,882 in 2023, the highest level in decades, and nearly 4,000 in 2024. See our guidance on syphilis in pregnancy & congenital syphilis for what that means for a pregnancy.
How syphilis is tested
Testing is a simple blood draw, but a single result isn't enough. Diagnosis requires two serologic tests. One is a nontreponemal test (RPR or VDRL) and the other a treponemal test (TP-PA, FTA-ABS, EIA, or CIA). Both need to point the same way before syphilis is confirmed CDC Lab Recs, 2024.
Two algorithms are acceptable. The traditional approach screens with a nontreponemal test first and confirms with a treponemal one, while the reverse-sequence approach runs a treponemal test first and confirms with a quantitative nontreponemal test. Both are valid; labs choose based on their workflow.
Timing matters here. Very early in primary infection, antibodies may not have built up yet — they can take up to about two weeks after the chancre appears, and the chancre itself shows roughly three weeks after exposure. So an early negative after a recent risk isn't reassurance, and you should retest. Read more about the right interval on our when to test after exposure page, and you can get tested or compare testing providers when you're ready.
Who should be screened
The USPSTF gives screening its strongest recommendation (Grade A) for two groups. All pregnant people should be screened early and universally regardless of risk, and if that's missed, screened at the first opportunity, even at delivery USPSTF, Pregnancy. Among nonpregnant adolescents and adults, those at increased risk should be screened, including men who have sex with men, people with HIV or other STIs, and people with a history of incarceration or sex work USPSTF, 2022.
How syphilis is treated
Penicillin G, given by injection, is the preferred drug for every stage, and it remains the only reliable cure, with no oral substitute that dependably works CDC Tx Guidelines. The dose follows the stage. We cover regimens in full on the syphilis treatment page; below is the short version.
| Stage | Penicillin regimen |
|---|---|
| Primary, secondary, early latent | Benzathine penicillin G 2.4 million units IM, single dose |
| Late latent / unknown duration, tertiary | Benzathine penicillin G 7.2 million units total — three doses of 2.4 million units IM, one week apart |
| Neuro / ocular / otosyphilis | Aqueous crystalline penicillin G 18–24 million units/day IV for 10–14 days |
One product mix-up has caused real treatment failures. The correct early-stage product is benzathine penicillin G (Bicillin L-A). The combination Bicillin C-R (benzathine plus procaine) is not an acceptable substitute. For a true penicillin allergy in non-pregnant patients, doxycycline 100 mg twice daily is an option — for 14 days in early syphilis, but a full 28 days for late latent, since the shorter course isn't enough. Azithromycin isn't recommended because of resistance CDC, Primary & Secondary.
In pregnancy, there is no safe alternative. A pregnant person who reports penicillin allergy should be desensitized and treated with penicillin, the only treatment that protects the baby. Most reported penicillin allergy is mislabeled — over 90% of people who believe they're allergic actually aren't. See syphilis in pregnancy for how desensitization works.
What treatment feels like
The treatment itself is an injection — one shot for early syphilis, three weekly shots for late or unknown-duration disease. Within the first 24 hours, many people get a short bout of fever, chills, headache, and muscle aches: the Jarisch-Herxheimer reaction, caused by dying bacteria releasing inflammatory signals, not a penicillin allergy. It affects roughly 95% of people treated for secondary syphilis and settles within about a day StatPearls, JHR. Knowing it's coming keeps people from mistaking it for an allergic reaction and abandoning a treatment that's working.
Cure is confirmed by blood titers, not by feeling better. Clinicians repeat quantitative RPR or VDRL titers at 6 and 12 months for primary and secondary syphilis, and at 6, 12, and 24 months for latent disease. A fourfold drop — say 1:32 to 1:8 — confirms success, while a fourfold rise signals reinfection or failure.
Complications if left untreated
Left untreated, syphilis can cause permanent, sometimes lethal damage:
- Cardiovascular syphilis — damage to the aorta and heart valves that can be fatal.
- Gummas — soft, tumor-like growths of tertiary syphilis that destroy tissue in skin, bone, or organs.
- Neurosyphilis — infection of the brain and spinal cord, which can cause stroke, dementia, and paralysis, and can occur at any stage.
- Ocular syphilis — eye involvement that can lead to permanent vision loss, also possible at any stage.
- Congenital syphilis — in a baby, this means miscarriage, stillbirth, neonatal death, prematurity or low birth weight, deformed bones, anemia, and brain or nerve damage including blindness and deafness.
How to prevent syphilis
Prevention combines a few proven steps: correct and consistent condom use, mutual monogamy with a partner who has tested negative, and routine screening for those at risk. For pregnancy, prenatal screening plus penicillin prevents congenital syphilis almost entirely, which is what makes the recent surge in newborn cases so frustrating to clinicians. Nearly every one of those cases was avoidable.
A newer option is DoxyPEP: 200 mg of doxycycline taken within 72 hours after sex reduced syphilis acquisition by about 73% in trials. The CDC recommends it through shared decision-making for men who have sex with men and transgender women who've had a bacterial STI in the past year CDC DoxyPEP, 2024.
When to see a clinician
See a clinician if you notice a painless sore on the genitals, anus, or mouth, an unexplained rash on the palms or soles, or if a partner tells you they have syphilis. Test after a recent risky exposure even if you feel fine, and retest if an early test was negative. Get screened during every pregnancy. Treat any new vision change or neurological symptom in someone with syphilis as an emergency and go in the same day.