What happens when you’re getting too cold?
Updated July 2020.
When we say “cold”, we usually mean one of two things. The first is the oddly delicious foot-stamping, hand-rubbing, nose-blowing kind that millions of us Brits experience less and less frequently these days, as we trudge through the slush, or curse when the snow billows in our opened car doors.
And then there’s the other kind.
You can be sure you’re at your optimum core temperature because you’re lucid and conscious. In fact, your ongoing survival is dependent on it, on hovering somewhere near 37°C every single day, for the rest of your life. Stray above or below more than a little, and you will start to die.
Luckily, you’re amazing. You’ve been fitted with an incredible piece of biotechnology, a kind of super-advanced thermostat called a hypothalamus. This almond-sized marvel, buried deep inside your brain, is why you’re alive today. Take a moment to say thanks. (I’ve just thanked mine).
Your hypothalamus performs a range of invaluable and breathtakingly elegant roles, but the one we’re giving thanks for is the maintenance of your good self as a homeotherm – an animal with a steady core temperature usually above that of its surrounding environment. Thanks to your thermoregulatory system (heroically led by the hypothalamus), you never need to worry too much about keeping just the right temperature – your body’s got it covered.
It takes a lot to overwhelm your hypothalamus’s capacity to keep your core temperature stable. But once it’s achieved, the effects are rapidly catastrophic.
So let’s chill out a little and see what happens.
37°C (subzero-temperature air exposure)
There’s a dark little truth about your hypothalamus – it doesn’t care if you’re feeling cold on the surface. All that matters is what’s going on inside. So when the wind-chill starts savaging your exposed flesh, your capillaries squeeze the blood out of your skin, driving it inward where it can assist in maintaining your core temperature. Your paled, cracked, pinched extremities are being offered up for sacrifice – and unless you’re one of the lucky few who has a natural hunter’s response, it’s gonna start to hurt.
What’s the common response to a surface chill? Vigorous exercise of the flexing, stamping, wiggling kind, and a tendency to increase your pace of movement. This works a treat in the short term, burning up inner stores of energy and elevating your overall body temperature until you’re comfortable again.
The contrast is delicious, so you keep moving, keep burning up – until you start to sweat. Sweat cools (that’s its job) and before you know it, you’re clammy with freezing perspiration that drags your temperature lower and lower. Worse still, your skin is too cool to efficiently evaporate the sweat away, so it clings on, sucking the heat from your bones. (This is why moisture-wicking garments are quite literally lifesavers).
One degree down, and boy do you know it. Your muscles are tightening up (more formally, you’re experiencing pre-shivering muscle tone). It’s a forerunner of the muscle contractions that are shortly going to make you a clumsy invalid. Now’s the time to adjust tricky straps and tie shoelaces – another core temperature drop and you’ll be a juddering, uncoordinated mess.
You’re a juddering, uncoordinated mess. As mild hypothermia sweeps through your body, your muscles leap to your defence with frenzied high-speed involuntary contractions, better known as shivering. Exercise generates heat – but with an unfortunate flip side. To spasm so violently, those muscles require an increased supply of blood – and so shivering can accelerate the rate of cooling at your core.
Plus, it’s horribly unpleasant. All your muscles have already tightened up, and now they’re shaking as well. This applies to all your muscles, even those around your eyes. Your basic senses are starting to go…
…but strangely, you don’t care. Your body is responding logically and sensibly by hoarding its resources and making itself slower and smaller in every way it can (this may save your life later on) – and the effect right now is to dull your thoughts, drugging you into apathy and then a stupor. Whatever. Yawn. A little sleep before you get back to fighting the cold is just what you need, surely?
Shivering hasn’t worked, so your body abandons it. (This helps you doze off). Your oxygen consumption has dropped significantly and your oxygen-starved brain is struggle to string a thought together – other than “I really need to pee“, thanks to all the inwardly-pushed body fluids flooding your kidneys.
If a loved one rescued you right now, you wouldn’t be able to recognise them.
Your heartrate is becoming arrhythmic, further restricting the amount of oxygen reaching the brain. Time for Harvey to make an appearance. In your stupified, thermal free-falling state, you’re hallucinating wildly. You probably think you’re being rescued. But then …
…you’re suddenly on fire. It’s a bleak irony that as you freeze to death, there comes a point where your skin feels like it’s alight, prompting you to struggle out of your clothes. This is called paradoxical undressing, and may happen because your ailing hypothalamus pops a fuse – or because it tries a last-ditch attempt at warming you, flinging all your capillaries open and giving you the mother of all full-bodied blushes. You’ll also feel the urge to crawl into a small space (terminal burrowing), a mechanism that often makes it harder for rescue parties to find severe hypothermia victims. This is not the finest hour of your survival instincts.
28°C and below
You’re down – but not necessarily out. Your skin may be blue and cold, your pulse indetectable and your heart may be beating too slow to keep you alive under normal circumstances…but these are not normal circumstances. Remember that your entire body has slowed down as you cooled, including the most critical part of it, your brain. Your oxygen supply is way down – but so is the demand for it.
You’re not dead: you’re suspended between life and death. Or put another way, “you’re not dead until you’re warm and dead.”
Now the key to your survival is rescuers who know how to revive you. If they warm you too quickly, this delicate balance between supply and demand will be broken and you’re history.
In “rewarming shock,” the constricted capillaries reopen almost all at once, causing a sudden drop in blood pressure. The slightest movement can send a victim’s heart muscle into wild spasms of ventricular fibrillation. In 1980, 16 shipwrecked Danish fishermen were hauled to safety after an hour and a half in the frigid North Sea. They then walked across the deck of the rescue ship, stepped below for a hot drink, and dropped dead, all 16 of them.
– Peter Stark, Outside Magazine, 1997.
If you don’t fancy trusting your life to the specialist medical knowledge of the first bunch of people (probably strangers) to stumble across you…I don’t blame you. Ask yourself: what would your first instinct be if you found someone almost frozen to death? Warm them up as quickly as possible? Me too.
So keep yourself well-wrapped, plan journeys in advance, keep warm…and put your trust in the thermostat inside your head. After all, it hasn’t done a bad job this far.
- “The effects on cold on the human body (with special reference to South African coldstores” – James Cunningham, October 2009.
- “As Freezing Persons Recollect the Snow – First Chill – Then Stupor – Then the Letting Go” – Peter Stark, Outside Magazine, January 1997.