Incubation period
10 to 90 days, most often around 3 weeks.
When a test becomes reliable
A blood test is reliable about 6 weeks after exposure, and certain by 12.
Symptoms
- First stage: a single firm sore, usually painless, that heals on its own in a few weeks whether or not anything is done about it
- Second stage: a rash that often reaches the palms and the soles — unusual for a rash, and a real clue — with fever, sore throat, swollen glands and patchy hair loss
- Then a latent stage with no symptoms at all, which can last years
- Late stage: damage to the heart, the brain and the nerves
Good to know
- The first sore healing on its own is the trap: people conclude it is over, and it is not
- It is called the great imitator because its second-stage rash has been mistaken for measles, allergy and psoriasis
- It can pass from a pregnant person to the baby, which is why testing in pregnancy is routine almost everywhere
- Cases have been rising across Europe since the mid-2010s
How it was discovered
A brutal epidemic swept Europe from 1495, starting among the troops besieging Naples, and every country named it after a neighbour: the French disease in Italy, the Neapolitan disease in France, the Polish disease in Russia. The name we use comes from a 1530 poem by the Veronese physician Girolamo Fracastoro about a shepherd called Syphilus who insulted the sun god and was struck with the illness. The bacterium was finally seen in 1905 by Fritz Schaudinn and Erich Hoffmann.
Last updated: September 2026
This page is general information, not a diagnosis and not medical advice. Symptoms overlap between infections, and many infections have none at all — only a test can tell. If you think you have been exposed, talk to a doctor.