The cause of long red spots on the arm without pain or itching is considered to be allergic purpura and cherry angioma, as follows: I. Allergic purpura: It is considered to be allergic purpura, which is mainly due to infection, drugs and other factors, causing allergic vasculitis in the skin and small arteries, and in the clinic, you can see petechiae and ecchymosis on the skin, not accompanied by itching. In the treatment, you can take oral compound glycyrrhizin tablets and roxithromycin capsule, at the same time, you can take oral blood to expel blood stasis capsule, in the topical medicine, you can apply the mometasone furoate cream and urea Vitamin E milk mixed with topical, you can combine with the treatment of red light. Cherry angioma: considered as cherry angioma, also called vascular nevus, mainly caused by photoaging of the skin, in the middle-aged and old people’s skin can be seen painless red spots, not accompanied by itching, generally do not need to be treated and will not affect the health of the organism. If the number is too much, you can go to the dermatology department for laser treatment. For red dots on the arm do not hurt and itchy, you need to go to the regular hospital under the guidance of dermatologists, clinical treatment.