Syphilis is a sexually transmitted infectious disease caused by the bacterium Treponema pallidum. Syphilis has a chronic course, and if left untreated, can lead to severe organ damage and death. Syphilis also follows a periodic cycle, and primary and secondary syphilis can be distinguished.

Syphilis can occur as a result of vaginal, anal, or oral sex with an infected person. The so-called primary lesion, or chancre, appears in 2–3 weeks at the site of infection. The primary chancre is a hard, painless ulcer, usually located in the genital area. After 6–8 weeks, the chancre spontaneously heals. Infection may be accompanied by local inflammation of the lymph nodes. Secondary syphilis usually develops by the tenth week of infection, resulting in characteristic lesions on the skin, which may be macular (spot-shaped), papular and scaly, or occasionally pustular. The rash may be mild, and in 25% of patients, no dermatological changes are seen. The lesions are initially pale red or pink nonitching spots with a diameter of 5–10 mm, located on the trunk and on proximal sections of the limbs. After a few weeks, red papular lesions appear; these may occur all over the body, but usually appear on the hands and feet. They rarely undergo necrosis, which gives them the appearance of pustules. Sometimes individuals develop nonspecific symptoms, such as baldness or discoloured stains similar to vitiligo. In the tertiary phase of syphilis, gummas form; these are soft tumour-like inflamed balls. The infection then spreads to the cardiovascular and central nervous systems.

Diagnostics: Syphilis can be detected by blood tests that check for the presence of nonspecific serological factors. These include the VDRL test, a positive result in which can also signify a number of other diseases; there are also specific serological tests for syphilis. Syphilis is curable if detected quickly. Treatment is based on chronic administration of antibiotics. After recovery, the blood should be tested at intervals.