As I write, record cold temperatures are deep freezing the Midwest. There are stories everywhere about not being able to survive for even minutes out there! While much of it is internet hype, it’s obvious that cold weather does have some significant dangers. Let’s look at what the problems really are.
Keep in mind I am not a physician and am not giving you medical advice. I’m passing along what the Wilderness Medical Society has to say on the topic.
Frostbite can hit quick, but only in deep cold
Frostbite is when tissues literally freeze. Therefore, you can’t get it unless the body part is subjected to temperatures lower than 32 F, 0 C. Realistically, the tissue temperature has to be closer to 0 F, because the salts and other particles in your fluids make it harder for water to freeze. Wind chill does promote the freeze, though.
In frostbite, ice crystals form in the cells and blood, tearing up the tissues from the inside.*
Timing: Exposed skin freezes solid with just a few minutes of exposure to very deep cold, particularly if it’s wet and wind-exposed. Whole hands and feet can freeze with longer exposure times.
Recognize frostbite: Frostbitten tissues lose color, feel completely solid, and have no sensation or ability to move. If the body part is pale and numb but doesn’t feel solid, what you’ve got is the much less dangerous frostnip. Just warm the part up (you’ll feel the burn) to solve the problem.
Treatment: There’s a more full treatment on how to deal with frostbite here, but the basic plan is to get the tissue thawed in ways that don’t invite additional damage. In particular, the thawing tissues are sensitive to heat injury and won’t be able to feel when they’re getting too hot. It will be a long while, perhaps weeks, before it’s clear how much of the damage is permanent. Don’t thaw the tissue if you’re still in the cold and refreezing in the foreseeable future is a real risk. (1)
Hypothermia is when your core gets cold
When your core body temperature drops too far, you’re hypothermic. Nothing could be simpler, right? Not really. There’s a lot of misconceptions about hypothermia. It’s got its own post here that goes into more detail, but lets visit the highlights now.
One can get hypothermia in temperatures well above freezing. There have been cases of fit young men dying in 50 F weather when they were kept wet for too long. Water removes your body heat much more efficiently than air, so even water that feels ok for a brief swim can eventually kill you through hypothermia.
A few years ago, a couple of Navy Seal trainees died of hypothermia — in a Florida swamp. Water steals heat.
Timing: It takes a while to lower body temperature enough to produce hypothermia. You can’t develop it walking across a parking lot without your coat, no matter how cold the air. You can get it in just a few minutes if immersed in ice-cold water, but normally it takes much longer. Hypothermia can sort of creep up on you, as coping mechanisms fail when you become tired, dehydrated, or low on energy reserves.
Recognize hypothermia: Well … you feel cold. Then you start to shiver. As you chill further you stop shivering, but that’s a bad thing; shivering is an important heat production mechanism. Side note: Babies can’t shiver; their nervous systems aren’t fully organized. Don’t fall into the ‘Must be fine, she never started shivering’ trap.
Severe hypothermia can markedly resemble dead. No pulse, no respirations evident. Don’t despair though; there have been some amazing resuscitations after hypothermia if followed by careful rewarming. The emergency med saying is “They aren’t dead until they are warm and dead.” While frostbite may co-occur, it also might not; so the stiffness of frozen tissue is a poor guide.
Treatment: Rewarming, of course, but how you do it is important. You want to warm the core of the body before warming the limbs. If the limbs get warm first, blood starts circulating between them and the core again; and the blood from the limbs is often cool enough to chill the core further. That can actually kill the person. So, the Wilderness Medical Society suggests warming the core first (with warm bottles, gentle chemical warmers, or even some generous soul’s body heat) while the patient is kept lying still. (2)
Cold injuries, in summary
Frostbite tends to occur more quickly and locally. Hypothermia is usually slower, but poses the greater overall threat and is sneakier. Of course avoidance is the best strategy; but in case that fails, it’s important to recognize what problem you’ve got and know how to treat it.
1) McIntosh, Scott E. et al. (2011) Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Frostbite. Wilderness & Environmental Medicine , Volume 22 , Issue 2 , 156 – 166. http://www.wemjournal.org/article/S1080-6032(11)00077-9/fulltext
2) Ken Zafren et al. 2014. Wilderness Medical Society Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia. Volume 25, Issue 4, Pages 425–445, DOI: http://dx.doi.org/10.1016/j.wem.2014.09.002