Syphilis is a sexually transmitted infection caused by a type of bacteria called Treponema pallidum. It spreads through direct contact with a syphilis sore during vaginal, anal, or oral sex, and it can also pass from a pregnant person to their baby. Left untreated, syphilis progresses through distinct stages and can eventually damage the heart, brain, and nervous system. The good news: it’s curable with antibiotics, especially when caught early.
How Syphilis Spreads
The bacteria enter your body through mucous membranes or tiny breaks in the skin. This happens during vaginal, anal, or oral sex when you come into direct contact with an infectious sore, called a chancre. These sores can appear on the genitals, anus, rectum, lips, or inside the mouth.
Syphilis is fundamentally a skin-to-skin infection. Because sores sometimes develop in areas a condom doesn’t cover, condoms reduce the risk but don’t eliminate it entirely. The CDC notes that latex condoms provide “limited protection” against syphilis compared to their effectiveness against infections like HIV, precisely because transmission depends on whether the sore is in a covered area.
Less common routes include blood transfusion and vertical transmission during pregnancy, where the bacteria cross the placenta. You cannot get syphilis from toilet seats, doorknobs, swimming pools, or sharing utensils.
The Four Stages of Syphilis
Primary Stage
The first sign is usually a single, firm, round sore at the spot where the bacteria entered your body. It typically appears 3 to 6 weeks after exposure. The sore is painless, which is why many people never notice it, especially if it’s inside the rectum or vagina. It heals on its own within 3 to 6 weeks whether or not you get treatment. But healing doesn’t mean the infection is gone. Without antibiotics, the bacteria are still multiplying inside your body.
Secondary Stage
Weeks to months after the initial sore heals, the infection shows up as a rash. The classic pattern is rough, reddish-brown spots on the palms of the hands and soles of the feet, a location unusual enough that it’s considered a hallmark of syphilis. The rash can also appear on other parts of the body and is sometimes so faint it goes unnoticed. Other symptoms at this stage include fever, swollen lymph nodes, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and fatigue. These symptoms will also resolve on their own, but again, the infection remains active without treatment.
Latent Stage
After the secondary symptoms disappear, syphilis enters a hidden phase with no visible symptoms at all. This latent period can last for years. During early latent syphilis (roughly the first year), you can still transmit the infection. Late latent syphilis is less contagious but far from harmless. The bacteria remain in your body, and without treatment, roughly one in three people with latent syphilis will progress to the most dangerous stage.
Tertiary Stage
Tertiary syphilis can appear 10 to 30 years after the original infection. At this point, the bacteria have had decades to cause internal damage. The consequences are severe: large masses called gummas can form in the skin, bones, or organs. The infection can damage the heart and blood vessels, potentially causing aneurysms. Neurosyphilis, where the bacteria invade the brain and spinal cord, can lead to paralysis, numbness, dementia, blindness, and deafness. Tertiary syphilis can be fatal.
Syphilis During Pregnancy
A pregnant person with untreated syphilis can pass the infection to their baby through the placenta at any point during pregnancy or during delivery. This is called congenital syphilis, and its consequences are devastating. It can cause miscarriage, stillbirth, premature birth, and low birth weight. Babies born with congenital syphilis may have deformed bones, severe anemia, an enlarged liver and spleen, jaundice, skin rashes, and brain or nerve damage including blindness and deafness. Without treatment, infected newborns can die or develop seizures and developmental delays.
Cases of congenital syphilis in the U.S. have risen nearly 700% since 2015, reaching almost 4,000 reported cases in 2024. This surge is one reason public health agencies now emphasize syphilis screening during pregnancy as a critical prenatal step.
How Syphilis Is Diagnosed
Testing typically involves two steps. The first is a screening blood test that looks for antibodies your immune system produces in response to the infection. If that comes back positive, a second, more specific test confirms whether those antibodies are actually targeting syphilis bacteria rather than something else. This two-step process exists because the initial screening test can sometimes react to other conditions, including autoimmune diseases.
In some cases, a healthcare provider may swab fluid from an active sore and examine it under a microscope to look for the bacteria directly. This is less common because it requires specialized lab equipment, but it can provide a definitive answer during the primary stage when a chancre is present.
Because syphilis can be completely symptom-free for long stretches, routine screening is the only reliable way to catch it during the latent stage. Testing is a simple blood draw, and sexually active people with new or multiple partners benefit from periodic screening.
Treatment and Cure
Syphilis is curable. The standard treatment for primary and secondary syphilis is a single injection of penicillin. One shot, and the infection is cleared. For people with a penicillin allergy who aren’t pregnant, alternative antibiotics taken orally over 14 days are an option.
Later stages require more intensive treatment, typically additional injections over a longer period. Treatment at any stage can stop the infection from progressing further, but it cannot reverse damage that has already occurred to the heart, brain, or other organs. This is why early detection matters so much.
After treatment, follow-up blood tests are important to confirm that the infection has been fully cleared. Curing syphilis once doesn’t make you immune. You can be reinfected every time you’re exposed.
Who Is Most at Risk
Anyone who is sexually active can get syphilis, but certain groups face higher rates of infection. Men who have sex with men account for a disproportionate share of primary and secondary syphilis cases in the U.S. Other risk factors include having multiple sexual partners, having sex without condoms, and having HIV (which both increases susceptibility and can complicate the course of the disease).
There is some encouraging recent data. Primary and secondary syphilis cases in the U.S. declined nearly 22% in 2024, the second consecutive year of decline. Overall reported STIs also dropped 9% from the previous year. Still, the total burden remains substantial, with more than 2.2 million STI cases reported in 2024.
Reducing Your Risk
Condoms lower the risk of syphilis when the infected area is covered, but they’re not as protective against syphilis as they are against infections transmitted through bodily fluids. Sores can appear on skin that a condom doesn’t reach. That said, consistent condom use still provides meaningful risk reduction and protects against many other STIs simultaneously.
Beyond condoms, the most effective strategies are straightforward: limiting your number of sexual partners, having open conversations with partners about STI testing, and getting screened regularly if you’re sexually active with new partners. If you’re diagnosed, notifying recent sexual partners allows them to get tested and treated before the infection progresses or spreads further.