Small red dots on the arms, itchy consider the following cases: 1, eczema, the disease is caused by allergic factors, may be due to wear cashmere, chemical fiber clothing caused by allergies, may also be due to contact with fertilizers, pesticides and other chemical products caused by allergies. The red spots are symmetrically distributed, the boundaries are not clear, and in addition to the red spots appear papules, papules and other polymorphic rash, if the rash fusion into a large area, and intense itching, difficult to sleep situation, this is more serious, need to static point compound glycyrrhizic acid monoammonium S sodium chloride injection, oral Epinastine hydrochloride capsule, external use of Mometasone furoate ointment coating, should also be closely observed changes in the condition. If the itching continues to worsen, you need to intramuscular injection of chlorpheniramine maleate injection; 2, purpura, caused by the rupture of small blood vessels in the skin passages, extravasation of red blood cells, should do platelet, coagulation function and other tests to clarify the cause.