Think Out Loud

How our bodies react to cold

By Rolando Hernandez (OPB)
Jan. 7, 2022 5:44 p.m. Updated: Jan. 10, 2022 9:32 p.m.

Broadcast: Monday, Jan. 10

Multnomah County had one death linked to hypothermia last month.

Multnomah County had one death linked to hypothermia last month.

Emily Cureton Cook / OPB


Within the past month, Multnomah and Jackson County have seen deaths related to hypothermia. What happens when our body can’t handle the cold? What does this mean for people in the homeless community who can’t make it to warming spaces? Matt Hansen, associate professor of emergency medicine and pediatrics at OHSU, joins us to answer these questions.

The following transcript was created by a computer and edited by a volunteer.

Dave Miller: This is Think Out Loud on OPB, I’m Dave Miller. Winter storms and cold in Oregon over the last few weeks didn’t just close roads and boost the region’s snowpack. They also took lives. Multnomah and Jackson Counties reported deaths connected to hypothermia. We wanted to know more about hypothermia, so we called up Matt Hansen. He’s a professor of emergency medicine and pediatrics at OHSU. We talked last week. I asked him if he could explain what happens when people are exposed to cold.

Matt Hansen: Sure. The first thing that happens when you’re in a cold environment and your body is exposed to that cold temperature is your body will try to preserve its heat by sending the blood away from the extremities, from the arms and legs, and shunting it to your core to keep your vital organs warm. And that happens by narrowing the blood vessels, sort of focusing the blood flow towards your core to preserve warmth. So your arms and legs tend to get cold first. And then if the core temperature actually starts dropping, then gradually, the body’s functions and vital functions stop working like they normally do. Your body is calibrated to function at a pretty specific and narrow range of temperatures. All of us know, it’s around 98.6 is normal temperature. And if you get more than a few degrees away from that in either direction, the signaling that happens, the enzymes, the proteins, they don’t work like they’re intended to. And so you start seeing vital functions of the body become disrupted.

With cold temperatures, the first major thing that gets disrupted when your core temperature starts dropping is brain function decreases, and people will become confused. They’ll potentially hallucinate, and they won’t do things that will naturally bring them back into a warm environment. So you notice, the first thing that you would do if you get cold is you’re going to try to put on an extra jacket or go inside or get out of the wind. But once your core temperature has dropped, those natural instincts won’t kick in anymore. You’ve probably heard of stories of mountain climbers that are found with their gloves and their coats off when they died from hypothermia because there’s confusion and brain brain dysfunction that happens.

Miller: Is it fair to say that people are pretty far gone at that point, if they get to the point where they’re taking off their clothes because they feel hot, that’s an extreme warning sign?

Hansen: Definitely. I think a really important warning sign, or you might say extreme warning sign, is confusion, in the setting of low body temperature. If you’re out there in the community trying to help someone who might be really cold, if they seem confused, that’s a really strong indication that they need medical attention for it, and not just to be warmed back up in a building or somewhere else.

Miller: You know, that’s an important point, because I can imagine somebody mistaking that kind of mental confusion, ascribing it to other reasons, say alcohol use or drug use or mental health issues. But you’re saying the cold itself could be one of the reasons or the reason for that mental confusion.

Hansen: Yes, exactly. And your temperature has to get below about 32°C, which is around 90°F, in order for you to get to that level. And so, when you’re confused because of the cold, you’ve lost a lot of body heat already, and that’s where the other bodily functions can also be at risk of shutting down.

Miller: At what point is going inside and getting warmer not enough? At what point does someone need medical help?


Hansen: That’s a great question. I think for the layperson, it can be very very difficult to judge. There are some things that can reassure you that you don’t need medical attention. Usually if someone is still shivering, then that usually means that they are above that threshold where they would need medical attention. Intact shivering is a good sign that your temperature is a little low, but not dangerously low.

Miller: And your body still has the ability to move itself in a way that could create enough warmth to be safe again. That’s what the shivering is?

Hansen: Yeah, the shivering is your body is moving rapidly, muscle contractions are happening, that will generate heat, trying to rewarm yourself. People in that situation can certainly be brought indoors out of the rain, out of the cold, and re-warm safely, without medical attention.

Miller: But at a certain point, you’re saying a body stops doing and that’s a serious warning sign?

Hansen: Correct. So if you get to the point where you’re no longer shivering, that’s getting closer to the point where it’s more serious. And when you reach that stage where someone is confused because of the cold, which as you mentioned can be very challenging because of potential intoxicants or other issues, then it’s time to seek medical attention. And I think when we’re in the middle of a really cold snap, we need to err on the side of caution for bringing people to get medical attention if they could be that low. Oddly enough, we don’t see a lot of really severe hypothermia in our hospitals in Portland. They tend to be concentrated during the really cold times, when the temperature drops quite a bit below freezing is when we see more of them.

Miller: In prepping for this conversation, I was struck by a finding I saw that came from a big survey from the Lancet, the British medical journal. They looked at something like 75 million deaths from a number of different countries over the course of a few decades. And their finding was that cold kills 20 times more people than heat does, which is counterintuitive, given the way I think popularly, a lot of us hear about or think about the dangers of heat stroke or heat exhaustion, and the dangers of cold. How do you explain that? It’s a gigantic gulf between the effects of cold in terms of global populations and the effects of heat.

Hansen: That’s a good question. I’m not familiar with that study, and having not read it, it’s hard to comment. But some factors could be where human populations are concentrated. I guess there are people that live in hot and cold areas. It might be that getting out of the heat is easier than getting out of the cold. In the heat, often just getting into the shade and then getting some liquids is a huge reprieve. But in the cold, you actually need basically artificial warmth. You need some sort of heat source, some sort of fuel source or something to allow yourself to be rewarmed. And so it might just be that it’s easier to get relief from the heat than it is from the cold. But I’m not sure. That’s a good question.

Miller: What are the challenges, from a medical perspective, when someone does come to an emergency department suffering from severe hypothermia? How do you safely warm them up again?

Hansen: So there are several stages of hypothermia, and the stage of hypothermia dictates how we warm them. When you’re in the mild stage of hypothermia, which is when your core temperature is greater than 32°C or about 90°F, then just being in a warm environment with warm clothing, oral drinking fluids is enough. But once you get between 28°-32° C, which is roughly in the 82°-90°F range, then we use active rewarming. We have forced air heated blankets or chemical heating packs, warmed IV fluids, and things like that, more aggressive warming. We warm the entire body, the core and the limbs, at the same time. And then once folks are below about 82° degrees or 28° degrees Celsius, then sometimes we use very invasive rewarming techniques, including heart-lung bypass machines that can actively rewarm the blood outside the body and then put it back in.

Based on how cold the temperature is, we use more advanced techniques, and sometimes very invasive techniques. Once your temperature gets below 32°C and especially below 28°C, you’re at risk for a complete cardiac arrest, from either the heart just completely stopping or going into an abnormal rhythm, and we can’t necessarily fix that until the body has been rewarmed. So we get pretty aggressive with those.

Miller: Portland and the Portland area, most of the Willamette Valley, has a relatively temperate climate, especially compared to places in the US like the Upper Midwest or parts of the Northeast. But how cold does it need to be to be dangerous if you are outside and unsheltered?

Hansen: That’s a good question. I’ll harken back to what I said before. We don’t see, in our normal weather, the weather that we’re having this week for example where the temperatures are in the 40s and 50s, we don’t tend to see a lot of people suffering from hypothermia. It’s quite unusual. We do see a lot of people with wet feet that have immersion, foot-related issues. That’s very common in these wet months, where the temperature is not super cold. Theoretically, you can become dangerously hypothermic when the temperature is in the 40s and 50s, if you’re wet, if you don’t have enough clothing on, and if you’re really exposed to the elements. People in our community have adapted to shelter and clothe themselves in such a way that they are able to tolerate the environment that we have with these 40s and 50s type temperatures. And then when we run into trouble is when it drops below freezing, especially quite a bit below freezing.

Miller: What are the foot related issues that you’re talking about? I think you said immersion related issues. If people’s feet are wet for long periods and cold, what do you see in the emergency department?

Hansen: We see that very commonly. People will call it immersion foot. It’s basically having wet feet for an extended period of time. It causes damage to the skin. It can cause fungal infections. It can cause a lot of blistering skin breakdown and wounds on the feet. It can become very painful. It’s not usually life threatening, but it can be quite disabling. And we see that very frequently during the wintertime in our population of people experiencing homelessness, and so efforts to get people dry socks are really important. It’s really easy to get your feet wet with puddles and rain, and really hard to get them dry.

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