Syphilis is a bacterial infection that, left untreated, progressively damages the body over months to decades. It starts as a single painless sore, then spreads through the bloodstream to produce a body-wide rash, and can eventually destroy tissue in the brain, heart, bones, and other organs. The bacterium responsible is remarkably invasive: it penetrates mucous membranes or tiny breaks in the skin, then breaks down the connective tissue between cells to reach the bloodstream, where it spreads to virtually every organ system.
What makes syphilis deceptive is that its early symptoms disappear on their own, creating the illusion that the infection has resolved. It hasn’t. Without treatment, the bacteria remain active in the body and can cause irreversible damage years or even decades later.
The First Stage: A Painless Sore
About three weeks after exposure, a small, firm sore called a chancre appears at the spot where the bacteria entered the body. This is usually on the genitals, rectum, or mouth. The sore is typically painless, which means many people never notice it, especially if it’s inside the rectum or vagina. It heals on its own within three to six weeks, whether or not you receive treatment. That self-healing is part of what makes syphilis so easy to miss: the first visible sign simply goes away.
The Second Stage: A Body-Wide Rash
Weeks to months after the chancre heals, syphilis enters its secondary stage. The bacteria have now spread throughout the body, and the immune system responds with a constellation of symptoms. The hallmark is a rash that covers the body in a symmetrical pattern. It’s pink or dusky red, doesn’t itch, and notably appears on the palms of the hands and soles of the feet, locations that most other rashes avoid. In warm, moist areas like the groin, the rash can merge into raised, flat, grayish-white patches.
Beyond the skin, secondary syphilis causes low-grade fever, headache, fatigue, and swollen lymph nodes throughout the body. Sores can develop on the mucous membranes inside the mouth and throat. These symptoms also resolve on their own, typically within a few weeks to months, and the infection enters a quiet phase.
The Latent Phase: Silent but Present
After the secondary stage clears, syphilis goes dormant. You feel fine, you look fine, and there are no outward signs of infection. This latent period can last years or even the rest of your life without ever progressing further. But in roughly one-third of untreated cases, the infection eventually reactivates and begins attacking internal organs. During latency, blood tests can still detect the infection, which is why routine screening matters even when you feel healthy.
Tertiary Syphilis: Organ Damage
Tertiary syphilis can appear 10 to 30 years after the original infection. At this point, the bacteria cause destructive lesions called gummas, which are masses of inflamed tissue that can form in the skin, bones, liver, or virtually any organ. These lesions erode and destroy the tissue around them.
The cardiovascular system is a major target. Syphilis can damage the walls of the aorta, the body’s largest artery, leading to dangerous bulging (aneurysm) that can rupture. It can also damage heart valves. These complications are life-threatening and often irreversible by the time they’re discovered.
What Syphilis Does to the Brain and Nerves
Syphilis can invade the nervous system at any stage of infection, but the most devastating neurological damage tends to occur years to decades later. The progression follows a rough timeline. Within the first year, the bacteria can inflame the membranes surrounding the brain, causing headaches, neck stiffness, confusion, and sometimes seizures. Between 5 and 12 years after infection, syphilis can damage blood vessels in the brain, and the most common result is a stroke in a younger adult, often preceded by weeks of headaches, dizziness, mood swings, and memory problems.
The late forms of neurosyphilis are the most feared. General paresis, which typically appears 15 to 20 years after infection, is essentially a slow-motion dementia. It starts with irritability, personality changes, and forgetfulness, then progresses to memory loss, confusion, psychosis, delusions, and seizures. Another late form, tabes dorsalis, attacks the spinal cord and causes stabbing pains in the legs, loss of coordination, difficulty walking, and loss of bladder control. In one study of neurosyphilis patients, the most common symptoms were personality changes and dementia (33%), problems with balance and coordination (28%), and stroke (23%).
Effects on the Eyes and Ears
Syphilis can attack the eyes at any stage of infection, not just the late stages. It most commonly causes inflammation inside the eye (uveitis), which produces blurred vision, eye pain, redness, and sensitivity to light. It can also damage the optic nerve or the blood vessels in the retina. Without treatment, ocular syphilis can lead to permanent blindness.
The ears are similarly vulnerable. Syphilis can infect the inner ear structures responsible for hearing and balance, causing sudden hearing loss, ringing in the ears, and vertigo. The hearing loss can affect one or both ears, progress rapidly, and become permanent. These complications are important to recognize because they require more aggressive treatment than standard syphilis.
Syphilis During Pregnancy
When a pregnant person has untreated syphilis, the bacteria can cross the placenta and infect the fetus. The consequences range from premature birth to stillbirth. Some babies appear healthy at birth but develop symptoms later: rashes, enlarged liver and spleen, seizures, fevers, and bulging soft spots on the skull. As these children grow, they can develop the same devastating complications seen in adult tertiary syphilis, including deafness, blindness, and neurological damage.
Congenital syphilis has been rising sharply in the United States. Nearly 4,000 cases were reported in 2024, a figure that’s almost 700% higher than a decade ago. This increase persists even as overall syphilis cases among adults have begun to decline, largely because gaps in prenatal screening allow infections to pass undetected to newborns.
How Syphilis Is Detected
Syphilis is diagnosed through blood tests, but the timing matters. Antibodies may not become detectable until about two weeks after the initial sore appears, so testing too early can produce a false negative. The standard approach uses two types of blood tests in sequence: one that detects antibodies specific to the syphilis bacterium, and a second that measures how active the infection is. If the results conflict, a third confirmatory test resolves the discrepancy. Because syphilis can be completely silent during its latent phase, screening is recommended for anyone at increased risk, even without symptoms.
How Syphilis Is Treated
Syphilis is curable with antibiotics, and penicillin remains the standard treatment after more than 70 years. For early-stage infections (primary, secondary, or latent syphilis of less than two years), a single injection is typically all that’s needed. For late-stage or unknown-duration syphilis, treatment involves one injection per week for three consecutive weeks.
The critical distinction is that treatment can kill the bacteria and stop the infection from progressing, but it cannot reverse damage that has already occurred. Brain tissue destroyed by neurosyphilis, heart valves weakened by cardiovascular syphilis, hearing lost to inner ear damage: none of these heal once the infection is cleared. This is why early detection matters so much. Syphilis caught in its first or second stage is straightforward to cure with no lasting effects. Syphilis caught after it has been silently eroding organs for a decade or more may leave permanent disability even after successful treatment.