Winter weather is not the only cause for low body temperature.

First of a five-part series about low body temperature.

by James Hubbard, M.D., M.P.H.

Scenario one: You’re out on a morning walk, maybe hunting your breakfast. It’s cool, a little breezy, but not freezing. In fact, you work up a good sweat, take off your coat. You find a spot and sit a bit. You start getting hungry and a little nauseous. It’s that empty stomach. Before long, you get up—but forget your way back home. What’s going on?

Scenario two: You visit your great-uncle to ask some advice. He’s getting up there in age but still sharp as a tack. He doesn’t answer the door. You go inside, and you can see your breath. He’s snoring in the bed, covers thrown off, stripped down to his underwear. What’s the deal? Carbon monoxide? Stroke?

In both of these scenarios, a low body temperature should be high on your cause list.

In medicine we call this hypothermia, and you don’t have to be in a snowstorm or on a mountaintop to get it. in fact, it’s not that unusual to read of hypothermia-related deaths in the Deep South, even Florida. Even Hawaii.

Well, how cold is too cold? I’m going to tell you. But first let’s talk about how our body keeps us warm.

Our body is a heat-producing machine. The chemical reactions that take place in our organs give off heat. But our heart, lungs, and kidneys, and other organs don’t like to be too hot or too cold. As with Goldilocks they prefer the temperature just right—a cozy 98.6 degrees F (37.6 degrees C), give or take a couple of degrees. In fact if your body temperature gets much lower that, it starts acting funny, even stops working altogether. Fortunately we have a built-in central air system.

If your body temperature starts getting too high, your skin tells your blood vessels to dilate—open up bigger—so they can pump the heated blood close to your skin, where the heat is released into the air. That’s why things that dilate those blood vessels, such as alcohol or even vigorous rubbing of the skin, are counterproductive when you’re trying to warm up. Your skin may feel warmer, but it’s at the expense of your vital organs getting colder because more blood has moved externally, into those dilated blood vessels.

If your body temperature starts getting too low,  the blood vessels constrict near the skin. That leaves more heated blood to warm your innards and keep those organs at a cozy 98.6 or so.

The official definition of hypothermia is body temperature below 95 degrees F, or 35 degrees C. By the time you’re that cold you’re probably shivering pretty hard, and that actually works pretty well to warm you up. It increases your metabolism, to produce more heat. But, if you don’t get out of the cold, your body tires out and the shivering stops. By that time you’re headed for major trouble because you’ve lost one your body’s last efforts to get warm.

So, besides cold weather—and it doesn’t have to be much below 50 degrees F—what else puts you at risk for a dangerously low body temperature?

I’ll write about that in the next post.

Oh, about those two scenarios. Nausea and being disoriented are two early symptoms of hypothermia. Throwing off the covers comes later. It’s called paradoxical undressing and is not that uncommon when you body temperature is getting really, really cold. As you probably think, it’s a bad sign. I’ll address common symptoms in part three of this series.


Five-Part Hypothermia Series:

  1. (This post) Low body temperature: How cold is too cold?
  2. Risk factors for hypothermia (besides cold weather)
  3. Symptoms of hypothermia
  4. Hypothermia treatment, part one: How to treat a conscious person
  5. Hypothermia treatment, part two: How to treat an unconscious person