Infections are the most common cause of fevers, but as the temperature rises other causes become more common.[1] Infections commonly associated with hyperpyrexia include roseola, measles and enteroviral infections.[36] Immediate aggressive cooling to less than 38.9 °C (102.0 °F) has been found to improve survival.[34] Hyperpyrexia differs from hyperthermia in that in hyperpyrexia the body's temperature regulation mechanism sets the body temperature above the normal temperature, then generates heat to achieve this temperature, while in hyperthermia the body temperature rises above its set point due to an outside source.[35]