While one might think freezing to death would be just that — slowly freezing up and doing little else — humans actually do some pretty weird things before they meet an icy end. Here’s what happens when we face a serious cold, and what our bodies do to try and save us.

Baby, It’s Cold Outside

Cold weather is usually no more than an annoyance, but if a person is caught without proper clothing, or facing exposure for an extended period of time, extreme cold becomes more than just a reason to cancel school. There is no set temperature when danger sets in, since there are many factors that affect how quickly a person develops hypothermia. For example, older people have been known to develop hypothermia in conditions that would be fine for a younger person, and those with alcohol in their system are more vulnerable to cold than their sober counterparts (apologies to those who believe in the “alcohol coat”). In general, being exposed to freezing temperatures or falling into freezing water puts everyone at risk for low body temperature.

Defined as a core body temperature of 95 degrees F or lower, hypothermia causes the heart, nervous system, and other organs in the body to have trouble working correctly. Without treatment, the condition can lead to some pretty dark places, including respiratory failure and death.

“The heart and liver produce much of the body’s heat, in coordination with the brain’s temperature center, the hypothalamus,” Dr. Joe Alton, author of The Survival Medicine Handbook, told Medical Daily in an email. “As core body temperature cools, these organs produce less heat.”

When our temperature begins to drop, we start to shiver. Though we may not appreciate the teeth chattering, shivers are actually a reflex triggered to keep us warm: a rapid tightening and loosening of body muscles meant to produce heat. Our body also initiates something called vasoconstriction, a tightening of blood vessels in the extremities, to redirect blood to the deeper, more important tissues. This helps the body reduce the amount of heat lost to the outside environment and is why alcohol, which expands blood vessels, makes us more vulnerable to hypothermia.

Along with these defenses, mild hypothermia symptoms include dizziness, faster breathing, and a weakened pulse. A dangerously low body temperature doesn’t only have physiological effects, though, and it starts messing with our brains as things get more serious.

A remote, mountainous landscape like this is where many explorers have fallen victim to hypothermia. Shaylor (CC BY-ND 2.0)

On Thin Ice

Once core body temperature reaches about 91 degrees F, respiration and heart rate begin to slow to dangerous levels. This will eventually lead to a loss of consciousness, but before that happens, those suffering from hypothermia feel confused, think and speak sluggishly, and some experience anterograde amnesia. A loss of reasoning is also a key symptom of severe hypothermia, and one that can lead to problematic behaviors.

Over time in the cold, the muscles responsible for keeping our blood vessels constricted become exhausted and fail, meaning all of the warm blood that had been pulled from the extremities suddenly rushes back to them. This causes what can only be described as a hot flash, making a person suffering from severe hypothermia feel as if they’re burning up for a moment. Though this is truly an insidious sign, a person whose brain has already been muddled by hypothermia takes it only at face value — they feel hot, so they begin to remove all of their clothing. Referred to as paradoxical undressing, this bizarre behavior was found to have occurred in 25 percent of fatal hypothermia cases in one study.

As if getting naked wasn’t a weird enough reaction, the brain has one last-ditch effort in store to try and save us from freezing. Described by researchers as a primitive instinct borne of the brain stem, terminal burrowing is a behavior seen in both hibernating animals and humans suffering from severe hypothermia. Terminal burrowing behavior refers to the instinctual impulse to reach a safe place, to dig into snow or huddle oneself under something in a position that indicates a “final mechanism of protection.”

Paradoxical undressing and terminal burrowing often go hand-in-hand, and they are often followed swiftly by death. At a core body temperature between 85 and 71 degrees F, an inability to move and a low blood pressure lead to coma. Below 71 degrees, muscles grow rigid, and the heart and breathing rate continue to decrease until the person reaches death.

Though the general limit for human survival falls somewhere above this temperature, there have been some incredible cases of recovery that defy this limit. The most notable example is that of a female skier who, after falling into icy water and remaining submerged for 40 minutes (with only a small air pocket beneath the ice to breathe from), survived her ordeal. When rescuers arrived, she had no pulse, and no circulation. Doctors worked on the woman for nine hours just to get her vital signs back, and she had to spend two months in intensive care to regain the use of her organs and limbs. She made a mostly full recovery, though, after her body temperature had dropped to an astonishing 56.7 degrees F, the lowest survived body temperature ever recorded.

So if you’re planning on braving the cold this winter, layer up, toughen up, and stay safe — because not all of us can pull off record-breaking body temperatures. Take a look at the video below for a representation of prolonged exposure can cause hypothermia.