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This is a question that has been in my mind since I was a kid. I'm not a doctor, nor even a biology student, just a curious person. What is the minimum and maximum temperature a human body can stand without dying or suffering severe consequences (eg. a burn or a freeze)? While at this subject, how much more global warming will the human body be able to take? Seeing as temperatures keep on rising, I'm just wondering how much longer until the temperature starts having drastic effects.

In my country the temperature is about 35-40-45 degrees Celsius in mid-summer (I live in Romania, eastern Europe, and the climate is supposedly ideal here) which is very unhealthy. Does the human body suffer more and more as the temperatures change?

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Better to say climate change. "global warming" implies that eveywhere on Earth will heat up due to increasing atmospheric CO2. This is not necessarily the case. We will see be seeing regional variations some of which may even include localised cooling, greater precipitation etc. –  Poshpaws Jan 11 '12 at 12:14
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Why would 35-40 degrees in mid-summer be unhealthy? It's way hotter in many part of the world... –  nico Jan 17 '12 at 18:21
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@nico, have you even read my post? Have you ever been to Romania? The climate is soposed to be ideal with a maximum of 28 degress in mid-summer. It's in the paranthesis. –  Bugster Jan 17 '12 at 20:15
    
@ThePlan: you can say that it is uncommon for Romania, sure, still I don't see how it is unhealthy... are people getting sick because of that? –  nico Jan 17 '12 at 20:33
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Yes, what people are describing in these answers are pretty similar. People faint on the streets here in my country, they report heart issues and the enviroment itself suffers, I watched the asphalt melt beneath the wheels of a bus a year ago. It's a very rough place. –  Bugster Jan 20 '12 at 17:39

4 Answers 4

up vote 19 down vote accepted

Hypothermia (when the body is too cold) is said to occur when the core body temperature of an individual has dropped below 35° celsius. Normal core body temperature is 37°C. (1) Hypothermia is then further subdivided into levels of seriousness (2) (although all can be damaging to health if left for an extended period of time)

  • Mild 35–32 °C: shivering, vasoconstriction, liver failure (which would eventually be fatal) or hypo/hyper-glycemia (problems maintaining healthy blood sugar levels, both of which could eventually be fatal).
  • Moderate 32–28 °C: pronounced shivering, sufficient vasoconstriction to induce shock, cyanosis in extremities & lips (i.e. they turn blue), muscle mis-coordination becomes more apparent.
  • Severe 28–20 °C: this is where your body would start to rapidly give up. Heart rate, respiratory rate and blood pressure fall to dangerous levels (HR of 30bpm would not be uncommon - normally around 70-100). Multiple organs fail and clinical death (where the heart stops beating and breathing ceases) soon occurs.

However, as with most things in human biology, there is a wide scope for variation between individuals. The Swedish media reports the case of a seven year old girl recovering from hypothermia of 13°C (3) (though children are often more resilient than adults).

Hyperthermia (when the body is too hot - known in its acute form as heatstroke) and is medically defined as a core body temperature from 37.5–38.3 °C (4). A body temperature of above 40°C is likely to be fatal due to the damage done to enzymes in critical biochemical pathways (e.g. respiratory enzymes).

As you mentioned burns, I will go into these too. Burns are a result of contact with a hot object or through infra-red (heat) radiation. Contact with hot liquid is referred to as a scald rather than a burn. Tests on animals showed that burns from hot objects start to take effect when the object is at least 50°C and the heat applied for over a minute. (5)

Freeze-burn/frostbite, which is harder to heal than heat burns(6) occurs when vaso-constriction progresses to the degree where blood flow to affected areas is virtually nil. The tissue affected will eventually literally freeze, causing cell destruction. (7) Similarly to hypothermia, frostbite is divided into four degrees (that can be viewed on Wikipedia).

As to the matter of global warming cooking us to death, I would imagine that it would be more indirect changes that got us first. If the average temperature had risen to the necessary 40°C to cause heat-stroke, sea levels would have risen hugely due to the melting of the polar ice caps. Crops and other food sources would likely be affected too, therefore I don't think that global warming is overly likely to directly kill humans.

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Hey, thanks for the answer. That pretty much sums it up. –  Bugster Jan 9 '12 at 6:31
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I don't think this is a good answer. Atmospheric temperature is being confounded with internal (body) temperature here. If the atospheric temperature in Romania is 45 C, you will not die (even given a fatal temperature of 40 C), because your body can thermoregulate (up to a point). Plenty of populations have existed for millennia where temperatures routinely exceed 40 C. –  kmm Jan 9 '12 at 23:12
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I should clarify that I think this is a good answer to the question: "What is the range of internal body temperatures at which a human can survive?" –  kmm Jan 9 '12 at 23:23
    
I do believe that though temperature above 40°C is alarming many children survive it when they are ill. –  Tomáš Zato Jun 20 at 7:01

As Rory explained, internal body temperature needs to be highly regulated.

Sweating is the main built in mechanism for removing excess heat from the human body. According to my biology book, in (100%) humid conditions humans cannot survive in heats of above around 45C, but in a dry environment can survive in heats of over 100C just through sweating.

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Yes, we can survive temperatures above 100 F (38 C) but surviving such temperatures requires continuous fluid intake. Since sweat evaporates quickly in an arid (dry) environment we tend to be unaware of how much water we're losing. This leads to heat exhaustion, then heat stroke, then death. Survival time depends on how well hydrated you are and whether or not you can replace the lost fluid.

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Can you add a reference to the statement on continuous fluid intake (and in what range it is valid)? –  fileunderwater Oct 21 '13 at 9:10

Some 200 years ago Dr.Charles Blagden, then secretary of Royal Society of London, went into a room that had been heated to a temperature of 126 degree Celsius ( 260 Fahrenheit) , taking with him a few friends , a small dog in a basket and a steak.The entire group remained there for 45 minutes. Dr.Blegden and his friends emerged unaffected.

This shows the power of homeothermy.

Source : Helena Curtis ( 5th edition) Chp. 38

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protected by Chris Jun 19 at 22:12

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