There are several common causes of vascular swelling and pain in the arm. First, the most common reason is the sudden change from a cold environment to a hot environment, which can lead to acute dilation of blood vessels due to the change in temperature, thus causing vascular distension and discomfort. Second, vasculitis, due to irritation, or chronic sterile inflammation, and caused by the hardening of the blood vessels, resulting in vascular distension and discomfort. The third, infection, after the infusion caused by intravascular infection, which leads to vascular swelling and discomfort.