A drop in body temperature below 95 degrees. A severe case would be 86 degrees or lower. When core temperature drops, the brain’s hypothalamus (our built-in thermostat) triggers several reactions:

Mild cases
Severe cases
Drowsiness, confusion, loss of coordination, loss of consciousness
Blood vessels in skin and extremities constrict to concentrate warm blood around the core
To preserve skin tissue, blood vessels periodically dilate at the surface, giving us rosy cheeks
Slurred speech
Muscles shiver to produce heat
Heart rate drops, breathing becomes shallow
Goose bumps raise hairs to trap air for insulation — great for furry mammals but useless to us

What you can do

  • Replace wet clothes with warm, dry clothes and blankets.
  • Get out of the wind.
  • Drink warm beverages without caffeine or alcohol.
  • Be careful with electric blankets and hot packs — they can burn.
  • Call 911 if a person is unconscious.

Frostbite (or its little brother, frostnip)

Damage to skin and other tissues from freezing. Face, ears, fingers and toes are most vulnerable. Because less blood is flowing to the skin and extremities, they can freeze faster.


Ice crystals form in and around cells, which causes damage and clotting. Nerve impulses and muscles slow.

  • Pain, itching, numbness
  • Skin turns white, gray or yellow
  • Fingers lose dexterity


Blood can’t reach oxygen-starved tissue, and cells begin to die. If muscles, tendons and nerves freeze, amputation may be required.

  • Skin feels hard, stiff or waxy
  • Purple or black blisters may appear
  • Gangrene can't set in

What you can do

  • Replace wet clothes with warm, dry clothes and blankets.
  • Warming should be gradual, with warm (not hot) water until color returns.
  • Don't rub — that can cause more damage.
  • If a person has severe frostbite, get immediate medical attention.

Who is at risk?

Anyone can suffer from overexposure to cold, but some groups are more susceptible.

The young and the old

Weak bodies can’t fight off cold as well as healthy ones. Diabetics may not feel the onset of frostbite. Cold air can trigger asthma attacks and other respiratory problems.


Alcohol dilates blood vessels at the skin surface, allowing more heat than usual to escape. It also contributes to dehydration, which can occur faster in cold, dry air.

People who work or exercise outside

Wind and moisture, even from sweat, accelerate heat loss. Hikers, skiers and anyone who spends a lot of time outside should carefully dress in layers and cover as much skin as possible.

SOURCES: U.S. National Library of Medicine, Baylor University Medical Center, Centers for Disease Control and Prevention, Medical News Today, WebMD.