Syphilis spreads through direct contact with a syphilis sore during vaginal, anal, or oral sex. The bacterium that causes it, called Treponema pallidum, enters your body through mucous membranes or tiny breaks in the skin. You don’t need to have intercourse to get it. Any skin-to-skin contact with an active sore is enough.
How Syphilis Spreads During Sex
The sores that transmit syphilis, called chancres, typically appear on or around the penis, vagina, anus, rectum, or lips and mouth. They’re firm, round, and often painless, which means many people don’t realize they have one. When your skin or mucous membranes touch one of these sores during sexual contact, the bacteria can pass directly to you.
All three types of sexual contact carry risk. Vaginal and anal sex involve mucous membranes that the bacteria easily penetrate. Oral sex is also a transmission route, particularly when sores are present on the lips, mouth, or genitals. Because the sores can appear in places that aren’t immediately visible (inside the vagina, inside the rectum, or in the throat), a partner may not know they’re contagious.
Why Condoms Don’t Fully Protect You
Condoms reduce the risk of syphilis by blocking contact with sores, but they don’t eliminate it. The CDC classifies syphilis as a skin-to-skin infection, meaning condoms won’t reliably protect against it the way they do for infections transmitted through bodily fluids. If a sore is on an area the condom doesn’t cover (the scrotum, inner thigh, pubic area, or around the anus), transmission can still happen during otherwise protected sex.
This doesn’t mean condoms are useless. They still help when the sore happens to be in a covered area. But relying on condoms alone isn’t as effective for syphilis prevention as it is for HIV or gonorrhea.
When Someone Is Most Contagious
Syphilis is most contagious during its first two stages: primary and secondary. During the primary stage, one or more chancres appear at the site where the bacteria entered the body. These sores last three to six weeks and heal on their own, even without treatment. The infection, however, does not go away.
In the secondary stage, a rash often develops on the palms of the hands, soles of the feet, or other parts of the body. Moist, flat sores may appear in the mouth or genital area. These lesions are also highly infectious. After the secondary stage, syphilis enters a latent (hidden) phase where there are no visible symptoms. During latency, the risk of passing syphilis through sexual contact drops significantly, though the infection still lives in the body and can progress to cause serious internal damage years later.
Transmission During Pregnancy
A pregnant person with syphilis can pass the infection to their baby through the placenta during pregnancy or during delivery. This is called congenital syphilis, and it can cause stillbirth, premature birth, low birth weight, and serious health problems in the newborn. The World Health Organization notes that the risk of harm to the fetus is minimal if the mother receives treatment early in pregnancy, ideally before the second trimester. Routine prenatal screening catches most cases, but delayed or missed prenatal care remains a major factor in congenital syphilis cases.
How You Cannot Get Syphilis
Syphilis does not survive outside the human body for more than a few moments. You cannot get it from toilet seats, doorknobs, hot tubs, swimming pools, or bathtubs. Sharing clothing, towels, or eating utensils also poses no risk. Casual contact like hugging, shaking hands, or sitting next to someone with syphilis is completely safe. The bacterium requires direct contact with an active sore or the moist lesions of secondary syphilis to spread.
How Soon Symptoms Appear After Exposure
The first sore typically shows up 10 to 90 days after exposure, with an average of about 21 days. Because chancres are painless and sometimes hidden inside the body, many people never notice the primary stage at all. The sore heals on its own within a few weeks, which can create a false sense that nothing is wrong.
If untreated, secondary symptoms usually develop two to twelve weeks after the chancre appears. These can include rash, fever, swollen lymph nodes, sore throat, patchy hair loss, and fatigue. These symptoms also resolve without treatment, but again, the infection remains active.
Testing After a Possible Exposure
If you think you’ve been exposed, a blood test can detect syphilis, but timing matters. Your body needs time to produce the antibodies that tests look for. Testing too soon after exposure can return a false negative. Most guidelines recommend waiting at least two to four weeks after a suspected exposure before getting tested. If your initial test is negative but your concern remains, a follow-up test a few weeks later can provide a more definitive answer.
Syphilis is highly treatable, especially when caught early. A single course of antibiotics clears the infection in its primary and secondary stages. The longer it goes undetected, the more treatment it requires and the more potential damage it can do to the heart, brain, and nervous system.
Who Is Most at Risk
In the United States, roughly 41,500 cases of primary and secondary syphilis were reported in 2024, a rate of about 12 per 100,000 people. Men account for the majority of cases, at a rate of 17.6 per 100,000 compared to 6.9 per 100,000 for women. Men who have sex with men face disproportionately higher rates, though cases among women have risen sharply in recent years, driving a parallel increase in congenital syphilis.
Having other sexually transmitted infections, particularly HIV, increases vulnerability to syphilis. Open sores from syphilis also make it easier to acquire or transmit HIV, creating a cycle that compounds risk. Multiple sexual partners and inconsistent condom use further raise the likelihood of exposure. Regular STI screening is the most practical tool for catching syphilis before it progresses or spreads to others.