Skip to main content


Medically reviewed by Last updated on Jan 22, 2024.

What is Syphilis?

Harvard Health Publishing

Syphilis is a sexually transmitted disease (STD) caused by a type of bacteria called Treponema pallidum. In its earliest stage, syphilis produces an open sore (ulcer) that leaks fluid filled with syphilis bacteria. Syphilis can be transmitted by contact with this ulcer or other infectious sores that form later in the disease, usually during vaginal, oral or anal sex. If untreated, syphilis moves through a series of stages that affect different parts of the body, although the stages can overlap:

Pregnant women with syphilis can pass the bacteria to their babies, causing a condition known as congenital syphilis. Congenital syphilis causes a variety of skin and organ problems in infants, and it can be deadly. Pregnant women with syphilis also have about a 40% chance of having a baby that is stillborn.

If you are infected with syphilis, it may be easier for you to become infected with HIV. If you already have HIV, a syphilis infection may make you more likely to spread HIV to others.


The symptoms of syphilis vary depending on the stage of the illness:

Primary syphilis — Usually, a single ulcer (chancre) appears at the site where the bacteria entered the body. The genitals are the most common location for chancres to develop, but these ulcers also can form around the mouth or anus. The chancre is firm and painless, and it oozes fluid that contains syphilis bacteria. Sometimes, lymph nodes near the ulcer become enlarged, but remain painless. The chancre of primary syphilis usually heals after one to five weeks, although the person remains infected.

Secondary syphilis — Typical symptoms of secondary syphilis are:

Without treatment, rash symptoms usually go away after two to six weeks.

Other symptoms can include:

Without treatment, these other symptoms generally last about one year.

Latent stage — This stage does not cause any symptoms.

Tertiary syphilis — In this stage, syphilis causes symptoms related to severe organ damage. These symptoms can include:


If your doctor suspects that you have syphilis, he or she will look for any of the typical symptoms of the disease, especially for a chancre in the genital area. Your doctor can diagnose syphilis by taking a sample of fluid from a suspicious ulcer and having that fluid examined under a microscope for the presence of syphilis bacteria.

Your doctor also may order blood tests to check for certain antibodies that are present in people with syphilis. However, in some cases, people without syphilis test positive for these antibodies. A positive test may have to be confirmed with a second blood test.

Because of the high risk of HIV infection in people with syphilis, public-health officials recommend that all people infected with syphilis should be tested for HIV infection.

Expected Duration

Unless treated, syphilis is a lifelong illness.


A person who has symptoms of primary or secondary syphilis can pass a syphilis infection to his or her sex partner. During sexual intercourse, the bacteria can pass from sores to the uninfected sexual partner through tiny breaks in the skin. To prevent this from happening, a person infected with syphilis (and his or her sexual partners) should abstain from sexual activity until after the completion of treatment for the infection. Every pregnant woman should have a blood test for syphilis to prevent passing the infection to her baby.


People with primary syphilis can usually be cured with a single injection of a long-acting penicillin. People in later stages require longer treatment with penicillin. Other antibiotics, including doxycycline, azithromycin or ceftriaxone may be effective for people who are allergic to penicillin. All sex partners of people with syphilis should be treated as well. Babies born with congenital syphilis should be treated with a course of penicillin.

When To Call a Professional

Contact doctor if you develop any of the symptoms of syphilis, especially if you are pregnant. If you have a sex partner who is diagnosed with syphilis, contact your doctor immediately so that you can be treated for syphilis.


With proper antibiotic treatment, early syphilis infection can be cured without causing permanent damage. Although later stages of syphilis also respond to antibiotics, treatment will not repair any organ damage caused by the disease. Without treatment, about one-third of patients with latent syphilis develop tertiary syphilis, and these patients risk severe organ damage and death.

Additional Info

CDC National Prevention Information Network (NPIN)


American Sexual Health Association

Learn more about Syphilis

Treatment options

Care guides

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.