Red spots on the skin of the body without pain or itching are considered to be caused by pityriasis rosea, syphilis, psoriasis and pityriasis simplex. 1. pityriasis rosea: an inflammatory skin disease of unknown etiology, which can lead to the appearance of rose-colored patches and papules covered with pityriasis scales, often occurring on the trunk and proximal extremities. 2. Syphilis: when syphilis develops to the second stage, it can lead to the appearance of a generalized rash, that is, syphilis rash, mainly manifested in the form of macular rash, maculopapular rash and papules, and there is no specificity, so it’s easy to be confused with many skin diseases. 3. Psoriasis: it is a kind of skin disease caused by the interaction of genetic factors, immune factors, environmental factors, etc. It is mainly manifested as scaly erythema or plaque, which can be confined to one place or generalized all over the body, and the lesions usually have no itching and pain. 4. Furfura simplex: belongs to a kind of skin inflammatory disease whose cause is not obvious, which can lead to the appearance of round or oval hypopigmented patches on the skin of the patient, with different sizes and clear boundaries, covered with a little fine scales. Patients usually have no conscious symptoms, and the condition may subside naturally after a few months or more. As there are many causes of painless and itchy erythema, it is recommended to go to the hospital in time to improve the examination for diagnosis and identification.