Heat regulation: How your body keeps you from getting too hot

by James Hubbard, M.D., M.P.H.

Summertime comes with lots of tips on how to stay cool. But for you how-stuff-works buffs out there, here’s the science behind why those tips work.

First, some basics on your body and heat.

  • Heat is energy and is generated.  Cold is not generated, but is the absence of heat.
  • Your body generates heat from metabolism even while you’re at rest (called the basic metabolic rate or BMR).  In fact, it usually creates more than you need.  Mechanisms explained below regulate you around 98.6 F.
  • You generate as much as three to six times more heat with exercise.
  • Just resting in the hot sun can increase your BMR 50 percent more than resting in the shade.
  • Stimulant drugs like amphetamines and cocaine also cause you to generate more heat.

Now, here are the whys behind some of the dos.

DO: Watch what you’re sitting on—and if somebody faints, be aware of their lying area too.
WHY: Conductive heat exchange.

Conductive heat exchange transfers heat between two nongaseous surfaces.  It’s not usually a factor since only the small surface of you feet or hands is in contact with another solid surface and you avoid objects too hot.  It can be significant if lying on a cold or hot surface with altered consciousness.

DO: Wear loose, breathable clothing—but don’t count on it.
WHY: Convection.

Convection transfers heat from a surface (your body) to a gas or fluid like air or water.  Typically the higher the difference between the body and the air or water, the faster the transfer.  Wind can also play a role, but once the air temperature rises to close to skin temperature, transfer is minimal and wind can’t help.  Of course, air temperature hotter than skin transfers heat to the body.  Loose, breathable clothing makes air transfer easier.

DO: Find shade.
WHY: Radiative heat exchange.

This involves electromagnetic waves (radiation energy) from the sun and your body and accounts for half of heat transfer.  Clouds and clothing decrease the radiative sun heat, as does the sun’s position in the sky.  This is a good reason to stay in the shade when the sun is at its highest.

DO: Drink so you can sweat.
WHY: Evaporative heat exchange.

Sweat evaporation removes heat from the skin.   The body adds a little sodium chloride (salt) to the watery sweat to speed up evaporation.  The more humidity in the air the harder it is for the sweat to evaporate.   Also remember sweat dehydrates you.  You must replace the lost fluids by drinking to maintain the sweat process.

Our body uses receptors to detect when we’re getting warm.  They trigger sweating to cool the skin.  But blood is also involved in this process.  Blood vessels in the skin dilate (open up) blood flow there as much as 30 times more.  The hot blood from the core body organs travels to the cool skin surface to convect heat.   The cooled-off blood then goes back to the core organs to pick up more heat and the cycle continues.

These mechanisms don’t work as well in infants and older people, making them more susceptible to the heat.

Surprising Fact: Within 15 minutes in the hot sun a closed car’s temperature can reach 140 degrees F.

For more summer safety tips, including what those weather warnings mean and how to avoid heat exhaustion and heat stroke, check out this article. In my next post, I’ll attempt to explain how everyone must have a few days to acclimate to a rise in temperature, no matter how tough you are.

What are your tips for staying cool?

Doctors and business owners: Send customized issues of My Family Doctor to your customers or patients. E-mail publisher-at-familydoctormag.com for details.

As with all information on this site, this article cannot replace professional, personal medical advice. Read more here.

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4 Responses to “Heat regulation: How your body keeps you from getting too hot”

  1. Sagan Says:

    Uh oh. Now that this is out there, the new fad diet will involve sitting in the hot sun to burn more calories! :)

    It’s still really cold around here- so I guess I better kick the exercising up a notch to stay warmer. Not a bad reason to do so!

    Sagans last blog post..Guest Post: The Transformation to a Warped Body Image

  2. James Hubbard, M.D., M.P.H. Says:

    Sagan, didn’t think of that.

    It’s still a little cool here in Colorado Springs also.

    James Hubbard, M.D., M.P.H.s last blog post..Smart Balance Peanut Butter: Expert review – plus readers’ opinions

  3. Judy Rodman Says:

    This is great info for artists who are singing and playing in extreme heat this summer… I’ll pass it on!

    Judy Rodmans last blog post..ALERT:PPP vocal workshop at Indie Connect Monday night (June 8th)

  4. James Hubbard, M.D., M.P.H. Says:

    Thanks Judy.

    James Hubbard, M.D., M.P.H.s last blog post..The Secrets Doctors Don’t Tell You About Prescription Medicine

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