Syphilis, a sexually transmitted infection (STI) caused by the Treponema pallidum (T. pallidum) bacterium, is curable at all stages of infection. The antibiotic drug penicillin G is the treatment of choice, given in one or more injections, depending on whether you have primary, secondary, latent, or tertiary syphilis.
The treatment of syphilis remains crucial as infection rates continue to soar in the United States, reaching their highest level since the 1950s. This includes syphilis cases among newborns, the number of which has increased by more than tenfold from 2014 to 2024.
Reproduced with permission from © DermNet dermnetnz.org 2023.
Understanding Syphilis Transmission
The Treponema pallidum bacterium that causes syphilis is spiral-shaped and can pass through tiny breaks in the skin or intact (unbroken) mucous membranes of the mouth, genitals, and anus.
Syphilis is mainly transmitted (passed) through oral, vaginal, or anal sex. This generally occurs when you come into contact with a syphilis sore or rash. The odds of infection from someone with early syphilis run anywhere from 51% to 64%.
Though uncommon, it is also possible to get syphilis by kissing someone who has a syphilis sore on the lip.
Another common mode of T. pallidum transmission is from a pregnant person to the fetus during pregnancy. Congenital (present at birth) syphilis mainly occurs when T. pallidum is passed to the fetus via the placenta. It can also happen during childbirth if the baby comes into contact with a syphilis sore in the vaginal canal.
Cases of syphilis have been linked to blood transfusions and organ transplants, but these are considered rare.
How Common Is Syphilis Today?
According to the Centers for Disease Control and Prevention (CDC), there were 203,500 reported cases of syphilis in the United States in 2022—an increase of nearly 80% since 2018. The number of congenital syphilis cases also rose from 1,325 in 2018 to 3,755 in 2022—an almost threefold increase over five years.
Reproduced with permission from © DermNet dermnetnz.org 2023
What Are the Symptoms Associated With Syphilis?
The symptoms of syphilis vary by the stage of infection. If left untreated, syphilis can progress through four characteristic stages—called the primary, secondary, latent, and tertiary stages—and affect multiple organ systems, often years or decades after the original infection.
Syphilis is often called the “great imitator” because the symptoms are so diverse that they can easily be mistaken for other diseases or medical conditions.
Primary Stage
Primary syphilis happens two to 12 weeks after exposure to T. pallidum. During this stage, a smooth, hard sore called a chancre will develop on your genitals, anus, or mouth. Most cases involve just a single sore, but it is possible to have more than one.
Because chancres are generally painless, you may not even know that you have the infection. This is especially true if the sore is in the vagina or anus or under the foreskin, where it may go unnoticed.
The chancre will eventually clear on its own within a few weeks or months. However, this doesn’t mean that the infection is clear; you are still highly contagious and can transmit the infection to others.
It is important to get treatment, even if your sore goes away. Left untreated, around 1 in 4 people with primary syphilis will progress to secondary syphilis.
Secondary Stage
Secondary syphilis occurs four to 10 weeks after the syphilis sore disappears, leading to the spontaneous outbreak of a bumpy, red to reddish-brown rash. The rash can cover the entire body, including the palms of your hands and the soles of your feet. The rash is usually non-itchy.
Other symptoms of secondary syphilis may include:
- Fatigue
- Fever
- Headaches
- Joint pain
- Muscle aches
- Patchy hair loss
- Sore throat
- Swollen lymph nodes
- Unintended weight loss
- Wartlike skin patches
These symptoms may persist for 12 weeks or even longer before spontaneously disappearing. Even so, you are still contagious during the secondary stage and can readily transmit the infection to others.
The symptoms will resolve whether or not you get treatment, but getting treated is the only way to prevent the disease from progressing to the next stage.
Latent Stage
If syphilis is not treated during the primary or secondary stages, it can go into an extended period of low disease activity—called latency—that can last up to 20 years or longer. Although there may be no outward signs or symptoms, the disease can progressively damage your heart, bones, nerves, and other organs.
Latent syphilis is largely silent, but roughly 1 in 4 people will experience an occasional flare-up of symptoms, which can easily be mistaken for an allergy or drug reaction.
During the early-latent stage (defined as up to one year following the initial infection), you can still transmit the infection to others. Thereafter, your risk of transmission rapidly declines. After two years, it is rare for transmission to occur.
Tertiary Stage
Around 1 in 3 untreated people will progress to the most advanced stage of infection, called tertiary syphilis. Tertiary syphilis tends to develop 10 to 30 years after the initial infection by which time the heart, kidney, and other organs may be severely—and sometimes irreversibly—damaged.
While tertiary syphilis can affect any organ system, it most commonly manifests as:
- Cardiovascular syphilis: This is a complication that causes the swelling and weakening of the heart and blood vessels. Severe cases can lead to an aortic aneurysm (swelling of the blood vessel) and rupture.
- Gummatous syphilis: This is a complication in which soft, tumor-like lesions (called gummas) form on the skin, bones, liver, and other organs, causing major damage.
- Neurosyphilis: This is when syphilis affects the central nervous system, causing seizures, personality changes, hallucinations, dementia, paralysis, and even stroke.
Neurosyphilis, Ocular Syphilis, and Otosyphilis May Occur at Any Stage
Without treatment, syphilis may spread to the nervous system eyes, or ears at any stage of the disease:
- Neurosyphilis symptoms can include severe headache, muscle weakness, and changes in mental state.
- Ocular syphilis symptoms can include eye pain, red eyes, and changes in vision.
- Otosyphilis symptoms can include hearing loss, tinnitus (noises in the ear), and dizziness or vertigo (feeling like everything is spinning around you).
Congenital Syphilis
Congenital syphilis occurs when a pregnant person passes the infection to the fetus during pregnancy or the baby during childbirth. Up to half of all babies infected with syphilis die shortly before or after birth.
Most babies born with congenital syphilis have no initial symptoms and may only develop signs by the age of 2, such as:
- Failure to gain weight
- Fever
- Fluid discharge from the nose
- Irritability
- Irritated, cracking skin around the mouth, anus, and genitals
- Painful leg or arm joints
- Secondary syphilis rash
- Swollen abdomen (caused by an enlarged liver or spleen)
If left untreated, congenital syphilis can lead to hearing loss, blindness, bone pain, and deformity of the nose, bones, and teeth.
A Word From Verywell
Prevention is the cornerstone of managing syphilis. Regular screening, safe sexual practices, and prompt treatment of any detected infections are essential strategies to curb the spread of this disease.
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Is Syphilis Curable?
Syphilis is curable at all stages. It is far easier to treat during the early stages of infection, often with a single dose of penicillin G. During the primary, secondary, and early-latent stages, between 94.5% and 100% of treated individuals will experience complete clearance of the infection.
After that, response rates steadily decline. By late latency, a single shot of penicillin G will deliver a response (cure) rate of only 56% to 63%. Because of this, multiple doses of penicillin G are needed over several weeks to ensure a complete cure.
Early detection is key to protecting yourself and others from this widespread and increasingly complicated STI.
Due to the high rates of infection and reinfection, syphilis has begun to develop resistance to some antibiotic drugs. As a result, penicillin G is today the only antibiotic recommended by the CDC for all stages of infection.
Syphilis Treatment Options
Penicillin G is the preferred antibiotic for syphilis. Also known as penicillin G potassium or benzylpenicillin, this long-acting antibiotic is given by intramuscular (IM) injection into a large muscle.
Penicillin G is preferred over other types of penicillin because it can reach parts of the body, such as the brain and spinal cord, that other forms of penicillin cannot.
The type used in the United States is called Bicillin L-A (benzathine penicillin G). Bicillin L-A is slowly absorbed after the injection, providing antibiotic action for as long as two to four weeks.
Depending on the stage of infection, the CDC recommends penicillin G in the following dosages:
| Stage | Dosage |
|---|---|
| Primary syphilis | 2.4 million units given as a single IM dose |
| Secondary syphilis | 2.4 million units given as a single IM dose |
| Early-latent syphilis | 2.4 million units given as a single IM dose |
| Late-latent syphilis | 7.2 million units total, given in three IM doses of 2.4 million units over three weeks |
| Tertiary syphilis | 7.2 million units total, given in three IM doses of 2.4 million units over three weeks |
| Congenital syphilis | Dosage based on body weight. Aqueous crystalline penicillin G administered intravenously or procaine penicillin G IM for 10 days |
Common side effects of penicillin G include injection site pain, nausea, and diarrhea.
Alternatives to Penicillin G
Other antibiotic drugs may be used if you are allergic to penicillin, some of which are highly active against T. pallidum. These include:
Doxycycline was reported to have a response rate of between 83% and 100% in people with early syphilis, while ceftriaxone was reported to have a response rate of between 65% and 100%.
Even so, penicillin G remains the gold standard of treatment, particularly for people with tertiary syphilis. If a person with tertiary syphilis has a penicillin allergy, they should be treated in consultation with an infectious disease specialist.
Does My Sex Partner Need Treatment?
If you have been treated for syphilis (primary, secondary, or early latent), your sex partners may likely need to be treated as well. The following factors determine the decision to treat or not treat:
- Sexual contacts within the past 90 days should be treated even if their test results are negative.
- Sexual contacts made more than 90 days ago should be treated if their results are unavailable and the chances of their returning for testing are low. If their results are negative, treatment is not needed.
- Long-term sex partners of someone with late latent syphilis should be treated based on the results of syphilis testing.
Syphilis Prevention and Management
Despite ongoing public awareness campaigns, syphilis rates continue to climb in the United States. By 2023, the rate of new infections had become so high that shortages of Bicillin L-A were reported nationwide. This led to the temporary importation of an alternative form of benzathine penicillin G called Extencilline.
To help reduce the spread of syphilis and protect yourself and others from infection:
- Use condoms consistently and correctly, including for oral sex.
- Reduce your number of sex partners.
- Get tested regularly for syphilis if you are sexually active. The CDC advises that sexually active men who have sex with men and people with human immunodeficiency virus (HIV) should be screened at least once yearly.
- Ask a new or prospective sex partner to get tested.
- Get tested for syphilis during your first prenatal visit if you are pregnant.
- Advise sex partners if you get syphilis so they can get tested and treated, too.
Is Syphilis a Reportable Disease?
Syphilis is a reportable disease in every state, although reporting requirements vary. In some states, sex partners are advised by a provider, clinic, or lab; in others, public health officials are tasked with notification.
With that said, don’t assume that these systems are infallible. Consider contacting your partners yourself and explaining the situation without accusation or blame. If you feel too uncomfortable or embarrassed to do so, ask your healthcare provider to notify them for you (or with you).
Summary
Syphilis is a curable sexually transmitted infection caused by the Treponema pallidum bacteria. It is mainly transmitted through oral, vaginal, or anal sex but can also be passed from pregnant person to fetus or child during pregnancy or childbirth.
Penicillin G is the treatment of choice for all stages of syphilis. Primary, secondary, and early-latent syphilis can usually be cured with one intramuscular injection. Late-latent and tertiary syphilis can usually be resolved with three intramuscular injections given over three weeks. Congenital syphilis may be treated with IV or IM penicillin for 10 days.
Sexual partners should also be tested and treated.
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