Untreated syphilis moves through a series of stages over months to decades, eventually causing permanent damage to the brain, heart, and other organs in roughly one out of three people who never receive treatment. The early stages are deceptively mild, with sores and rashes that heal on their own, which is exactly why many people assume the infection has resolved when it hasn’t. The bacteria remain in the body, silently progressing toward complications that antibiotics can no longer reverse.
Primary Stage: A Painless Sore
The first sign of syphilis is a sore at the spot where the bacteria entered your body. It typically appears on or around the genitals, anus, rectum, or mouth. The sore is usually firm, round, and painless, which means many people never notice it. It lasts 3 to 6 weeks and heals completely on its own, with or without treatment. This self-healing is misleading: the infection is still active and will progress to the next stage.
Secondary Stage: Rash and Flu-Like Symptoms
Weeks to months after the initial sore, a rash can appear on one or more areas of the body, including the palms of the hands and soles of the feet. It tends to look rough, red, or reddish-brown and often doesn’t itch. Some people barely notice it. Alongside the rash, you may develop fever, swollen lymph nodes, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and deep fatigue.
These symptoms also disappear without treatment, reinforcing the false impression that the infection is gone. But the bacteria are still multiplying and spreading through the bloodstream. Without antibiotics, the disease moves into the latent stage.
Latent Stage: Years of Silence
The latent stage has no visible signs or symptoms at all. You can carry the infection for years, even decades, without knowing it. During this phase, syphilis is not transmitted sexually, but the bacteria are still present in your body and can eventually cause serious internal damage. This is often the longest stage, and it’s the reason syphilis is sometimes called “the great imitator.” People in this phase feel healthy, which makes diagnosis unlikely unless they happen to be screened through routine blood work.
Tertiary Syphilis: Permanent Organ Damage
Between 25% and 40% of people who never receive treatment eventually develop tertiary syphilis. This can take 10 to 30 years to become clinically apparent, but when it does, the consequences are severe. Tertiary syphilis attacks in three main ways: through the cardiovascular system, the nervous system, or through destructive soft-tissue masses called gummas that can infiltrate virtually any organ.
Not everyone who goes untreated reaches this stage. But there is no way to predict who will and who won’t, and the damage it causes is largely irreversible.
How It Damages the Heart and Arteries
Cardiovascular syphilis targets the aorta, the body’s largest artery. The bacteria invade the tiny blood vessels that supply the aortic wall itself, triggering chronic inflammation. Over time, the elastic fibers and muscle cells in the artery wall break down, causing it to thin, weaken, and balloon outward. Among people with syphilitic aortitis (inflammation of the aorta), roughly 71% develop an aortic aneurysm, a bulge in the vessel wall that can rupture and become life-threatening.
When the inflammation reaches the base of the aorta near the heart, it can stretch the aortic valve ring and cause the valve to leak. This happens in about 47% of cases. The inflammation can also scar and narrow the openings of the coronary arteries where they branch off the aorta, restricting blood flow to the heart muscle in about 16.5% of cases. Unlike typical heart disease, where cholesterol plaques build up along the length of the artery, syphilitic damage creates a tight narrowing right at the artery’s origin.
How It Damages the Brain and Nervous System
Neurosyphilis can develop at any stage of the disease, but its most devastating forms appear years or decades after the initial infection. Two complications stand out.
General paresis develops 3 to 30 years after infection and affects the brain directly. It causes personality and mood changes, problems with thinking and judgment, memory and language difficulties, delusions, and seizures. Before antibiotics existed, general paresis was a common cause of psychiatric institutionalization.
Tabes dorsalis damages the spinal cord and peripheral nerves, appearing anywhere from 5 to 50 years after the original infection. It causes sudden, stabbing “lightning pains” in the arms, legs, or abdomen, along with loss of muscle coordination, walking and balance problems, bladder control issues, vision loss, and loss of reflexes. The nerve damage disrupts the body’s ability to sense its own position, making even simple movements unreliable.
Risks During Pregnancy
Untreated syphilis during pregnancy poses serious risks to the baby. A large systematic review found that among pregnant women with untreated syphilis, fetal loss and stillbirth were 21% more frequent than among uninfected women. Neonatal deaths were about 9% more frequent, and premature birth or low birth weight occurred roughly 6% more often. About 15% of surviving infants showed clinical signs of congenital syphilis at birth, which can include bone abnormalities, skin lesions, anemia, and organ damage.
This is why prenatal screening is standard practice. The CDC recommends syphilis testing at the first prenatal visit, with repeat testing at 28 weeks and at delivery for women at increased risk.
Treatment Can Cure It, but Not Undo the Damage
Syphilis at any stage can be cured with the right antibiotic. In the primary and secondary stages, treatment clears the infection before it causes lasting harm. Even in the latent and tertiary stages, antibiotics stop the disease from progressing further.
What they cannot do is repair damage that has already occurred. If syphilis has caused hearing loss, that hearing loss is permanent. If it has scarred the aortic valve or narrowed the coronary arteries, you may need surgery. If nerve damage from tabes dorsalis has taken away your ability to walk steadily, antibiotics won’t restore it. The brain changes from general paresis, including cognitive decline and personality changes, may partially stabilize with treatment but rarely fully reverse.
This gap between “curable infection” and “irreversible damage” is the core reason early detection matters so much. Every year the bacteria remain in the body increases the window for organ damage that no medication can fix.