The cardinal sign of inflammation called rubor is mainly the result of:

Inflammation can be defined as the reaction of vascularized living tissue to local injury. Celsus originally described four cardinal signs of inflammation: rubor (redness), tumor (swelling), calor (heat), and dolor (pain). Virchow later added a fifth sign, loss of function (functio laesa). Redness (rubor) and heat (calor) are primarily the result of increased blood flow, secondary to vasodilation of arterioles.