There is still a certain degree of contagiousness after three shots of penicillin for syphilis, but there is no contagiousness if it is cured. Usually, after three injections of penicillin, the infectiousness of syphilis patients will be significantly reduced, but the infectiousness will not be completely disappeared, usually need to do a good job of protection, to avoid causing cross-infection. Syphilis is caused by syphilis spirochete infection, most of the infections by sexual transmission, a small portion of blood transmission and mother-to-child transmission, and the syphilis spirochete has a high degree of sensitivity to penicillin, syphilis, once diagnosed, to take a sufficient amount of penicillin treatment, such as benzylpenicillin, procainamide penicillin, etc., after three injections of treatment, the syphilis spirochete content of the patient’s body a large number of reduced. Although after three injections, the syphilis spirochetes in the patient’s body can be mostly killed, and the infectiousness is reduced a lot, but it is not completely free of infectiousness. If cured, there is no contagious. It is recommended that patients usually do a good job of daily protection, avoid sex, avoid sharing personal items with others, pay more attention to rest, increase exercise, enhance physical fitness.