On a given day, you may awake in a heated room, walk the dog in the blistering cold, exercise to exhaustion, take a warm bath, and rest your head back in that heated room. And through it all, your internal temperature likely remains stable between 97 and 99 degrees Fahrenheit.
But when our internal temperatures waver just a degree or two outside of that range, there can be serious, sometimes fatal, consequences. So why is it so important to maintain this equilibrium? And how does the human body regulate temperature to ensure we stay safely in that narrow pocket?
For decades, many believed the average human temperature to be 98.6 degrees, and maybe it was, but according to a recent study of 25,000 British participants conducted by Stanford researchers, the average internal temperature has actually decreased. Regardless of the exact average, the human body achieves its core temperature equilibrium through a process known as thermoregulation.
Thermoregulation involves a number of biological mechanisms designed to sense and respond to rises and falls in internal temperature. This process is essential to human health, as maintaining optimal body temperature forms a cornerstone of homeostasis, the steady state in which our bodies operate most efficiently.
But how exactly do we do it?
When the body senses a change in temperature, the central nervous system sends signals to the hypothalamus. The hypothalamus, a region of the brain vital to a number of important bodily functions, processes the information and sends signals to organs and systems in the body to counteract the change in temperature.
For example, when the body’s core temperature begins to rise, the hypothalamus sends signals to the sweat glands in the skin to produce sweat, which helps cool the skin, and the blood flowing within it, as the sweat evaporates. Similarly, the body may initiate panting, which cools the body through the evaporation of water in the mucous membranes of the throat and mouth. Vasodilation, the widening of the blood vessels under the skin, allows more blood to reach the skin, where heat radiates from the body.
On the other hand, when core temperature begins to fall, blood vessels narrow in a process known as vasoconstriction. This curtails blood flow to the skin, conserving overall body heat. The body can also perform a variety of other functions aimed at creating heat (thermogenesis), such as shivering, and increasing metabolism via hormone releases from the thyroid gland.
While the body is incredibly resourceful, humans rely on behavioral changes to adapt to rises and falls in temperature. We often don’t think about it this way, but many of our actions—seeking shade or sun, turning the thermostat up or down, huddling together or giving oneself open space—are behaviors designed to affect quick and efficient core temperature changes.
When our bodily functions and behavioral changes are unable to maintain a healthy core temperature, the body may drop below 95 degrees, which is the threshold for hypothermia. This can lead to heart failure, brain damage, and death. When the body rises above 104 degrees, it is in a state of severe hyperthermia, which can cause fatigue, cramps, heat stroke, brain damage, and death.
Now hopefully you understand a little more about the internal mechanisms and behavioral changes that work together to keep the body at a stable internal temperature so it can perform at its best.