Doxycycline alone can cure syphilis, but the drug of choice for syphilis treatment is penicillin. Doxycycline should not be used for syphilis during pregnancy and in infants and children under 8 years of age who have congenital syphilis. Syphilis is a sexually transmitted disease (STD) that affects multiple systems and organs within the body, and the damage it can cause to an individual’s health should not be overlooked. Early syphilis patients can be cured with the standardized use of antibiotic medications. Penicillin is the first choice for syphilis, but people who are allergic to penicillin can use other antibiotics, such as cephalosporin and doxycycline. Patients with syphilis can be treated with doxycycline alone when they are allergic to penicillin. Early syphilis can be cured, but in moderate to advanced syphilis combined with organic damage, the damage is irreversible. Syphilis during pregnancy, as well as infants and children under 8 years of age with congenital syphilis, are contraindicated for doxycycline. Although doxycycline can be used for the treatment of syphilis, it cannot be ruled out that some patients may have gastrointestinal reactions, allergies and other adverse reactions after using the drug. So those who are allergic to doxycycline should be prohibited. Doxycycline must be used continuously and regularly for the treatment of syphilis, so patients with syphilis should follow the doctor’s instructions to use doxycycline reasonably, and should not stop or change the dosage of the drug on their own. If there is any discomfort, consult a doctor in time and choose the best treatment plan under the doctor’s guidance.