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What Is Hypothermia?

How Does Cold Exposure Cause Hypothermia?

During exposure to cold temperatures, most heat loss -- up to 90% -- escapes through your skin; the rest, you exhale from your lungs. Heat loss through the skin happens primarily through radiation and speeds up when skin is exposed to wind or moisture. If cold exposure is due to being immersed in cold water, heat loss can occur 25 times faster than it would if exposed to the same air temperature.

The hypothalamus, the brain's temperature-control center, works to raise body temperature by triggering processes that heat and cool the body. During cold temperature exposure, shivering is a protective response to produce heat through muscle activity. In another heat-preserving response -- called vasoconstriction -- blood vessels temporarily narrow.

Normally, the activity of the heart and liver produce most of your body heat. But as core body temperature cools, these organs produce less heat, in essence causing a protective "shut down" to preserve heat and protect the brain. Low body temperature can slow brain activity, breathing, and heart rate.

Confusion and fatigue can set in, hampering a person's ability to understand what's happening and make intelligent choices to get to safety.

What Are the Risk Factors for Hypothermia?

People at increased risk for hypothermia include:

  • The elderly, infants, and children without adequate heating, clothing, or food
  • People with mental illness
  • People who are outdoors for extended periods
  • People in cold weather whose judgment is impaired by alcohol or drugs

What Are the Symptoms of Hypothermia?

Hypothermia symptoms for adults include:

  • Shivering, which may stop as hypothermia progresses (shivering is actually a good sign that a person's heat regulation systems are still active. )
  • Slow, shallow breathing
  • Confusion and memory loss
  • Drowsiness or exhaustion
  • Slurred or mumbled speech
  • Loss of coordination, fumbling hands, stumbling steps
  • A slow, weak pulse
  • In severe hypothermia, a person may be unconscious without obvious signs of breathing or a pulse

Hypothermia symptoms for infants include:

  • Cold-to-touch, bright red skin
  • Unusually low energy

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