There are many reasons that lead to the appearance of many red dots on the patient’s arm, mainly including purpura, spider nevus, follicular keratosis, and so on. 1. Purpura: If the red dots on the patient’s arm do not fade when pressed, it suggests that the dots on the patient’s arm are bleeding spots. 2. Spider nevus: if the red dots on the patient’s arm show that the center is slightly higher than the surface of the skin, and there are many tiny capillaries around the center sticking out, like spiders, then it is spider nevus, which is commonly seen in patients with cirrhosis of the liver. 3. Keratosis pilaris: the red dots on the arm are mainly keratotic papules, sometimes accompanied by itching symptoms, is a chromosomal dominant disease. There may be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.