Red spots on the arm may be caused by pityriasis rosea, purpura, cherry angiomas and other diseases, patients should consult a doctor in time to clarify the cause of treatment. 1. pityriasis rosea: red spots on the arm may be caused by pityriasis rosea, which is covered with fine scales, and some patients are also accompanied by itching, which can be treated with topical glycerite and hydrocortisone. 2. Anaphylactic purpura: red spots on the arm may also be caused by anaphylactic purpura, patients will also have joint pain, gastrointestinal discomfort, kidney damage. Acute attacks should be bed rest, if necessary, can use glucocorticoids and other drugs for treatment. 3. Cherry angioma: red spots on the arm may also be caused by cherry angioma, which is a benign vascular proliferative disease, usually without special treatment. All the above drugs should be used under the guidance of doctors.