Dense small red dots on the arm, and not painful and itchy, commonly found in the following situations: 1, blood diseases: such as allergic purpura, thrombocytopenic purpura, will cause small red dots on the arm and not painful and itchy. Through the blood routine, to determine the platelets, white blood cells, red blood cells have no problem, if there is a problem, you need to go to the hematology department for further examination, a clear diagnosis, and give the appropriate treatment. 2, extrusion or excessive exercise: local injuries caused by the rupture of capillaries, resulting in small red spots on the arm and painless, generally no major problems; 3, allergy: manifested as a rash symptoms, but does not appear to itchy, painful symptoms, you need to look at recent Whether to take certain drugs or eat certain foods, to the dermatology department for further examination, a clear diagnosis. Remove allergens and hormone therapy to improve symptoms.