What is syphilis? Symptoms, causes and treatment

While sexual intercourse can provide many health benefits and increase intimacy with a partner, it can come with some risks. Having condomless sex can increase the risk of contracting a sexually transmitted infection (STI) like chlamydia, gonorrhea, syphilis or trichomoniasis.

Syphilis is an STI that is primarily spread through direct sexual contact. It’s one of the most common STIs, but it is curable with the right antibiotic. Read on to learn more about the symptoms, causes, diagnosis and treatment of this STI.

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What is syphilis?

Syphilis is a preventable and curable sexually transmitted infection caused by bacteria. It is typically spread through sexual contact and pregnancy. Many people with syphilis are asymptomatic or have mild symptoms they don’t notice. In 2022, there were 203,500 reported cases of syphilis in the United States.

History of syphilis

The first recorded cases of syphilis date back to the European outbreak in 1495. The STI spread among French soldiers led by Charles VII of France as they invaded Naples during the Italian Wars. Ultimately, this led to devastation across Europe, with syphilis (known then as grande verole or the great pox) causing people to develop abscesses, genital sores and ulcers all over their bodies.

While early syphilis didn’t directly cause a significant death toll, the use of painful and ineffective treatments like mercury inunction (rubbing ointment into the skin) and suffumigation (using fumes or smoke) led many to die from mercury poisoning.  Penicillin was later developed during World War II and became the standard treatment for this infection by 1943.

Symptoms and stages of syphilis

Syphilis can progress through four stages if left untreated: primary, secondary, latent and tertiary. Each stage has different signs and symptoms that can worsen over time without treatment.

Primary stage

“In the early stages, syphilis can start as a painless lesion. It can be subtle enough that people don't even know they're infected,” says Brennan Kruszewski, MD, board-certified internal medicine physician. These sores can appear in, on or around the anus, lips, penis, rectum or vagina or in the mouth. Sores typically last three to six weeks and should heal on their own during primary syphilis. People should seek medical care even after the sores go away to stop the infection from progressing to the secondary stage.

Secondary stage

During the second stage of syphilis, a rash may develop in places like the palms of the hands and the bottom of the feet. People may notice skin rashes when the first sore is healing or several weeks after the sore has healed.

People may also experience flu-like symptoms like fatigue, fever, sore throat and swollen lymph glands. These symptoms will disappear with or without treatment. However, if left untreated, the infection may then move into the latent and tertiary stages.

Latent stage

In the latent stage (also known as the hidden stage), there aren’t any noticeable signs or symptoms of syphilis, but the infection is still active in the body. The infection may lay dormant for years without treatment. This stage may also occur between the primary and secondary stages.

Tertiary stage

It is uncommon for people with untreated syphilis to develop tertiary syphilis. But if the infection reaches this stage, it can cause organ and tissue damage. Tertiary syphilis can affect various organ systems, such as the cardiovascular and central nervous systems. Tertiary syphilis is a serious medical condition that can develop within 10 to 30 years after initial infection. Once the STI spreads to vital organs, it can be fatal.

Congenital syphilis

Congenital syphilis is a serious medical condition that can occur if a pregnant person has untreated syphilis. The infection can pass through the placenta to the growing fetus during pregnancy or birth. Up to half of newborns that develop congenital syphilis in the womb die before or after birth.

Newborns who develop congenital syphilis before birth may not show symptoms at first. But over time, symptoms can appear. Symptoms of congenital syphilis vary by age but can include fever, inability to gain weight, irritability and skin rashes. According to Brennan Kruszewski, MD, severe complications of congenital syphilis can include blindness, facial deformities hearing loss and nervous system problems.

Syphilis causes and transmission

Syphilis is caused by the bacteria Treponema pallidum and is transmitted through direct contact with sores. Pregnant people can also pass syphilis to fetuses.

Modes of transmission

Syphilis is spread through direct contact with an infected sore during anal, oral or vaginal sex. “Sores can occur on or around the vagina, anus, or penis and may not be obvious, which contributes to the risk of infection,” Dr. Kruszewski says. “They can also be found in the rectum, on the lips or in the mouth, and can be spread from a mother to an unborn baby.”

Risk factors

Several populations are at a higher risk of developing syphilis:

• Men who have sex with men
• People who have HIV
• People who have tested positive for another STI
• People who have unprotected sex

Complications of syphilis

Untreated syphilis may lead to serious and potentially life-threatening complications. If the infection reaches the tertiary stage, it can spread to vital organs and organ systems, including the blood vessels, bones, brain, eyes, heart, joints, liver and nerves.

Ear problems

Otosyphilis, which affects the ears, is one of the rarest complications of syphilis. If syphilis is left untreated or there’s a delayed diagnosis, otosyphilis may lead to irreversible hearing loss.

Eye problems

Ocular syphilis, or eye syphilis, is a form of syphilis that can develop at any stage after infection and may affect multiple structures within the eye. “Syphilis can affect any part of the eye, and if left untreated, can result in vision loss or blindness,” Dr. Kruszewski says.

Neurological problems

Neurosyphilis is a type of syphilis that affects the central nervous system. Unlike other types of syphilis, neurosyphilis can develop at any time after infection. “If left untreated, neurosyphilis can cause problems with mood or memory, like dementia, depression, or other psychiatric issues,” Dr. Kruszewski says. “It can also result in severe or life-threatening illness, like meningitis.”

Diagnosing syphilis

If someone suspects they have syphilis, a health care provider typically administers a blood test to diagnose this STI. In some cases, Dr. Kruszewski says a health care provider will test the fluid from a sore to confirm diagnosis. Getting a diagnosis allows for early treatment that can prevent further complications.

Medical history and physical examination

“A health care provider will conduct a full history and physical exam to confirm the diagnosis of syphilis,” Dr. Kruszewski says. This may include questions about previous sexual partners, previous STIs and an examination to look for signs of syphilis, including an exam of the genital region.

During a physical exam, a health care provider looks for mouth sores (chancres), mucus patches or skin rashes on the body to confirm syphilis.

Diagnostic tests

Syphilis is diagnosed through blood tests and sores tests.

“Most cases of syphilis are diagnosed by blood tests,” Dr. Kruszewski says. “There are two main screening tests for syphilis, the rapid plasma reagin (RPR) and the Venereal Disease Research Laboratory (VDRL) test. If these tests are abnormal, an additional test is used to confirm the diagnosis.”

A health care provider may also gather a small tissue sample from a sore or rash to examine under a microscope. This can help determine if syphilis bacteria is present.

Treatment of syphilis

While syphilis is a fairly common STI, it is curable if treated with the correct antibiotics like penicillin. “The duration of therapy can vary depending on the stage of syphilis,” Dr. Kruszewski says. “Your health care provider will determine how long you need to be treated and when or if you need to be retested once your treatment is complete.”

According to Dr. Kruszewski, it is crucial to avoid sex until cleared by your health care provider, even if your symptoms have improved. Tell your sex partners that you have been diagnosed with syphilis so that they may be tested.

When to see a health care provider

“Any new sores or rashes on or near the genitals, anus, or mouth should prompt you to seek care with a health care provider,” Dr. Kruszewski says. A health care provider can perform diagnostic tests to determine if someone has syphilis. Don’t delay medical treatment, as untreated syphilis can increase the risk of serious health complications.

Prevention of syphilis

In many cases, syphilis is preventable with regular screenings and treatment. “Since syphilis may not show symptoms, it's important to be screened regularly for STIs if you are having intercourse outside of a monogamous relationship where the status of both partners is known,” Dr. Kruszeski says.

Speak with your health care provider to discuss how you can lower your risk of syphilis and other STIs.

Key takeaways

Syphilis is a common bacterial STI that’s primarily transmitted through sexual contact. The infection is treatable with antibiotics. However, if syphilis is left untreated, it can lead to serious health complications that may cause permanent organ damage and possibly death.

To help prevent syphilis, safer sex practices, such as open communication with sex partners and regular use of a barrier method like condoms, are recommended. People should also get regular STI and sexually transmitted disease (STD) testing and talk to their health care provider about STI prevention.

Frequently asked questions

What does syphilis do to a person?

Syphilis can cause painless sores to develop on the genitals, mouth or rectum. During secondary syphilis, skin rashes may appear on the palms of the hand, the bottom of the feet or other parts of the body. Later stages of syphilis may cause organ damage.

Can syphilis be cured?

Antibiotics like penicillin can cure syphilis, but they cannot reverse any damage that the infection may have caused. That’s why it’s important to diagnose it early and begin treatment.

How is syphilis transmitted?

Syphilis is typically transmitted through direct contact with sores during anal, oral or vaginal sex. Pregnant people can pass the infection to their unborn fetus through the placenta or during childbirth.

This content is for informational purposes only and is not medical advice. Consult your health care provider before taking any vitamins or supplements and prior to beginning or changing any health care practices.