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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

The Ups and Downs of Body Temperature

May 08, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Do you feel cold when others are comfortable? Or, do you tend to feel warm all the time?

Either way, it's probably not because your body's temperature is fluctuating wildly. In fact, your body is remarkably good at keeping your temperature within a normal range at all times.

That's important, because the health of the tissues and organs throughout your body depends on a fairly tight control of temperature. Millions of chemical reactions are taking place in our cells every minute. And they must occur at a particular temperature.

So, it's a myth that healthy people tend to have significantly different body temperatures from one another. Most of them have body temperatures that vary within a narrow range.

Your body temperature does not necessarily remain at precisely 98.6 degrees Farenheit at all times. But it fluctuates within a pretty tight range — rarely more than a degree higher or lower, unless something's wrong.

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How Your Body's Thermostat Works


Think of the body like a furnace. Normal bodily functions and activities (including exercise) generate heat. The trick is for your body to protect itself from excess heat (whether generated by the "furnace" or the environment) while conserving warmth when the environment is cold.

You can thank your hypothalamus, a gland buried deep in the brain, for keeping track of all of this. The hypothalamus gets signals from all over the body regarding temperature. If your body temperature is low, less blood flows to the skin; this prevents loss of body heat. You may start to shiver. This is your body's way of generating heat until you put on a coat or move to a warmer place or take some other action to warm up.

But, if your body temperature is rising, signals go to other areas of the brain that trigger you to take action (such as removing a sweater or seeking shade) to avoid overheating. Getting into water can also cool things down. Heat is removed as water evaporates from the skin. Sweating may get a similar result.

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Why Do Some People Feel Cold All the Time?

Have you ever noticed how some people feel cold while everyone else is comfortable? It could be due to an underactive thyroid, a gland that resides in the front of the neck and controls your metabolic rate.

Hats Off!

Here are some other myths:
  • You lose 50% of your body heat through your head.
  • Wearing a hat in cold weather saves body heat more than other clothing.

The skin and scalp of the head make up about 10% of total body surface. The heat lost from these areas are appropriate to that amount.

True, there are a lot of nerve endings around the scalp and face that make cold particularly bothersome. And it's true that when we're heading out the door in the cold, our heads are often the only thing uncovered. If that's the case, you will lose more heat from your head. But covering your head with a hat is no more important than covering other similarly sized areas of skin on the body.

"Cold intolerance" is a particularly common symptom of hypothyroidism. A simple blood test can screen for this hormone deficiency. So, if you have cold intolerance, let your doctor know.

Other conditions that may cause cold intolerance include:

  • Anemia
  • Anorexia nervosa or other causes of significant weight loss
  • Raynaud's phenomenon (in which the arteries of the fingers constrict more than normal in response to cold)
  • Diseases of the hypothalamus
  • Infections

But, most people with cold intolerance are healthy. It's just the way they are.

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Why Do Some People Feel Warm All the Time?

I keep my office thermostat at 68 degrees. My next door neighbor keeps hers at 58 degrees. (She complains about how warm my office is just walking past it!)

There's nothing wrong with her. She always feels warm so a cool office is more comfortable to her.

It shouldn't be surprising that the thyroid can be to blame for heat intolerance, too. But this time the problem is an overactive thyroid (hyperthyroidism). Other causes include:

  • Stimulant medications (such as amphetamines)
  • Anxiety
  • Coffee or other caffeinated beverages
  • Menopause (the lack of estrogen leads to hot flashes)

As is true for cold intolerance, most people with heat intolerance are healthy.

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The Bottom Line

Your body works hard to keep your temperature where it should be. When it's higher or lower than usual, your doctor can almost always figure out why and suggest treatment.

Yet, there's still much we don't know about feeling hot or cold, even when your body temperature is normal. It turns out that your favorite thermostat setting is just one more mystery that makes each person unique.

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