Before someone gets full-blow heat stroke, what are the body's early reactions to excessive heat?
Heat rash and muscle cramps are early signs of people being overwhelmed by heat. If those aren't dealt with, it can lead to more severe symptoms.

Cramping of muscles can be for a number of different issues, including electrolytes not getting to the muscles.

People should be aware that their skin turning red and dry are indicators that heat is impacting them.

Who is the most vulnerable to extended high temperatures?
We know the risk factors for dying from heat are urban dwellers who are elderly, isolated and don't have access to air conditioning. Obese people are at increased risk as are people on certain medications. And people who are exercising or working in the heat, who don't meet those criteria, can be at risk.

What medications can make the body more susceptible to extreme heat?
In the study from the 1995 Chicago heat wave, we found that diuretics for high blood pressure were some that did, and beta blockers—a number of studies showed that people taking them could be at increased risk.

There are some studies that have shown that certain mental health medications may impact a person's ability to deal with the heat. But that's a difficult one to get at. When you look at the number of people who die in a heat wave and the number of people who are taking those medications, the numbers can get pretty small pretty quickly.

What's the hottest temperature a healthy human can tolerate?
We don't know that—no one knows that. There are different humans, different humidities, different types of temperature.

Have we not evolved to cope with super hot weather?
Certainly society has evolved in dealing with the heat—and that has been in the development of air conditioners. The number-one factor that ameliorates death from heat is access to air conditioning.

And I've read that fans don't work to prevent overheating in really hot temperatures…
Not only does it not work, it actually makes it worse. We compare it to a convection oven. By blowing hot air on a person, it heats them up rather than cools them down.

Are modern humans neglecting to do something our ancestors did to survive the heat?
I think it's always been a problem. There's history over hundreds of years of people dying of heat. Philadelphia in 1776 had a major heat wave that caused deaths.

We're also living to older ages, and we're more urban now than we have been in the history of the human species. That intense crowding can combine with the heat island effect in big cities. Our elderly people are also more isolated than they have been in the past, so those factors can play a part, too.

The IPCC, the Intergovernmental Panel on Climate Change, the thing that they are most comfortable in predicting, that the science is most solid for, is the increase in many parts of the world in the duration and intensity of heat waves.

14 Comments

1. 1. tichead 11:44 PM 7/23/10

   I read something a few years back about a 'heat gene'. Sorry, I can't provide a link but I'm pretty sure it was in Sciam. Turn the gene on and H. sapiens can tolerate about 3 degrees F greater core temperature than average without damage.
   
   I live in the subtropics (95 F and 70% RH are normal from mid April to mid October) and work outside, usually in full sun, and drink about a gallon of distilled water each day. I wear light value cotton long sleeve shirts and long pants (T-shirts and shorts are for sunburnt bug bitten tourists). Cotton wicks out sweat and provides excellent evaporative cooling without the need for mosquito repellant and sunblock (icky, sticky chemicals on the skin). I live in an 80 year old house with no air conditioning, except for a window unit in the bedroom, (I like to sleep cold), and am quite comfortable. Five generations of ancestors have, for the most part, lived this way. Conversely, when the dry season temps get down into the forties and sometimes thirties, my body does not want to move.
   
   I didn't grow up in this climate, I moved around alot, born into and living mostly in northern climates with blizzards and freezing winters, and only got back to my 'roots' as an adult.
   
   Has my heat gene been epigenetically 'turned on' or, have I simply adapted as an individual to this climate? If I have simply adapted to this climate, then can anyone adapt to any climate? If so, then how long does it take for H. sapiens to acclimate to any given climate? Lastly, is there such a thing as a 'heat gene'?

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2. 2. Mark B 03:50 PM 7/24/10

   I find Mr McGeehin's comments about fans misleading. I used to work at sea, in a ship's engin-room (hot) without air conditioning, in the tropics with high humidity. With my skin and often my clothes wet with sweat, standing under an air blower could feel positively cold - at well over 100deg. All the while you are sweating, fans help cool you because the airflow increases evaporation. However, if you stop sweating and air temperature is above body heat, it will increase body heat. So, wet clothes and a fan will help cool you in high heat... Water and moving air is all you need, but you need them both.

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3. 3. tichead 10:56 AM 7/25/10

   Mark B: I had similar experience in a ships engine room. The coolest place was between the mains under the fresh air blower. Only problem was that the air volume was so great and moving so fast it would dry one off in a few minutes, clothes and all, so it was back to making rounds in the sweaty spaces then back to the blower.
   
   I am still curious about the 'heat gene'. Have any other readers of Sciam or similar mags heard of this or has the heat caused me to suffer dilusions?

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4. 4. doug l 12:58 PM 7/25/10

   I would guess that a warmer planet would be advantageous for our bodies as we are, according to the fossil record, evolved from tropical primates. Warmer planets have more moisture available and that, along with a longer growing season will create more food, and longer, cooler, climates are not all that good for us. The geological record shows that cooler periods coincide with the expansion of arid regions.

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5. 5. frgough 09:58 AM 7/26/10

   Ya gotta love how SA breathlessly reports June was the FOURTH hottest month on record.

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6. 6. andreanis 05:13 PM 7/26/10

   Yes in fact my friends this is an issue more research should be devoted to..let's remember that for the human body slight increases in temperature do mean a lot.And warmer summers seem to be more and more common:
   in my view research should aim at 1) study in depth the physiologic effects of heat on humans 2) elaborate new innovative technology in order to defend the population (if this phenomenon as it seems,keeps progressing.3) Size the opportunity:higher temperatures also mean more natural energy around.More research on how to convert this new opportunity (eg solar/photovoltaic/heat pumps or else should be done..) into useful civilian uses is something no to be missed..
   
   Join my discussion forum:
   
   http://health.groups.yahoo.com/group/HyperthermiaACLS/
   
   Andy

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7. 7. bongobimbo 05:25 PM 7/26/10

   There are some historical references to the mass deaths of Irish rebels sent to the West Indies to work in the cane fields in the 1700s. I never checked the reports (it's not my historical era) but they could be accurate. As a pale redhead growing up in Miami I went to the hospital twice for something the doctor called "heat prostration"--which seemed to be a combination of sunburn, windburn, 90%+ humidity and high temperatures. My symptoms were nausea, feeling faint (although I don't recalling ever passing out) and lethargy. My dad had many skin cancers down there and mom (naturally swarthy) got her first stroke after working outside in the garden. I agree there's something in the DNA that affects health in various climates. There are some climates, like south Florida's, that are hostile to such human beings. Now the humid heat is creeping north.
   
   I do use fans a lot--my great aunts' advice not to open any windows on very hot days, but run the fans since it was bound to be cooler inside than out (both lived healthily to 96 in hot southern Iowa). To that I add running the A/C and fans together for a couple of hours, then using only fans for as long as tolerable and drinking lots of water and iced tea. But what about sodium chloride salt? Normally I avoid it and use potassium chloride instead. NaCl tends to give me edema of the ankles in extreme heat. Yet--I've known people hospitalized with "salt deficiency" on hot days. NaCl? Or KCl? Or both? I wish that the writer had discussed the role of salt in heat-related illnesses.

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8. 8. ecoligist 06:20 PM 7/26/10

   I've heard that excessive heat disrupts the sodium/potassium balance and maybe of other ions that are critical to nerve transmission - cramps, and distorted thinking. Of course, the body can only stand so much of this disruption before the lethal threshold is reached.
   
   This would account for the efficacy of diuretics which affect the Na/K balance.

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9. 9. marcellesilbert 12:55 AM 7/27/10

   In Perth, Australia we have heat waves in the 40's (Celcius) 100's (Farenheit) and it gets bad. We use a fan because it causes evaporation of sweat and makes you feel cooler. If we followed your advice to not use fans there'd be a lot more dead people. Has Katherine Harmon ever tried using a fan in hot weather?

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10. 10. andreanis 04:12 AM 7/27/10

    Good day Bongobingo..actually I think you are bringing up here an interesting point ie "what can be done to work more efficiently at higher temperatures" ..I did a small internet search and I found this intersting link http://www.cdc.gov/niosh/hotenvt.html
    regards
    Andy

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11. 11. Jim Lacey 03:36 PM 7/28/10

    At Fort Sill in 1957 in the desert heat we fledgling lieutenants were allowed to bring jugs of ice water into the field--not standard issue. Also, we were instructed to take salt tablets with meals. The one benefit of this dehydrating heat was that beer never again tasted as good at the first one after coming in from the field!

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12. 12. Quinn the Eskimo 03:58 AM 7/29/10

    Too much algore can kill anyone. Ask Tipper.

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13. 13. andreanis 03:07 PM 7/30/10

    no doubt electrolytes are messed up by eat ..just think of the lost sweat

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14. 14. AvaMaru in reply to doug l 08:53 PM 7/15/12

    I think growing temps on the planet are horrid for our survival. I live in a little podunk town in northern illinois, summers have been about 115 degrees F. Higher temperatures were the leading cause for giant reptiles which rely on heat to grow. scientists have found bones of a 48 ft long snake, and table sized turtle shells. This was back when they thought the leading cause was climates of temps in the 90s. If that's the case, that little anaconda in your yard can become a human-eating monster...
    also, i don't think we could adapt. The climates change so quickly in the course of 10 years our summers could be from 83F average to 110F average, and our insides cannot handle that kind of change :(

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