The French pox is an old name for syphilis, a sexually transmitted infection caused by a corkscrew-shaped bacterium. The term dates to the late 1400s, when a devastating outbreak swept through Europe and each country blamed its neighbors for spreading the disease. Italians, Germans, and the English called it “the French disease,” while the French called it “the Neapolitan disease.” The name stuck in English-speaking countries for centuries before the word “syphilis” gradually replaced it.
Why It Was Called the French Pox
In the 1490s, a massive outbreak of a new and terrifying disease tore through armies and cities across Europe. Every affected population pointed the finger at someone else. The Russians called it “the Polish disease.” The Polish called it “the German disease.” The Danish, Portuguese, and North Africans called it “the Spanish disease.” The Turks called it “the Christian disease.” In northern India, Muslims blamed Hindus, Hindus blamed Muslims, and eventually everyone blamed the Europeans.
The English and Italians settled on “French disease” or “French pox,” and that label dominated English-language usage for roughly 300 years. It was also called “the Great Pox,” from the French “la grosse vérole,” to distinguish it from smallpox (“la petite vérole”). The pox in both names referred to the skin lesions each disease produced, but syphilis caused far larger, more disfiguring sores.
The name “syphilis” itself comes from a poem. In 1521, the Italian physician and scholar Girolamo Fracastoro wrote a long poem called “Syphilis sive Morbus Gallicus” (Syphilis, or the French Disease), which described the origin, symptoms, and treatment of the illness through mythological storytelling. Fracastoro gave the disease to a fictional character named Syphilus, and the name gradually entered medical vocabulary, eventually replacing all the nationalist blame-names.
What Causes It
Syphilis is caused by a bacterium called Treponema pallidum, a spiral-shaped organism so thin it’s invisible under a standard microscope. It’s remarkably fragile outside the human body, unable to survive normal environmental conditions or even be grown reliably in a lab. Yet inside a person, it’s exceptionally good at hiding. The bacterium has very few proteins on its outer surface, which makes it nearly invisible to the immune system. It can also change the structure of its surface proteins over time, staying a step ahead of the body’s defenses. This is why untreated syphilis can persist for decades.
How the Disease Progresses
Syphilis moves through distinct stages, each with different symptoms and timelines. The gaps between stages, and the fact that symptoms often disappear on their own, made it deeply confusing to doctors for centuries.
Primary Stage
The first sign is usually a sore at the spot where the bacterium entered the body. These sores are typically firm, round, and painless, which means many people never notice them, especially if they appear internally. The sore lasts three to six weeks and heals on its own whether or not the person receives treatment. Healing does not mean the infection is gone.
Secondary Stage
Weeks to months later, a rash can appear on one or more areas of the body, often including the palms of the hands and soles of the feet. The rash is rough and reddish-brown, and it usually doesn’t itch. Other symptoms at this stage include fever, swollen lymph nodes, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and fatigue. Like the primary sore, these symptoms eventually disappear without treatment, which historically led many people to believe they had recovered.
Latent and Tertiary Stages
After the secondary symptoms fade, syphilis enters a latent stage with no visible signs at all. This silent period can last years. Most people with untreated syphilis never progress beyond this point, but those who do develop tertiary syphilis face severe consequences. Tertiary disease typically appears 10 to 30 years after the initial infection and can damage the heart, blood vessels, brain, and nervous system.
Neurological complications include cognitive decline, psychosis, dementia, and a condition called tabes dorsalis that damages the spinal cord and causes difficulty walking. Cardiovascular effects include inflammation of the aorta, aortic aneurysms, heart failure, and an elevated risk of stroke. A large-scale study of nearly 29,000 patients found that people with syphilis had significantly higher rates of heart attack, heart failure, and both types of stroke compared to the general population.
How It Was Treated Before Antibiotics
For centuries, treatments for the French pox ranged from ineffective to outright dangerous. One of the earliest European remedies was guaiacum, a wood imported from the Dominican Republic starting in 1508. The treatment regimen was brutal: patients were given enemas to induce diarrhea, then confined to a dark, hot room for 40 days while fasting and sweating profusely. Guaiacum was applied both as an ointment and taken as a drink. It eventually fell out of favor because it didn’t work.
Mercury was the other mainstay, applied as ointments, taken orally, or even inhaled as vapor. It produced severe side effects, including tooth loss, kidney damage, and neurological problems. The popular saying of the era captured the grim choice: “A night with Venus, a lifetime with Mercury.” These treatments persisted for roughly 400 years until the early 20th century brought more effective options, ultimately leading to penicillin, which remains the preferred treatment today.
Syphilis Today
Syphilis never disappeared. In the United States, provisional 2024 data from the CDC recorded roughly 190,000 total syphilis cases across all stages. There is some encouraging news: primary and secondary cases (the most infectious stages) dropped 22% from 2023 to 2024, falling to about 41,500 cases. That’s the second consecutive year of decline.
The picture is more troubling for congenital syphilis, which occurs when the infection passes from a pregnant person to their baby. Those cases rose for the twelfth year in a row, reaching nearly 4,000 in 2024. Congenital syphilis can cause stillbirth, severe birth defects, and lifelong health problems. Penicillin remains highly effective at every stage of the disease, and treatment during pregnancy can prevent transmission to the baby. Syphilis is one of the few sexually transmitted infections that is completely curable with a single class of antibiotic that has worked reliably since the 1940s.