When body temperature exceeds 39-40°C, the body begins to expend excessive energy, and the cardiovascular and respiratory systems work faster. In this state, the body constricts blood vessels in the arms and legs, sending less blood to these areas, while prioritizing blood flow to vital organs such as the brain, heart, and liver. This can lead to a mottled or marbled appearance of the skin, with coldness in the extremities despite a high core body temperature. While not every rise in fever requires panic, it is important to pay special attention to fevers exceeding 40°C.