Syphilis spreads mainly through direct skin-to-skin contact with an active syphilis sore or rash during vaginal, anal, or oral sex, and from a pregnant person to their baby. The bacterium can't survive on surfaces, so toilet seats, towels, and casual contact don't transmit it CDC.
| Item | Reported cases (babies) |
|---|---|
| 2020 | 2,163 |
| 2021 | 2,881 |
| 2022 | 3,769 |
| 2023 | 3,882 |
How syphilis is actually transmitted
Syphilis is caused by the bacterium Treponema pallidum, a delicate, corkscrew-shaped organism that lives in moist body tissues and dies quickly once it's outside the body. Transmission happens when these bacteria pass from one person's sore or rash directly into another person's mucous membranes (the soft, moist lining of the genitals, anus, mouth, or throat) or through tiny breaks in the skin. That's the whole mechanism — contact with an infectious lesion, not exposure to dried fluid on an object.
Vaginal, anal, and oral sex
The most common route is sex. During the primary stage, syphilis produces a chancre — a firm, round, usually painless ulcer at the site where the bacteria entered. Touching that sore with your genitals, anus, or mouth during sex lets the bacteria cross into your tissues. Anal sex carries particular risk because the rectal lining is thin and tears easily, and a chancre tucked inside the anus or rectum often goes completely unnoticed.
Contact with a secondary-stage rash
In the secondary stage, the bacteria spread through the bloodstream and produce a rash that can cover the palms, soles, trunk, or moist areas like the mouth and genitals. The flat, wart-like patches that form in warm, damp spots (called condyloma lata) teem with bacteria and are highly contagious. Skin-to-skin contact with these lesions can transmit infection even without penetrative sex.
Kissing and oral contact
Kissing can spread syphilis only if an infectious sore or mucous patch is present on the lips or inside the mouth and your skin or mucous membrane touches it directly. Saliva alone does not carry the infection. So a kiss with a partner who has an oral chancre or a secondary mouth lesion is a real risk; an ordinary kiss with someone who has no active lesion is not.
From pregnant parent to baby
Treponema pallidum crosses the placenta and infects the fetus, and the baby can also be exposed to lesions during delivery. This is congenital syphilis, and it's serious — more on it below.
One reason syphilis spreads so quietly is that the first sore is painless and frequently hidden — inside the vagina, anus, or mouth — and it heals on its own after a few weeks. People read that healing as recovery, but the bacteria have simply moved deeper into the body while staying contagious for the duration of the early stages.
How syphilis is NOT spread
Because the bacterium dies almost immediately outside a warm, moist body, the everyday situations people worry about don't transmit it. You cannot catch syphilis from:
- Toilet seats, including in public restrooms.
- Shared towels, bedding, or clothing.
- Doorknobs, faucets, or other surfaces someone touched.
- Swimming pools, hot tubs, or baths.
- Sharing food, drinks, cups, or utensils.
- Saliva by itself, in the absence of an active oral sore.
- Casual contact — hugging, shaking hands, or sitting next to someone.
If you're trying to tell a syphilis chancre apart from a herpes outbreak — both can show up as genital sores — the lesions actually look and feel different, and the comparison is worth reading: see syphilis vs herpes.
Who's at higher risk
Syphilis is climbing across the country — roughly 53,000 primary-and-secondary cases were reported in 2023, and the late or unknown-duration stage roughly doubled from 14 to nearly 30 per 100,000 between 2020 and 2023 CDC AtlasPlus, 2023. The burden isn't evenly distributed, though. The U.S. Preventive Services Task Force gives a Grade A recommendation to screen people at increased risk USPSTF, 2022, which includes:
- Men who have sex with men (MSM), who carry a disproportionate share of cases.
- People living with HIV, partly because syphilis and HIV travel together — having syphilis roughly doubles the risk of catching HIV.
- Anyone with another diagnosed STI or a recent STI in the past year.
- People with a history of incarceration or transactional sex.
- Anyone living in or partnering within a high-prevalence community — rates vary enormously by place, from South Dakota's 73 per 100,000 down to a small fraction of that elsewhere.
Mother-to-baby transmission and newborn outcomes
Congenital syphilis is rising sharply — nearly 3,882 cases in 2023, a 77% jump from 2,163 in 2020 and the highest level in decades, with case counts climbing further since CDC. Untreated syphilis in pregnancy harms the baby in 50 to 80% of cases.
The damage can include miscarriage, stillbirth, or death shortly after birth; prematurity and low birth weight; deformed bones; anemia (a shortage of healthy red blood cells); and damage to the brain and nerves that causes blindness or deafness. What makes this so painful is that it's almost entirely preventable. The USPSTF gives early, universal prenatal screening a Grade A rating for every pregnant person, and recommends screening at the first opportunity — even at delivery — for anyone not tested earlier USPSTF. Screening plus penicillin treats the parent and protects the baby.
A note for pregnant patients who think they're allergic to penicillin: most aren't — over 90% of people who carry a penicillin-allergy label turn out not to be allergic on testing. Because penicillin is the only treatment that reliably protects the baby, a pregnant woman with a true allergy is desensitized to the drug rather than switched to a weaker alternative.
How to reduce your risk
Several layered strategies work, and combining them works best:
- Use condoms correctly and consistently. They cut transmission substantially, but only when they cover the sore — a chancre on the scrotum, groin, or mouth can still make contact.
- Choose mutual monogamy with a partner who has tested negative.
- Screen routinely if you're in an at-risk group, since many infections are silent.
- Consider DoxyPEP if you qualify. Taking 200 mg of doxycycline within 72 hours after sex reduced syphilis acquisition by about 73% in CDC's 2024 guidance, and it's recommended through shared decision-making for MSM and transgender women who've had a bacterial STI in the past year CDC DoxyPEP, 2024.
If you think you've been exposed
Don't wait for symptoms — early syphilis is often invisible. A blood test is how you find out, but timing matters because it takes a while to turn positive; check when to test after exposure and then get tested. You can read how the testing works in our guide to the syphilis test.
When to see a clinician
See a clinician promptly if you notice a painless sore on the genitals, anus, or mouth; a rash on your palms or soles; or if a partner tells you they have syphilis. Get tested in pregnancy as early as possible. And treat any new vision change or neurological symptom in someone with syphilis as an emergency — the bacteria can invade the eyes or nervous system at any stage, not just late on CDC. Syphilis is curable with the right antibiotics, and the earlier it's caught, the simpler the cure.