By Public Service Associate Autumn
Everyone knows that humans (unlike much cooler reptiles) are warm blooded, or homeothermic.1 Our bodies try very hard to keep us at one consistent temperature, normally about 98 degrees. Even a four degree change in body temperature in either direction can cause us irreparable harm and a spiral into death. Understandably, this means that humanity has a pretty universal “comfortable” living temperature, between about 68- and 77-degrees Fahrenheit,2 where maintaining your core temperature isn’t too metabolically taxing. Despite this, humans live in basically every ecological niche there is, from Siberia and Northern Canada to the Sahara. Some of this adaptability is technological,3 but a fair amount of it is our bodies’ astonishing ability to cool us off and heat us up. What’s most interesting, to me at least, is how the body does this and what happens when those adaptations fail.
It’s common knowledge that humans sweat to cool down. As you sweat, your body pushes more blood toward your skin, so that as the sweat evaporates and dissipates heat, the blood is also cooled. Then the cooled blood is circulated through the body and your core temperature drops. We know this thanks to a British physician, Charles Blagden, who in 1775, did what people who are bored do; he tried to cook himself. (I jest, please don’t do that if you’re bored). Specifically, he built a room that acted as a giant oven to test how long he, several of his friends and a dog, could stand the heat.
The group started at 100 degrees Fahrenheit and made it up to more than 200 degrees Fahrenheit, with one participant, Joseph Banks, managing to stand in 210-degree heat for three minutes.4 More interestingly, Blagden discovered that no matter how hot the room got, his and his friends’ body temperatures never rose beyond a few degrees.5 They measured this by taking the temperature of their pee immediately after exiting the room. Blagden, from these experiments, worked out that it was sweat that was cooling the body and helping to maintain a consistent temperature.
Blagden’s study has been supported by modern experiments. In one interesting case, an athlete ran a marathon on a treadmill as the room temperature went from negative 49 degrees to 131 degrees Fahrenheit. During the run, despite the exercise and the extreme temperatures, the athlete’s core temperature shifted less than a degree.6 Which is an astonishing feat to think about.
As those experiments prove, sweating is a very efficient tool to cool us down– up to a point. If you don’t get too hot too fast or can quickly get to a cooler place, nothing goes wrong. But if you can’t, your body has no alternative cooling methods. It will keep circulating blood faster and faster, trying desperately to cool itself down. But this speeds up your heart, and thus your metabolic rate, which makes you even hotter.7 It also risks too much blood being pulled away from your organs, specifically the brain, heart and kidneys, denying them sufficient oxygen.8 At this point, you will likely fall down, due to dropping blood pressure and then, at about 105 degrees, begin to have seizures.
What’s even more interesting, though, happens when you hit 107 degrees. You quite literally break down at a cellular level.9 Your cell membranes dissolve and the proteins inside those cells begin to unravel, leaving them unable to “extract energy from food…. fend off invaders, destroy waste products, and so on.”10 Your body is melting on the inside. That includes holes forming in your intestines, releasing toxins into the bloodstream. Normally, the body still has enough control to clot your blood in response to these toxins. But that actually doesn’t help you. The body will use all the remaining clotting proteins to stop the toxins; as a result, you internally hemorrhage everywhere else, and die. Not even immediate medical assistance can save you.11
Freezing to death is, as best as I can discover, a lot less molecularly interesting. Probably because you do not actually have to freeze in order to die from the cold. In fact, while it is rare, people can die in 30 to 50 degrees Fahrenheit.12 All that’s required is for your body temperature to drop below about 70 degrees.
As with cooking to death, freezing is a process. When you first start to feel cold, your body constricts your capillaries and pulls blood away from the skin and in towards your organs. In mild circumstances, this is what gives you goosebumps. This serves both to ensure your organs stay warm and to attempt to reduce the heat you lose to the air. You will start to shiver, which is your body trying to generate more heat by violently constricting all your muscles, normally when your core temperature drops to 95 degrees. And it just gets worse if you cannot warm up. At 86 degrees your heart can no longer pump its normal amount of blood around the body, and your brain becomes oxygen starved, sometimes resulting in hallucinations. At 82 degrees most people will pass out and at 70 degrees, your organs fail, and you die.13 Ironically, even if you are rescued at some point in this death spiral and warmed back up, you can still die. Even a slow warming can shock your heart or other organs into sudden failure.
Just so you don’t think the cold pales in comparison to heat in all the ways it can damage you, let’s take a brief foray into frostbite. I mentioned that your extremities lose heat faster than your core. Both because your body actively pulls back the blood from those areas, and because your fingers and toes have a lot of surface space and very little mass– the ideal way to vent heat.14 This also makes them the most likely place to get frostbite, along with your ears and nose. Frostbite occurs when parts of your body actually freeze. The water inside your cells crystallizes, and if allowed to get bigger, those ice crystals will break the walls of your cells, permanently damaging your flesh.15
However, some people, particularly people who live and work in the extreme cold like Innuit hunters or Norwegian fishermen, can periodically increase the blood going to and from their hands. Termed “the hunter’s response” by the man who discovered it, this periodic reopening of the capillaries to the hands, feet or even nose, can increase temperature there more than ten degrees before cooling down again.16 As this trait displays in a select number of individuals, scientists don’t know if it is something that people acclimate and do, or if it is genetic and those with it self-select for jobs in the extreme cold.17
You might be wondering at this point why I’m telling you all of this. Mostly, because I find it interesting. Who doesn’t like to know exactly how they could die? And I didn’t even get into the diseases bugs can give you, bugs that are becoming more rampant as the Earth heats up.18 But also, because it helped me to better understand how the body works, and how much more impressive humanity’s ability to survive all over the planet, and I wanted to share. So, if you’re still curious, here are a few books to explore.
Book List
- The Body by Bill Bryson Book | eBook
- The Heat will Kill You First by Jeff Goodell Book | eBook
- Fire Weather by John Valiant Book | eBook
- Out Cold by Phil Jaekl Book
- The Icepick Surgeon by Sam Kean Book | eBook
- Stiff by Mary Roach Book | eBook
Footnotes
1And even this statement is misleading as birds are technically a branch of the reptile family tree, and they are homeothermic. Homeotherm, according to the Oxford English Dictionary, is “an organism that maintains its body temperature at a constant level, usually above that of the environment, by its metabolic activity.”
2Though apparently people sleep best at a cooler, 60-to-67-degree temperature.
3Igloos can be up to 70 degrees warmer than the outside temperature. https://www.transun.co.uk/blogs/how-does-an-igloo-work
4The Body by Bill Bryson, pg. 187; To prove the thermometers weren’t off, Blagden felt the need to place beef and eggs in the room with the participants, which promptly cooked. And all of the participants had to wear some form of clothing, so their skin wasn’t burned.
5https://publicdomainreview.org/collection/experiments-and-observations-in-a-heated-room-1774/
6Bryson, pg. 186 and 187
7As Jeff Goodell, author of The Heat Will Kill You First, puts it, “As your internal temperature rises, rather than cranking up your air conditioner, your body fires up your furnace.” pg. 40-41.
8Goodell, pg. 40
9Formally, you ‘denature’.
10 Goodell, pg. 41
11Goodell, pg. 41
12People normally have to be wet for a long period of time for that to happen, as the body loses heat 23 times faster through water than through the air. https://www.livescience.com/6008-person-freeze-death.html
13https://www.grunge.com/614991/what-really-happens-to-your-body-when-you-freeze-to-death/
14https://onlinelibrary.wiley.com/doi/full/10.1111/j.1549-8719.2011.00126.x
15Your cells are being stabbed to death. From the inside.
16 https://www.outsideonline.com/2152131/freezing-death
17https://onlinelibrary.wiley.com/doi/full/10.1111/j.1549-8719.2011.00126.x
18Maybe I’ll make that my next blog post.