Syphilis is a bacterial infection that spreads primarily through sexual contact and progresses through distinct stages, each with its own symptoms. While this infection has been known for centuries and can be cured with antibiotics, cases are rising sharply in many populations, making awareness and early detection more important than ever.

How Common Is Syphilis Around the World

Syphilis remains a significant global health concern despite being both preventable and curable. According to the World Health Organization, approximately 8 million adults between the ages of 15 and 49 acquired syphilis worldwide in 2022. This represents a considerable portion of the global population actively dealing with this infection. The disease does not discriminate by geography, affecting people across all continents and communities.

In the United States specifically, the situation has become particularly alarming. More than 207,000 cases of syphilis across all stages were reported in 2022, and the numbers have been climbing steadily since the early 2000s. Between 2017 and 2021 alone, syphilis cases jumped by 74 percent, marking one of the most dramatic increases in sexually transmitted infection rates seen in recent decades. This upward trend suggests that despite medical advances and available treatments, the infection is spreading more widely than in previous years.

Certain groups face disproportionately higher rates of infection. Men who have sex with men are particularly affected, accounting for roughly 36 percent of all primary and secondary syphilis cases and nearly 47 percent of male cases in 2021. However, rates are increasing across all age groups and genders, indicating that syphilis is not confined to any single demographic. Women are also experiencing rising infection rates, which has contributed to another deeply concerning trend.

The increase in congenital syphilis, which occurs when pregnant women pass the infection to their babies, has become especially troubling. In 2021, more than 2,800 cases of congenital syphilis were reported in the United States, representing a 203 percent increase since 2017. This dramatic rise means more newborns are being exposed to an infection that can cause severe health problems or even death if not addressed promptly during pregnancy.

What Causes Syphilis and How It Spreads

Syphilis is caused by a type of bacteria called Treponema pallidum. This microscopic organism is a spirochete, meaning it has a spiral or corkscrew shape that allows it to move through tissues in the body. German scientists first identified this bacterium as the cause of syphilis in 1905, solving a medical mystery that had plagued humanity for centuries. The bacteria are extremely fragile outside the human body and cannot survive for long on surfaces or in the environment, which is why direct contact is necessary for transmission.

The primary way syphilis spreads is through sexual contact. When a person has syphilis, they develop sores called chancres or other lesions on their body. The bacteria live in these sores and can be passed to another person during vaginal, anal, or oral sex when the sores come into direct contact with the soft skin of the mouth, genitals, or other mucous membranes. Even a single exposure can be enough to transmit the infection if direct contact with an infectious sore occurs.

Pregnant women with untreated syphilis can pass the bacteria to their developing babies through the placenta during pregnancy or during childbirth when the baby comes into contact with infected tissues. This is how congenital syphilis occurs. In rare cases, syphilis can also be transmitted through blood transfusions, although routine screening of donated blood in many countries has made this route of transmission extremely uncommon. Healthcare workers can potentially contract syphilis if a cut or abrasion on their skin comes into contact with infectious lesions, though this is also rare with proper precautions.

It is important to understand what does not spread syphilis. The bacteria cannot be transmitted through casual contact such as sharing toilet seats, doorknobs, swimming pools, bathtubs, or eating utensils. Hugging, shaking hands, or sitting next to someone with syphilis poses no risk. The bacteria require direct contact with infectious sores or lesions to move from one person to another.

Who Is at Higher Risk for Getting Syphilis

Anyone who is sexually active can contract syphilis, but certain behaviors and circumstances increase the likelihood of exposure to the bacteria. Understanding these risk factors helps individuals make informed decisions about their sexual health and when to seek testing. The most fundamental risk factor is having unprotected sex, meaning vaginal, anal, or oral sex without using barrier protection like condoms. Each sexual encounter with an infected partner, especially when sores are present, creates an opportunity for the bacteria to spread.

Having multiple sexual partners increases risk simply because it raises the chances of encountering someone with an undiagnosed infection. People who have sex with new partners without knowing their sexual health history face higher risk, particularly if they do not consistently use condoms. Men who have sex with men face disproportionately higher rates of syphilis infection, though the reasons for this are complex and involve multiple social, behavioral, and biological factors. Regardless of sexual orientation, anyone engaging in sexual activity without protection is vulnerable.

People living with HIV are at increased risk for acquiring syphilis, and having syphilis can also make it easier to contract or transmit HIV. This is because the sores caused by syphilis create breaks in the skin that provide entry points for other infections. The two infections often overlap in populations, and testing for one should prompt testing for the other. Sex workers and their clients also face elevated risk due to higher numbers of sexual partners and potential barriers to accessing consistent healthcare and prevention resources.

Pregnant women who have untreated syphilis, even if they do not have visible symptoms, can pass the infection to their babies. This makes all pregnant women a priority group for syphilis screening, regardless of their perceived risk level. Previous infection with syphilis does not provide immunity, meaning someone who has been successfully treated can become infected again if exposed. In fact, reinfection rates among certain populations, particularly men who have sex with men, are notably high, making repeated testing important even after successful treatment.

Recognizing the Symptoms of Syphilis

Syphilis is sometimes called the “great imitator” because its symptoms can resemble many other diseases, making it challenging to recognize without proper testing. Many people with syphilis do not notice any symptoms at all or mistake mild symptoms for other conditions. The infection progresses through four distinct stages, and the symptoms change dramatically as the disease moves from one stage to the next. Understanding these stages helps explain why syphilis can go undetected for long periods.

Primary Stage

The first stage of syphilis typically begins between 10 days and 90 days after exposure to the bacteria, with an average of about three weeks. During this primary stage, a single sore called a chancre appears at the spot where the bacteria entered the body. Most people develop only one chancre, though some may have multiple sores. These sores usually appear on the penis, vagina, vulva, anus, rectum, lips, or inside the mouth, depending on how the infection was transmitted.

The chancre has distinctive characteristics that set it apart from other sores. It is typically firm, round, and small, usually measuring between 1 and 2 centimeters in diameter. Critically, the chancre is usually painless, which is why many people do not notice it or seek medical attention. Because there is no discomfort, someone might easily overlook a chancre in a location that is not easily visible, such as inside the vagina or rectum. The sore lasts for about three to six weeks before healing on its own, even without treatment. However, this healing does not mean the infection is gone; the bacteria simply move into the next stage.

Secondary Stage

If the infection is not treated during the primary stage, it progresses to secondary syphilis approximately one to six months after the initial infection. This stage typically begins as the chancre is healing or several weeks after it has disappeared completely. The hallmark of secondary syphilis is a distinctive rash that can appear anywhere on the body but is particularly notable when it appears on the palms of the hands or soles of the feet. This rash typically looks rough, red, or reddish-brown and usually does not itch, making it different from many other skin conditions.

Beyond the rash, secondary syphilis can cause a wide array of symptoms that affect the whole body. People may develop white or gray wart-like sores in warm, moist areas such as the mouth, genitals, or anus. Additional symptoms often include fever, swollen lymph glands throughout the body, persistent sore throat, patchy hair loss on the scalp or in the beard and eyebrows, headaches, unexplained weight loss, muscle aches, and profound fatigue. These symptoms can make people feel generally unwell, similar to having the flu or another viral illness.

Like the primary stage, the symptoms of secondary syphilis eventually go away on their own even without treatment, sometimes disappearing for weeks or months before returning. This pattern of symptoms appearing and disappearing can continue for an extended period. The fact that symptoms resolve does not indicate that the infection has cleared; instead, the bacteria remain in the body and continue to cause damage silently.

Latent Stage

When symptoms from the primary and secondary stages fade away without treatment, the infection enters the latent stage. During this period, which can last for many years or even decades, there are no visible signs or symptoms of syphilis. A person in the latent stage typically feels completely healthy and may have no idea they still carry the infection. However, the bacteria remain in the body and can still be detected through blood tests. Some people may experience occasional mild flare-ups of symptoms during this stage.

The latent stage is divided into early latent syphilis, which refers to infection within the past year, and late latent syphilis, which describes infections of longer duration. During early latent syphilis, the bacteria can still be transmitted through sexual contact, though transmission becomes less likely as time passes. In late latent syphilis, sexual transmission becomes rare, but pregnant women can still pass the infection to their babies. Throughout the latent stage, the bacteria can be silently damaging internal organs, including the heart, brain, bones, and nerves, setting the stage for serious complications years later.

Tertiary Stage

Most people with untreated syphilis do not progress to the tertiary stage, but when it occurs, it is extremely serious. Tertiary syphilis typically develops 10 to 30 years after the initial infection began. During this late stage, the damage that has been accumulating silently over many years becomes apparent. The disease can affect virtually any organ system in the body, causing problems that range from debilitating to life-threatening.

Common complications of tertiary syphilis include damage to the heart and blood vessels, which can lead to conditions like aortic aneurysm, heart valve disease, and heart failure. The bacteria can cause severe neurological problems, including brain damage, dementia, personality changes, trouble with memory and decision-making, difficulty focusing, and confusion. People may develop movement disorders, muscle weakness, or difficulty coordinating muscle movements. The infection can damage the eyes, causing vision problems or even complete blindness. Soft, tumor-like growths called gummas can form on the skin, bones, liver, or other organs. Nerve damage can cause shooting pains, pins and needles sensations, and gradual destruction of joints. In some cases, tertiary syphilis leads to death.

Complications Affecting the Nervous System, Eyes, and Ears

At any stage of syphilis, the bacteria can invade the nervous system, causing neurosyphilis, spread to the eyes, causing ocular syphilis, or affect the ears, causing otosyphilis. These complications can occur with or without other symptoms and represent medical emergencies requiring immediate treatment. Neurosyphilis symptoms include severe headaches, muscle weakness, trouble with muscle movements, changes in mental state such as confusion or personality changes, and in advanced cases, dementia. These symptoms reflect damage to the brain and nervous system.

Ocular syphilis can affect any structure of the eye and presents with symptoms such as eye pain, redness, changes in vision, or even sudden blindness. This complication can cause permanent vision loss if not treated promptly. Otosyphilis typically affects the inner ear and presents with hearing loss (which can be unilateral or bilateral and may develop suddenly), persistent ringing, buzzing, roaring, or hissing sounds in the ears (a condition called tinnitus), dizziness, or vertigo (the sensation that you or your surroundings are spinning or moving). Otosyphilis can result in permanent hearing loss.

How to Prevent Syphilis Infection

Preventing syphilis involves understanding how it spreads and taking practical steps to reduce exposure to the bacteria. Because syphilis is primarily a sexually transmitted infection, most prevention strategies focus on safer sexual practices. Using condoms correctly and consistently during vaginal, anal, and oral sex is the most effective way to reduce the risk of syphilis transmission. Condoms act as a barrier that prevents direct contact with infectious sores or lesions on the genitals, though they can only protect the areas they cover. Sores on other parts of the body not covered by condoms can still transmit the infection through contact.

Limiting the number of sexual partners reduces the likelihood of encountering someone with an undiagnosed infection. Being in a long-term, mutually monogamous relationship with a partner who has been tested and does not have syphilis provides strong protection. Before beginning a sexual relationship with a new partner, having an open conversation about sexual health history and getting tested for sexually transmitted infections together can help both people make informed decisions. Waiting to have sex until after both partners have been tested removes uncertainty about infection status.

Regular testing is a crucial prevention strategy, particularly for people who are sexually active with multiple partners or who belong to groups with higher infection rates. Getting tested allows early detection and treatment before serious complications develop and before the infection can be passed to others. Pregnant women should be tested for syphilis early in their pregnancy to protect both themselves and their babies. Some healthcare providers recommend repeat testing later in pregnancy for women at higher risk.

People diagnosed with syphilis should abstain from sexual contact until they have completed treatment and been told by their healthcare provider that they are no longer infectious. Notifying sexual partners about the diagnosis is essential so they can also be tested and treated if necessary. Many public health departments offer partner notification services that can contact partners confidentially without revealing who provided their names. After successful treatment, people should continue using condoms with new partners and get retested regularly, as previous infection does not provide immunity.

How Syphilis Affects the Body

Understanding what happens inside the body when someone contracts syphilis helps explain why the infection progresses through stages and causes such varied symptoms over time. When the Treponema pallidum bacteria enter the body through a break in the skin or mucous membranes during sexual contact, they immediately begin multiplying at the site of entry. The body’s immune system recognizes these foreign invaders and sends immune cells to the area to fight them off. This immune response causes inflammation and tissue damage, which creates the characteristic chancre of primary syphilis. The sore represents the battlefield where immune cells are attempting to contain and destroy the bacteria.

However, the bacteria are remarkably effective at evading complete destruction by the immune system. While some bacteria are killed at the site of entry, others escape into the bloodstream and lymphatic system, spreading throughout the body. This dissemination explains why secondary syphilis affects so many different body systems simultaneously. The bacteria travel to the skin, causing the distinctive rash. They reach lymph nodes, causing them to swell. They circulate to various organs, triggering systemic symptoms like fever, fatigue, and general unwellness.

During the secondary stage, the body continues its battle against the bacteria. The immune response creates inflammation wherever the bacteria have settled, leading to the wide variety of symptoms people experience. Eventually, the immune system gains enough control to suppress the most obvious symptoms, but it cannot completely eliminate the bacteria. This partial success pushes the infection into the latent stage, where bacteria remain alive but relatively inactive, hidden in various tissues throughout the body.

Over years or decades, the persistent presence of bacteria causes chronic inflammation and progressive damage to tissues. In tertiary syphilis, this long-term damage becomes apparent. The bacteria can destroy blood vessel walls, particularly in the aorta, leading to aneurysms or other cardiovascular problems. In the brain and nervous system, the bacteria and the chronic immune response damage nerve tissue, causing neurological symptoms. In bones, the infection can cause inflammation and destruction of bone tissue. Soft tissue masses called gummas form when the immune system walls off areas of infection, creating nodules that can grow large enough to damage surrounding structures.

When bacteria invade the central nervous system at any stage, they can cross the blood-brain barrier and infect the fluid surrounding the brain and spinal cord. This invasion causes inflammation of the meninges (the protective membranes around the brain), blood vessels in the brain, or brain tissue itself. The resulting damage explains the neurological symptoms of neurosyphilis. In the eyes, bacteria cause inflammation of various eye structures, leading to pain, redness, and vision changes. In the inner ear, bacterial invasion and inflammation damage the delicate structures responsible for hearing and balance, causing hearing loss, tinnitus, and vertigo.

The reason syphilis causes such varied symptoms across its stages relates to where the bacteria are located, how many there are, and how the immune system is responding at any given time. Early stages involve active bacterial multiplication and acute immune responses. Later stages reflect chronic, smoldering infection with accumulated damage over time. This complex interaction between bacteria and immune system across months, years, or decades makes syphilis one of the most variable and unpredictable infections in medicine.