Syphilis rash. Papular syphilid skin rash on the soles of the feet of a patient with syphilis. The eruption of papular syphilides marks the onset of the secondary stage of syphilis. The rash usually appears two to six months after the primary infection. It can occur all over the body, but particularly affects the palms and soles. Syphilis is caused by infection from Treponema pallidum bacteria, which are usually transmitted sexually. Treatment of secondary syphilis is by penicillin or other antibiotics.