Untreated syphilis doesn't stay still. After the first sore heals and symptoms fade, the bacterium Treponema pallidum keeps spreading silently, and over years it can damage the heart, blood vessels, brain, eyes, and nervous system, sometimes fatally CDC. The infection is curable at every stage with penicillin, but only treatment stops the progression.
| Item | Reported cases (babies) |
|---|---|
| 2020 | 2,163 |
| 2021 | 2,881 |
| 2022 | 3,769 |
| 2023 | 3,882 |
The essentials: why syphilis is dangerous when ignored
Syphilis moves through stages, and feeling better is not the same as being cured. The primary chancre, a painless, firm, round sore at the site of infection, heals on its own in 3 to 6 weeks whether or not you're treated. The secondary rash also resolves by itself. As the CDC puts it plainly: "The symptoms from this stage will go away whether or not you receive treatment. Without the right treatment, your infection will move to the latent and possibly tertiary stages."
That painless first sore is often hidden, so many cases get missed. It disappears, the body seems to recover, and the infection moves inward. From there it enters latency, where there are no symptoms at all but the infection persists for years and stays detectable on a blood test. You can read the full breakdown of syphilis symptoms stage by stage.
Cases keep climbing. There were roughly 53,000 primary-and-secondary infections in 2023, and the late/unknown-duration stage jumped from about 14 to nearly 30 per 100,000 between 2020 and 2023 CDC AtlasPlus, 2023. Rates aren't even. South Dakota (73 per 100,000), Washington DC (40), New Mexico (37), and Mississippi (30) ran several times the national average. Untreated syphilis also roughly doubles the risk of catching HIV.
What happens if syphilis goes untreated
Tertiary syphilis: heart and vessel damage
Tertiary syphilis typically appears 10 to 30 years after infection in untreated people, though some manifestations show up sooner, so latency doesn't guarantee a symptom-free window. At this stage the bacterium can damage the heart and large blood vessels (cardiovascular syphilis) and form gummas, soft tumor-like masses that destroy tissue in organs and bone. This stage can be fatal.
Neurosyphilis and ocular syphilis: not just late complications
Syphilis can invade the eyes (ocular syphilis) or the nervous system (neurosyphilis) at any stage; these aren't reserved for the end of the disease. New vision changes or neurological symptoms in anyone with syphilis are a medical emergency, because eye and brain involvement can progress to permanent vision loss or lasting neurological damage. Don't wait to see if it passes.
Syphilis in pregnancy
Untreated syphilis in pregnancy harms the baby in 50 to 80% of cases: stillbirth, prematurity, newborn death, or congenital infection. Congenital syphilis nearly doubled in four years, from 2,163 cases in 2020 to 3,882 in 2023, a 77% rise and its highest level in decades. Prenatal screening plus penicillin prevents it. See our guide on syphilis in pregnancy for the screening schedule and treatment specifics.
Symptoms by stage
- Primary: one or more painless, firm, round sores (chancres) where the bacterium entered — penis, vagina, anus, rectum, lips, or mouth; lasts 3–6 weeks.
- Secondary: a rough red or reddish-brown rash that can appear on the palms and soles or across the body, plus mucous-membrane lesions, fever, swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue.
- Latent: no symptoms at all; the infection persists for years and remains detectable by blood test.
- Tertiary: heart, blood vessel, brain, and nerve damage 10–30 years out in untreated cases; can be fatal.
How syphilis is diagnosed
Testing is a simple blood draw, but diagnosis needs two serologic tests — a nontreponemal test (RPR or VDRL) and a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) CDC lab recs, 2024. Labs use either the traditional algorithm (nontreponemal first, then treponemal confirmation) or reverse-sequence (treponemal first, then a quantitative nontreponemal); both are acceptable.
Timing matters. Serologic tests can be nonreactive in the earliest primary infection — antibodies may take up to 2 weeks after the chancre appears, and the chancre itself shows up roughly 3 weeks after exposure. A negative test soon after a recent risk doesn't rule it out, so retest rather than trusting that early negative. Here's when to test after exposure, and you can get tested when you're ready.
Treatment: penicillin cures it at every stage
Penicillin G, given by injection, is the preferred drug for every stage of syphilis CDC Tx Guidelines. No oral drug dependably substitutes. The dose follows the stage.
| Stage | 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 2.4-million-unit IM doses at 1-week intervals |
| Neuro / ocular / otosyphilis | Aqueous crystalline penicillin G 18–24 million units/day (3–4 million units IV every 4 hours, or continuous infusion) for 10–14 days |
Early latent means acquired within the preceding 12 months — documented by seroconversion, a fourfold or greater titer rise, or recent primary/secondary signs or exposure. Anything beyond a year (or unknown) is late latent, and that distinction sets the one-shot versus three-shot schedule.
This has caused real treatment-failure errors: the correct product for early syphilis is benzathine penicillin G (Bicillin L-A). The combination product Bicillin C-R (benzathine plus procaine) is not an acceptable substitute CDC P&S Tx. For neurosyphilis, an alternative is procaine penicillin G 2.4 million units IM daily plus probenecid 500 mg orally four times daily, both for 10–14 days CDC neuro Tx.
If you're allergic to penicillin
For non-pregnant adults with primary, secondary, or early latent syphilis, doxycycline 100 mg twice daily for 14 days (or tetracycline 500 mg four times daily for 14 days) is an option. Late latent or unknown duration needs the longer 28-day doxycycline course; the 14-day course is not sufficient CDC latent Tx. Azithromycin is not recommended because of resistance. Over 90% of people who think they're penicillin-allergic actually aren't, so confirm it before ruling penicillin out.
In pregnancy there's no safe alternative. A pregnant woman with a true penicillin allergy should be desensitized and treated with penicillin, the only treatment that protects the baby.
The reaction after the first shot
Within the first 24 hours, often within a couple of hours, many people get fever, chills, headache, and muscle aches. This is the Jarisch-Herxheimer reaction: dying bacteria releasing inflammatory signals, not a penicillin allergy StatPearls. It affects roughly 95% of people treated for secondary syphilis and settles within about 24 hours, so don't mistake it for an allergic reaction.
How cure is confirmed
Blood titers confirm a cure, not how you feel. Repeat quantitative nontreponemal titers (RPR/VDRL) at 6 and 12 months for primary/secondary syphilis, and at 6, 12, and 24 months for latent disease. A fourfold or greater drop (say 1:32 to 1:8) confirms the treatment worked; a fourfold rise signals reinfection or failure. See can you get syphilis again after treatment?
Prevention
- Use condoms correctly and consistently.
- Choose mutual monogamy with a partner who has tested negative.
- Get routine screening if you're at risk; it catches latent infection before it does damage.
- Consider DoxyPEP: 200 mg doxycycline within 72 hours after sex cut syphilis acquisition by about 73% in CDC data, recommended via shared decision-making for MSM and transgender women who've had a bacterial STI in the past 12 months CDC DoxyPEP, 2024.
When to see a clinician
See a clinician if you notice a painless sore, an unexplained rash on your palms or soles, or you've had a possible exposure — even if symptoms have already faded. Treat new vision changes or neurological symptoms in anyone with syphilis as an emergency. If you're pregnant, screen early; treatment prevents nearly all congenital cases.