Why when attempting to lower a person's body temperature in response to hyperthermia one should avoid treatments that induce shivering or vasoconstriction?

When a person shivers, the movement of the body produces heat, and the body wants to release the heat to the surface of the skin so that the body can cool. Vasoconstriction will limit the body from being able to release the load of heat to the surface of the skin, making it difficult for the person's body to cool off after heating up.