Oral syphilis refers to sores from Treponema pallidum that show up in the mouth, throat, or lips. In the first stage it's a painless chancre at the site of contact; in the second, mucous patches on the lining of the mouth. Both are commonly mistaken for canker sores, and both heal on their own while the infection persists CDC.
| Item | Reported cases (babies) |
|---|---|
| 2020 | 2,163 |
| 2021 | 2,881 |
| 2022 | 3,769 |
| 2023 | 3,882 |
The essentials: why a mouth sore can be syphilis
Syphilis is caused by the bacterium Treponema pallidum and is curable with the right antibiotics. The infection settles wherever contact happened, and oral sex puts the lips, mouth, and throat in range. A primary sore there is painless and firm, so people rarely treat it as a warning sign.
The disease moves in stages: a primary chancre, a secondary stage with rash and mucous-membrane lesions, a silent latent stage, and in untreated cases a tertiary stage years later that can damage the heart, blood vessels, brain, and nervous system, and can be fatal. With oral syphilis the first sore heals by itself in 3–6 weeks while the bacteria keep spreading inward.
Syphilis is also climbing in the U.S.: roughly 53,000 primary-and-secondary cases were reported in 2023, and the late/unknown-duration stage jumped from 14 to nearly 30 per 100,000 between 2020 and 2023 CDC, 2023. Rates aren't evenly spread. In 2023 the highest primary-and-secondary rates were in South Dakota (73 per 100,000), Washington DC (40), New Mexico (37), and Mississippi (30).
What does oral syphilis look like?
Oral syphilis looks different depending on the stage, and that variation is why it gets missed.
Primary stage: the chancre
The primary stage produces one or more painless, firm, round sores (chancres) at the site of infection, which on the mouth means the lips, tongue, or inside the cheek. Because it doesn't hurt and may sit out of view at the back of the mouth or throat, people often don't notice it. It lasts 3–6 weeks and heals with or without treatment.
Secondary stage: mucous patches
The secondary stage brings mucous-membrane lesions, flat grayish-white patches inside the mouth, alongside a rough red or reddish-brown rash that can appear on the palms and soles or the body. Other secondary symptoms include fever, swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue. These oral patches are frequently mistaken for canker sores or oral thrush.
Symptoms going away does not mean you're cured. Per the CDC, "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." The latent stage has no symptoms at all but is still detectable by blood test, and it persists for years.
Syphilis can invade the eyes or nervous system at any stage, not only late on. New vision changes or neurological symptoms in someone with syphilis are a medical emergency.
How is oral syphilis diagnosed?
Testing is a simple blood draw, but diagnosis requires two serologic tests: a nontreponemal screen plus a treponemal confirmation CDC Lab Recs, 2024. Nontreponemal tests are the RPR and VDRL; treponemal tests include the TP-PA, FTA-ABS, EIA, and CIA. Labs run them in one of two acceptable orders: traditional (nontreponemal first, then treponemal confirm) or reverse-sequence (treponemal first, then a quantitative nontreponemal).
Timing matters. Serologic tests can be nonreactive during the earliest primary infection. Antibodies may take up to 2 weeks to appear after the chancre shows up, and the chancre itself appears about 3 weeks after exposure. A negative test soon after a risky encounter doesn't clear you; if the exposure was recent, retest rather than trusting that result. Our guide on when to test after exposure walks through the windows, and you can get tested when you're ready. For the mechanics of how the blood work is interpreted, see our explainer on the syphilis test.
How is oral syphilis treated?
Penicillin G, given by injection, is the preferred drug for every stage of syphilis, and the dose follows the stage CDC STI Tx Guidelines. No oral drug dependably substitutes. Early syphilis is one shot; late or unknown-duration disease is three weekly shots. Full regimens and follow-up are covered in can syphilis be cured? yes, here's how.
| Stage | Standard treatment |
|---|---|
| Primary, secondary, early latent | Benzathine penicillin G 2.4 million units IM, single dose CDC |
| Late latent / unknown duration, tertiary | Benzathine penicillin G 7.2 million units total — 3 doses of 2.4 million units IM at 1-week intervals CDC |
| Neuro / ocular / otosyphilis | Aqueous crystalline penicillin G 18–24 million units/day IV for 10–14 days CDC |
| Penicillin allergy (non-pregnant) | Doxycycline 100 mg twice daily — 14 days (early) or 28 days (late latent) |
On the product itself: the correct drug is benzathine penicillin G (Bicillin L-A). The combination product Bicillin C-R (benzathine plus procaine) is not an acceptable substitute and has caused treatment-failure errors. For penicillin allergy in a non-pregnant patient, doxycycline 100 mg twice daily for 14 days covers early syphilis, but late latent needs the full 28-day course; the 14-day course isn't enough. Azithromycin isn't recommended because of resistance.
Pregnancy is the one situation with no workaround. A pregnant woman with syphilis at any stage who reports penicillin allergy should be desensitized and treated with penicillin, because there's no safe alternative. Over 90% of people who think they're penicillin-allergic actually aren't, and untreated syphilis in pregnancy harms the baby in 50 to 80% of cases.
What to expect after the shot
Within the first 24 hours, many people get fever, chills, headache, and muscle aches. This is the Jarisch-Herxheimer reaction, caused by dying bacteria releasing inflammatory signals, not a penicillin allergy StatPearls. It affects roughly 95% of people treated for secondary syphilis and settles within about a day, so don't mistake it for an allergic reaction and stop care.
Cure is confirmed by blood titers, not by feeling better. Clinicians repeat quantitative RPR/VDRL at 6 and 12 months for primary/secondary syphilis (and at 6, 12, and 24 months for latent). A fourfold drop, say 1:32 falling to 1:8, confirms the treatment worked; a fourfold rise signals reinfection or failure. You can be reinfected, so partners and follow-up matter. More in can you get syphilis again after treatment?
How to prevent oral syphilis
- Use condoms (and dental dams for oral sex) correctly and consistently. They cut transmission but don't cover every sore.
- Stick to mutual monogamy with a partner who's tested negative.
- Get routine screening if you're sexually active, especially in higher-risk groups.
- Consider DoxyPEP: 200 mg doxycycline within 72 hours after sex reduced syphilis acquisition by about 73% in CDC data, recommended through shared decision-making for MSM and transgender women who've had a bacterial STI in the past 12 months CDC DoxyPEP, 2024.
- If you're pregnant, get prenatal syphilis screening. Congenital syphilis nearly doubled from 2,163 cases in 2020 to 3,882 in 2023, and it's almost entirely preventable with screening plus penicillin.
When to see a clinician
See a clinician for any painless mouth, lip, or throat sore that doesn't fit a typical canker sore, especially after oral sex with a new or untested partner. A sore that heals on its own is not reassurance. Get evaluated promptly if you develop a body rash (particularly on the palms and soles), and treat new vision changes or neurological symptoms as an emergency, since syphilis can reach the eyes and nervous system at any stage.