The human core temperature is maintained by highly controlled regulatory mechanisms that balance heat production and heat loss. When this balance is interrupted, there are consequences for human physiology that are not yet fully understood. Extremes of temperature have a physiological impact on human cells. In some instances, such as cardiac arrest, traumatic brain injury, and organ transplantation, controlled hypothermia can be physiologically beneficial, but hypothermia in traumatic injury is distinctly different. In trauma, hypothermia often begins at the time of injury as a result of increased heat loss by conduction and convection due to exposure and reduced heat production due to decreased motor activity.