Syphilis is a bacterial infection primarily transmitted through sexual contact. The infection is characterized by several stages, each with its own set of symptoms. In its first stages, known as primary and secondary syphilis, symptoms include skin sores, rashes, and flu-like symptoms. These first stages are followed by a latent stage in which the syphilis infection is still present but does not cause any symptoms. Without treatment, the disease can progress to the tertiary stage, where the infection can damage the heart, brain, blood vessels, and other organs, and (rarely) lead to death.

In the United States, the number of reported syphilis cases has been increasing since the early 2000s. According to the Centers for Disease Control and Prevention (CDC), there were over 176,000 reported cases of syphilis in the U.S. in 2021, marking a 74% increase since 2017. While the rates of syphilis are increasing among all age groups and in both men and women, the CDC also reports that men who have sex with men are disproportionately affected, accounting for 36% of all primary and secondary syphilis cases and nearly 47% of all male primary and secondary syphilis cases in 2021.

There has also been a concerning increase in rates of congenital syphilis, when an infected pregnant person passes the disease to their child during pregnancy or childbirth. In 2021, there were over 2,800 reported cases of congenital syphilis in the U.S., an increase of 203% since 2017.

Despite the rising incidence, syphilis can be effectively managed with antibiotics. With early detection and treatment, syphilis can be cured before it causes irreversible damage to organs. If the disease progresses, antibiotics can clear the bacterial infection from the body, however damage to organs may be permanent.

“It’s important to note that not only is treatment advantageous for the infected individual, it helps the public health goal to decrease transmission to others,” says Yale Medicine infectious diseases specialist Dana Dunne, MD, MHS.

Syphilis is a bacterial infection most often transmitted via sexual contact. It is characterized by a progression through several stages:

• Primary syphilis, typically characterized by a single painless sore (called a chancre)
• Secondary syphilis, often marked by a skin rash, swollen lymph nodes, fever, and patchy hair loss, among other symptoms
• Latent syphilis, a period that may last for years or even decades in which the infection is present in the body but does not cause symptoms
• Tertiary syphilis, which occurs years or decades after the initial infection and is characterized by damage to organs and other parts of the body, including the heart, brain, and blood vessels.

At any stage of syphilis, the infection can affect the nervous system (called neurosyphilis), eyes (ocular syphilis), and/or ears (otosyphilis).

Syphilis is caused by the bacterium Treponema pallidum, which is primarily transmitted through direct contact with a syphilis sore or rash during sexual activities, including vaginal, anal, and/or oral sex.

In addition to sexual transmission, an infected mother can pass syphilis to her unborn child through the placenta during pregnancy or during childbirth through contact with a sore or rash, resulting in a condition known as congenital syphilis. It can also be transmitted through blood transfusions, though routine screening of donated blood limits this risk in the U.S.

Syphilis is not spread through contact with objects touched by an individual with the condition, such as toilet seats, doorknobs, swimming pools, bathtubs, or shared clothing or eating utensils.

Syphilis can be transmitted via sexual contact during the primary, secondary, and early latent (i.e., infection that occurred within the previous 12 months) stages. During the late latent and tertiary stages, syphilis cannot be transmitted through sexual contact, though it can still be passed from a pregnant person to their fetus. People who have been infected by Treponema pallidum can no longer transmit syphilis to others once they complete their treatment and any sores have completely healed.

Each stage of syphilis has its own symptoms:

• Primary syphilis. Symptoms of primary syphilis, which can appear three to 90 days after exposure to bacteria, include:
• A chancre at the infection site, often on the penis, vulva, or vagina, but it can appear on the cervix, anus, rectum, lips, throat, hands, perineum (the space between the anus and genitals), or other parts of the body. Less commonly, there are multiple sores. Sores are usually firm and round and typically last for three to six weeks before healing on their own.
• Secondary syphilis. The symptoms of secondary syphilis, which usually begin about two weeks to three months after the initial appearance of a sore, include:
• Skin rash that typically does not itch; it may be widespread or restricted to a localized area and can develop on the palms of the hands or the soles of the feet.
• Sores, known as mucous patches, may develop in the mouth and/or on the tongue or genitalia
• Condylomata lata (raised gray or white lesions that can develop in moist areas, such as the mouth, genitals, anus, and armpits)
• Flu-like symptoms, including fever, sore throat, fatigue, and muscle and/or joint aches
• Weight loss
• Patchy hair loss (may affect the scalp, eyebrows, or beard)
• Headaches
• Swollen lymph nodes

In about 10% of people, secondary syphilis affects other organs, such as the eyes, bones, joints, kidneys, liver, spleen, or meninges (the membranes that cover the brain and spinal cord). If left untreated, the symptoms of secondary syphilis will resolve on their own within two to six weeks, even though the infection remains.

• Latent syphilis: In latent syphilis, the bacterial infection is still present in the body but does not cause symptoms. This stage can last for years or decades. Latent syphilis is divided into two stages:
  • Early latent, in which the infection occurred within the past 12 months. Syphilis is contagious at this stage.
  • Late latent, in which the infection occurred over 12 months ago. It is thought that syphilis cannot be transmitted through sexual contact in this stage, though pregnant people can still pass the condition to their fetus.

• Tertiary (late-stage) Syphilis: This stage can occur five to 30 years or longer after the initial infection. During this stage, approximately 30% of people who aren’t treated during previous stages will develop complications that affect organs and tissues throughout the body, including the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints. Symptoms depend on the part of the body affected. The three main types of tertiary syphilis are:
  • Neurosyphilis, when the infection spreads to the brain and/or spinal cord, causing headaches, muscle weakness, personality changes, and memory problems (though neurologic involvement can also occur in earlier stages as well)
  • Cardiovascular syphilis, when the infection spreads to the aorta and other blood vessels that connect to the heart
  • Gummatous syphilis, when rubbery growths called gummas form on the skin, bones, or organs

At any stage of the disease, syphilis can affect the eyes (ocular syphilis) and ears (otosyphilis). Symptoms of these forms of syphilis can include:

• Ocular syphilis: eye pain, light sensitivity, blurred vision, and loss of vision
• Otosyphilis: tinnitus (ringing in the ears), hearing loss, dizziness, vertigo, and balance problems

Congenital syphilis can cause stillbirth, preterm birth, miscarriage, low birth weight, and newborn death. Newborns with congenital syphilis may not have symptoms. When symptoms do occur, they may include:

• Bone abnormalities
• Anemia
• Enlarged liver and spleen
• Swollen lymph nodes
• Jaundice (yellowing of the eyes and/or skin)
• Skin rash
• Poor growth
• Vision problems, including blindness
• Hearing problems, including deafness

To diagnose syphilis, your doctor will review your medical history, conduct a physical exam, and order one or more diagnostic tests.

Your doctor may begin their evaluation by asking questions related to your sexual activities, including whether you use condoms and if you've ever had a sexually transmitted infection before. They may also ask about any symptoms, such as sores or rashes. During the physical exam, the doctor will look for signs of syphilis. They may check for sores, a rash that may affect the palms or soles, or other signs.
There are several diagnostic tests that can be used to confirm a syphilis diagnosis:

• Blood tests. Two types of blood tests are required to diagnose syphilis. The order in which they are performed depends upon the laboratory:
• Nontreponemal tests do not directly detect Treponema pallidum, the bacteria that causes syphilis. Instead, they check for the presence of non-specific antibodies produced in people with syphilis. However, because these antibodies can also be produced in other disease states, syphilis will always need to be confirmed with treponemal tests (more on that below), if the laboratory is using nontreponemal tests as the initial screening test.
• Treponemal tests detect specific antibodies that the body produces in response to Treponema pallidum. This kind of test is usually used to confirm the results of a nontreponemal test. (Once an individual has syphilis, treponemal tests will remain positive for the rest of their lives, regardless of whether the disease has been treated or is active.) If your laboratory routine starts with a treponemal test, any positive result will be followed with a nontreponemal test. This is because the latter gives information about how active the disease is, and the result is used to monitor how well treatment is working.
• Direct fluorescent antibody (DFA) test. For this test, a fluorescent dye is added to the tissue sample. If Treponema pallidum is present, the dye will glow when the sample is examined under a special microscope. Skin biopsies, liver biopsies, or other tissue may be examined in this way when blood tests are inconclusive.
• Cerebrospinal fluid (CSF) test. If the doctor suspects that syphilis has affected the nervous system, they may perform a spinal tap (or lumbar puncture) to collect a sample of CSF, the fluid that surrounds the brain and spinal cord, to check for possible antibodies or other evidence that syphilis could be affecting the central nervous system (CNS).

If you've been diagnosed with syphilis, it’s important to notify your sexual partners so they can be tested and treated, if necessary. Many state health departments can help you with partner notification in a confidential and professional manner.

The bacteria can be completely cleared from the body using penicillin or, less commonly, other antibiotics such as doxycycline, tetracycline, or ceftriaxone.

• Primary, secondary, and early latent syphilis are treated with a single shot of penicillin.
• Late latent and tertiary syphilis without neurosyphilis are treated with three doses of penicillin given by injection at one-week intervals.
• Neurosyphilis, ocular syphilis, and otosyphilis are treated with a 10- to 14-day course of intravenous (IV) antibiotics. An alternative treatment involves daily injections of penicillin, as well as a medication called probenecid, taken orally four times per day for 10 to 14 days. Probenecid makes penicillin more effective by preventing it from passing out of the body in urine, thereby increasing its levels in the blood. (For those with neurosyphilis, additional doses of a different form of penicillin may be given weekly for one to three weeks.)

Pregnant people are treated with penicillin, the only antibiotic known to effectively treat the fetus and prevent congenital syphilis. The specific treatment regimen varies based on the stage of syphilis. Newborns with congenital syphilis are typically treated with penicillin administered intravenously (typically for 10 days) or, in some cases, as a single-dose injection.

After treatment, periodic blood tests—at six months and one year after treatment—are needed to confirm that the infection has cleared.

If syphilis has caused damage to organs or other tissues—or has invaded the eyes, ears, or brain, additional treatment may be necessary. In some cases, damage to organs and tissues may be permanent.

In the early stages (primary, secondary, or early latent syphilis), the disease is usually curable with appropriate antibiotic treatment. However, even after successful treatment, it's possible to get infected again, so ongoing preventive measures and regular testing are crucial.

If syphilis is not treated and progresses to tertiary syphilis, it can lead to serious health problems, including damage to the heart, brain, and other organs. Antibiotics can eliminate the bacterial infection, but damage to organs and other tissues may require additional treatment and may be permanent.

To prevent transmission, people who are diagnosed with and being treated for syphilis should abstain from sexual activity until all treatment is finished and tests show the infection is gone.