Untreated syphilis moves through four distinct stages over years to decades, progressively damaging the skin, brain, heart, and bones. Early on, it causes painless sores and rashes that heal on their own, which is precisely what makes it dangerous: the infection doesn’t go away, it just goes quiet. Without antibiotics, roughly 30% to 40% of infected people eventually develop severe, sometimes fatal complications affecting major organs.
Primary Stage: A Painless Sore That Heals on Its Own
About three weeks after exposure, a firm, painless sore called a chancre appears at the site where the bacteria entered the body. This is typically on the genitals, rectum, or mouth. The sore lasts 3 to 6 weeks and then heals completely, with or without treatment. Because it doesn’t hurt and may be hidden inside the body, many people never notice it. The bacteria, however, remain in the bloodstream and continue spreading.
Secondary Stage: Rash and Systemic Symptoms
Weeks to months later, the infection becomes systemic. The hallmark sign is a rash of round, brownish papules that appears on the trunk, back, and, distinctively, the palms of the hands and soles of the feet. Up to 90% of people in this stage develop some version of this rash, though it can be subtle enough to mistake for another skin condition. Moist, flat growths may appear in the genital area, and painless grey patches can develop on the inside of the mouth and on the palate.
Some people also experience fever, fatigue, sore throat, weight loss, and patchy hair loss. Like the primary sore, these symptoms eventually resolve on their own, even without treatment. This is the second false signal that the infection has gone away. It hasn’t.
Latent Stage: Silent but Still Present
Once secondary symptoms clear, syphilis enters its latent, or hidden, stage. There are no visible symptoms at all. Doctors divide this phase into early latent (less than one year of infection by U.S. classification) and late latent (beyond that point). During early latent syphilis, symptoms can still flare back up. During late latent syphilis, the bacteria become dormant in the body’s tissues, potentially for years or even decades.
This stage is only detectable through a blood test. You can carry the infection for years with no outward sign that anything is wrong, while the bacteria quietly position themselves in the nervous system, cardiovascular system, or other organs.
Tertiary Stage: Organ Damage
Tertiary syphilis typically develops 10 to 30 years after the original infection. It affects an estimated 30% to 40% of people who were never treated. At this point, the damage is serious, often irreversible, and falls into three main categories.
Gummatous Syphilis
Soft, tumor-like masses called gummas can form in the skin, bones, liver, and other organs. These are areas of chronic inflammation and tissue destruction. They can erode through bone and soft tissue, causing disfigurement and organ damage.
Cardiovascular Syphilis
The bacteria can invade the wall of the aorta, the body’s largest artery, triggering chronic inflammation that weakens the vessel. This most commonly affects the ascending aorta (the section closest to the heart) in about 50% of cardiovascular syphilis cases. Over time, the artery wall loses its elasticity and balloons outward, forming an aneurysm. About 10% of people with syphilitic aortic inflammation develop an aneurysm, valve damage, or narrowing of the arteries that supply the heart. In severe cases, the aortic valve stretches so badly that the heart enlarges dramatically trying to compensate. An aortic aneurysm can rupture, which is life-threatening.
Neurosyphilis
When the bacteria cross into the brain and spinal cord, the result is neurosyphilis. Early symptoms include irritability, forgetfulness, personality changes, headaches, and sleep problems. As the disease progresses, it can cause emotional instability, impaired judgment, hallucinations, delusions, seizures, and full dementia. Some patients develop a condition called tabes dorsalis, where degeneration in the spinal cord leads to an unsteady gait, sudden shooting pains in the legs, loss of sensation, bladder problems, and vision impairment. Muscle weakness, tremors, and difficulty speaking are also common in late-stage cases.
Effects During Pregnancy
Untreated syphilis during pregnancy is particularly devastating. A systematic review published in the Bulletin of the World Health Organization found that among pregnant women with untreated syphilis, fetal loss and stillbirth were 21% more frequent than in uninfected women. Neonatal deaths were 9.3% more frequent, and premature birth or low birth weight was 5.8% more frequent. About 15% of surviving infants showed clinical signs of congenital syphilis, which can include bone deformities, skin rashes, liver problems, anemia, and developmental delays.
Why the Damage Becomes Permanent
Syphilis at any stage can be cured with antibiotics. The critical distinction is between curing the infection and reversing the damage it has already caused. In the primary and secondary stages, treatment clears the bacteria before significant organ harm occurs. Once tertiary syphilis develops, antibiotics will stop the infection from progressing further, but they cannot repair damage to the heart, brain, spinal cord, bones, or eyes. Syphilis can permanently cause blindness, paralysis, dementia, and heart failure.
This is what makes the long, symptom-free latent period so dangerous. The window for full recovery without lasting consequences closes quietly, often years before a person realizes anything is wrong.
How Common Late-Stage Syphilis Still Is
Syphilis is not a relic of the past. Provisional CDC data for 2024 recorded over 190,000 total syphilis cases in the United States, and roughly 97,000 of those were classified as unknown duration or late syphilis. That late-stage category has more than doubled since 2020, with cases among women increasing by 164% over that five-year period. The rise reflects both increasing transmission and gaps in screening, meaning more people are being diagnosed only after the infection has been present for a long time.