There are differences between pityriasis rosea and syphilis in the nature of the disease, causes, symptoms, prognosis and treatment principles. 1. Nature of the disease: pityriasis rosea is an inflammatory skin disease, not infectious; syphilis is a sexually transmitted disease, which is more harmful to health. 2. Etiology: the cause of pityriasis rosea is not clear, may be related to viral infection, mental factors, low immunity and so on. Syphilis is a sexually transmitted disease caused by syphilis spirochete, which is transmitted through sexual contact, mother and child, blood and so on. 3. Symptoms: The lesions of pityriasis rosea appear as isolated rose-colored reddish spots, with the long axis parallel to the skin lines, clear boundaries, covered with fine scales, and mild to moderate itching. The early stages of syphilis are characterized by a hard chancre and enlarged lymph nodes. In the second stage of syphilis, a syphilitic rash appears, which is characterized by red or reddish-brown papules and macules covering the skin and mucous membranes all over the body, and usually does not itch or has mild itching. When the virus spreads to the whole body, there will be patchy hair loss, vision loss, bone damage, nerve damage and other systemic symptoms. 4. Prognosis: pityriasis rosea is self-limiting, usually 4 to 8 weeks can subside naturally; while syphilis if not treated with the development of the disease will cause more harm to the body. 5. Treatment principle: pityriasis rosea can subside on its own, the main purpose of treatment is to control symptoms and shorten the course of the disease. Syphilis can be cured only after early and adequate use of antibiotics as prescribed by the doctor. If the patient has an unknown rash, it is recommended to go to the hospital under the guidance of the doctor to determine, so as not to judge the error caused by the adverse consequences.