What happens when we get too hot?
Being alive is a remarkable balancing act between two cliff edges. When the temperature drops, we’ve only got a 10 degree margin of safety, a few paces backwards, before we’re feeling the icy touch of death. But this leeway is luxurious compared with what happens when we start overheating. Here at our normal body temperatures, at 37 degrees Celsius / 98.6 degrees Fahrenheit (or thereabouts), our toes are already poking over the edge of our very own heat-deaths.
Because right now, all that separates you and runaway thermal meltdown is…
Let’s apply a little heat and see what happens.
37.8°C / 100°F
Maybe you’re in a nice warm room, and you’ve just had a big meal. You’ve got a bit of a glow on. This is because our bodies are amazingly efficient at converting food into heat – so much so that if left unchecked, your metabolism would push your core body temperature around 1.5° C higher every hour. Two hours and you’re approaching done.
But yet again, your hypothalamus is here to haul you out your own fire. As soon as you started straying above optimum temperature, it triggers two notoriously unloved bodily processes for venting heat. Your skin’s blood vessels dilate and blood rushes up and into them – and that blood is being pumped straight from the hot zone, so when it meets the coolness of the outside air, the unwanted heat is safely pushed out your body. That’s why a flushed face feels sizzling hot.
But far more embarrassing – and more marvellous – is when tiny glands all over your body start squirting out droplets of water mixed with sodium, potassium, calcium, magnesium and a host of trace minerals. You’re doused by your own sprinkler system, a warm liquid that immediately cools on contact with air (for “cools” read “transfers heat off the body and into the air”) and then evaporates, shifting remarkable amounts of heat in the process.
An amazing biological achievement…which we hate. Nothing like a big sweat patch to flag up to the world that you’re a repulsive nerd – even though it’s actually a small sign that Darwin’s dice are rolling in your favor. You pull your clammy shirt away from your body and fan it surreptitiously. Ugh – human beings are so gross.
38°C / 100.4°F
Maybe you’re newly arrived in an equatorial country you’ve never visited before. And maybe you’ve just tried to carry two suitcases up five flights of stairs. You’re in great shape, and under normal circumstances this physical feat would literally be no sweat. But these aren’t normal circumstances.
As wonderful as the hypothalamus is, it’s not fitted with a GPS. It doesn’t know you’ve just arrived somewhere that’s on average 25 degrees warmer at this time of year. In fact, if your thermoregulatory system could be confused, it’d be thoroughly nonplussed by now. Why isn’t a mild sweat doing the job? Why isn’t turning you lobster-red achieving the required cooling results? You’re suffering from a kind of thermal jetlag, and your body needs time to acclimatise. Until then, sorry: you’re going to sweat buckets. The floodgates are open.
This is a sensible cooling mechanism in the short term – but you’ve got to do your bit to help it. You’re like a breached dam, losing massive amounts of fluids and salts, and if you don’t keep both of them topped up you’re going to lose the fuel you need to keep you alive. So, lots and lots of water. Go nuts. No, really.
But you’re also going to need to replenish some of those body salts, mostly that sodium that’s crusting nicely in the wrinkles of your skin. You know what you need? Salty snacks. Yes, it’s medically important that you eat dry, prepackaged junk food (which will even make you thirstier, making you drink even more water). Oh, life is a struggle.
38.5°C / 101.3°F
Whoops. For your own good suicidally stupid reasons, you’ve decided to sip a strong coffee instead. It’s probably a myth that caffeine itself dehydrates you (it can increase your rate of urination, but usually not enough to derail your fluid levels). However, a strong coffee will psychologically slake your thirst for a short while. This is Bad. You’re sipping fluids when you should be gulping them.
Now it’s time to start your meltdown.
Your skin is painfully hot to the touch…but it’s drying up. This is because you simple can’t perspire enough, and your body heat is scorching away what little sweat you’re managing to squeeze out. Your lips feel swollen, and your face is a truly livid lick of scarlet. With your blood so close to the surface of your skin, it’s losing its water due to evaporation – which means it’s thickening. Thickened blood? Clotting. Your chances of suffering a stroke or a heart attack just spiked.
Don’t go standing up suddenly. Your brain needs a regular blood supply – around 15% of your cardiac output. With so much blood currently diverted elsewhere, your blood pressure is dropping and not enough is being pumped up to your head, making you woozy, nauseous and unable to stand without waves of dizziness. You’re becoming severely hyperthermic – the warm-blooded twin of hypothermia.
But don’t worry – you won’t be conscious for much longer.
39.5°C / 103.1°F
You’re scared and in pain. Your breathing and your pulse are both racing. You’re also yawning convulsively. Your brain is in trouble, and it’s forcing you to suck in cool air and the oxygen you need to keep conscious in your elevated metabolic state.
Are your surroundings helping or hindering your last-ditch attempts to save yourself? If the air around you is almost as warm as you are, your sweat can’t evaporate…which is why heat exhaustion is such a danger in high-humidity (75%+) environments, especially to unacclimatised new arrivals.
At this stage, you might be panicking. Hopefully you’re knocking back as much water as you can – and that would be a great idea if you kept snacking too. Dilute your body’s saltwater mixture too much and you’ll be hit with a bout of hyponatremia. Symptoms? Same as those from heat exhaustion – except with the thrill of possible brain swelling. It could well be that the only thing between you and a coma right now is a tube of Pringles.
40°C / 104°F
Welcome to the death zone.
If you’re still conscious at this temperature, your awareness is severely impaired. You’re almost certainly not going to do the right thing – and the right thing is to get your temperature down as quick as possible, because you’re starting to die. Beyond 40 degrees Celsius, you’re into heat stroke.
This is ugly. Your hypothalamus can’t do anything. Your core body temperature is rising, your natural thermoregulatory functions can’t do a damn thing to stop it, and your body tissues are suffering permanent damage as a result.
Your one and only hope right now is for medical services to arrive and cool you with specialist equipment. If well-meaning samaritans lay wet towels on your skin, it’s probably only going to be a few seconds before the damp material warms and becomes an insulator. Fans blowing cooler air, periodically-applied cold compresses, water and a little salt…this is how passers-by can keep you alive until professional help arrives. But you can’t tell them that because you’re now unconcious, just minutes from a coma.
Heat stroke isn’t necessarily fatal – if treated swiftly and skillfully. But even if help arrives in time and your temperature is brought down to safe levels, it could be months before it’s known how much damage has been dealt to your organs.
42°C / 107.6°F
Your last shot at salvation is gone. You’re boiling in your own skin.
And here’s how. Your body temperature is so elevated that the proteins in your cells are cooking – as Alok Jha puts it, “like egg white as it boils”. Muscles are starting to lock up – including the ones that allow you to keep breathing. Your thickened, low-pressure blood supply can’t reach your brain…
Your brain, the nerve centre of your body, shuts down.
- “Boiled Alive” – Alok Jha,The Guardian, 26th July 2006.
- “Avoiding Heat Illness” – Dr. Gary F. Arnet, Backwoods Home Magazine.
- “After Heatstroke, When Is It Safe To Exercise?” – Gina Kolata, New York Times, 14th June 2010.
- “Heatstroke” – Robert S. Helman M.D., eMedicine.