Staying Safe: The Low Down on Hypothermia

This is the first installment of a new series, Staying Safe. This series tackles common safety issues in being active and enjoying the outdoors safely and responsibly. Have a suggestion or a topic you’d like to learn more about? Send me an e-mail at!

Well, hello there, winter! Nice to see you again. You timed your reappearance perfectly with today’s oh-so-appropriate post!

Throughout college, I lived for the weekends, when I would jump in a car with 4 other people and head to the hills. I got involved in my university’s Mountaineering Club and went on just about every climbing or backpacking trip they ran. During the week, I spent hours at my local climbing gym, Vertical Adventures, learning to accept my fear of heights and harness it to my advantage. Having spent most of my childhood outside, these experiences were the nudge that made me go into outdoor and environmental education.

Since 2004, I’ve led backpacking / caving /survival / kayaking trips, taught outdoor skills & leadership classes to undergraduates and developed environmental education programs for people of all ages. In these years of leading backcountry trips, I’ve learned a heck of a lot. Some of these lessons are more tangible than others, and I hope to share a little of both with you in this series and through my blog in general. But for now, let’s talk about something applicable to those of us who’d like to stay active throughout the coming winter months.


The body maintains a relatively steady temperature of 98.6º (give or take a couple of degrees) through a variety of processes collectively known as thermoregulation – think sweating and shivering. In its simplest terms, thermoregulation is a balancing act between heat production and heat loss.

In less than ideal conditions, however, the body is no longer able to produce more heat than it loses. It bears mentioning that these conditions need not be extreme – the range of ambient air temperatures optimal for humans to maintain a normal core temp without stress is surprisingly small: only just below 80 to just above 85º Fahrenheit. Theoretically, hypothermia can occur anytime the air temperature is cooler than the body’s, although clearly the colder it is the higher the chances that hypothermia can get really ugly.

As internal body temperature drops, certain predictable physiological changes take place as the body progresses through the 3 stages of hypothermia. Theses stages can be set into motion in one of two ways: exposure and immersion. These are just as they sound: exposure involves gradual heat loss due to being exposed to cold air. Immersion involves rapid heat loss from being immersed in water. As runners, we’re more worried about exposure hypothermia – specifically through the evaporation of sweat.

Mild Hypothermia: 95 – 96º F

 As its core temperature beings to dip, the body reacts in a number of ways. Shivering intensifies as muscles surrounding vital organs move rapidly to release energy in the form of heat. the body shunts blood to the core – blood vessels in the appendages constrict, preventing blood from flowing to areas that are more exposed to cold air. This is why hands and feet get cold more quickly; it’s the body’s way to protect the more important organs and processes in the trunk and head.

Outwardly, you’ll notice decreases in dexterity and awareness as mild confusion sets in as you begin to experience The Umblesfumbling, stumbling, mumbling, and grumbling. 

At this point, hypothermia is still very reversible, but you must get warm QUICKLY! Eat something, find a way to create and retain heat or move it inside pronto. Time is of the essence because…

Moderate Hypothermia: 93 – 95º F

… if exposure continues, the body will only have to fight harder to maintain homeostatis. At this point, shivering becomes violent and the mind slips into a state of further confusion and disorientation. Drowsiness is common at this stage, as is a sensation of warming, as if your body temperature is rising when you’re actually progressing further into hypothermia – more on this below.

This stage of hypothermia flirts with a point of no return – if the body continues into severe hypothermia, we’re talking real danger. While rewarming at this stage is still possible, it is much more difficult and will almost certainly require medical monitoring if not intervention.

Severe Hypothermia: 90-92º F, <90º F

Once the body reaches this stage, all bets are off – this is a life-threatening situation. Many people take on a pale gray appearance with blue lips, fingers and toes. Loss of consciousness is common, and victims curl up into a fetal position. At this point, many will have lost a radial pulse entirely (found at the wrist) as blood is no longer pumping to the limbs at all.

A common phenomenon in moderate to severe hypothermia is paradoxical undressing – becoming so disoriented that one sheds layers even as he or she freezes to death. Again, the body will shunt blood from the extremities to the core. This process requires an energy output and as any active person knows, this is a finite process. Remember back to Mild Hypothermia, where I said to eat something? This is why – both shivering and vasoconstriction require energy! Eventually, though, there is no more to be spent and the muscles that are responsible for constricting vessels in the arms and legs tire, causing the vessels to relax. This relaxation allows a rush of warm blood from the core to flood into the now open vessels and leads to the feeling of overheating. This can be a vicious cycle; as clothing layers are lost, the body loses heat even more rapidly. Once this cycle begins, the case is grim.

Major functions begin to shutdown, and as core temperature drops below 90º F, the body will sometimes go into a metabolic icebox in an attempt to preserve brain function as much as possible. Hypothermia victims at this stage often appear dead – their respiration rate and heart rates can be so low that they are virtually undetectable. Although still alive at this point, the survival rate at this point is very low.

For road runners, the chances of going beyond mild hypothermia are relatively slim when compared to winter backcountry hikers, skiiers, or mountaineers. However, accidents happen and most modern day survival situations begin as a simple day hike or routine run. Being educated about and prepared for these possibilities is the first step in staying safe.

Next Up:

Conquering the Cold! Now that you know a little more about the basics of hypothermia, I’ll share some tips to keep you active, warm and safe throughout the winter!

Disclaimer: This is intended to be an introduction to hypothermia, not the definitive text. Clearly. I am NOT an M.D. or wilderness medical expert, but I’ve been a Wilderness First Responder since 2007.

Sources include: 98.6º: The Art of Keeping Your Ass Alive by Cody Lundin; Wilderness & Rescue Medicine by Jeff Isaac, PA-C, and David Johnson, M.D.; The Field Guide of Wilderness Rescue & Medicine by Jim Morrissey, EMPT-P, WEMT with David Johnson, MD; my brain; and previously used lesson plans / educational materials.


2 thoughts on “Staying Safe: The Low Down on Hypothermia

  1. Pingback: Staying Safe: Conquer the Cold This Winter «

  2. Pingback: Staying Safe: Recognizing Heat Illness «

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