What part of the body loses the most heat in cold water
Due to a higher blood flow in the head and neck than in the rest of the body, 40 to 45 percent of body heat is lost through the head and neck.

The body constantly generates and radiates heat to its surroundings. The body loses most of its heat when submerged in cold water from the head, neck, sides of the chest (both ribcage and armpits), and groin.

Due to higher blood flow in the head and neck than in the rest of the body, 40 to 45 percent of body heat is lost through the head and neck. The majority of body heat is produced by deep organs, including the brain, liver, heart, and by skeletal muscle contraction.

How can you reduce heat loss when in cold water?

You are recommended to keep your body in the heat escape lessening position (HELP) or huddle position when submerged in water.

  • HELP position: Your knees are drawn up to your chest, your upper arms are at your sides, and your lower arms are folded on your chest.
  • Huddle position: This is done when two or more people are together in the water. Put your arms around each other's shoulders so that your chests are touching.

These are floating positions in cold water that are easier to perform while wearing a life jacket. If you are in proximity to land, you are recommended to swim toward land as soon as possible.

How does the body lose heat?

Your body loses heat in four ways that include:

  1. Radiation: Radiation is the movement of energy in the form of electromagnetic waves. The sun and bonfire are classic examples of radiation.
    • You may feel the heat emitting from the source whether you stand in the sun or next to the campfire. Because your body works in the same way, radiation is typically the primary source of heat loss.
    • Even in a normal atmosphere, such as 70°F, you will lose about 60 percent of your body heat through radiation. This form of heat loss is difficult to prevent.
  2. Conduction: Conduction is the direct transport of heat away from your body through objects with which it comes into contact.
    • Air is a poor heat conductor, whereas water is not. Water transfers heat far more effectively than air, up to 25 times more or so.
    • When you swim, water immediately absorbs your heat. However, you don't even have to be in the water for this to happen. You may be kayaking along a freezing river or lake, and if you aren't properly clothed, you will feel a fast chill go through your body.
  3. Convection: Convection occurs when colder water or air comes into touch with your body. The media that comes in contact with the body gets warm and moves away. 
    • The warm water or air that moved along with the heat is replaced with cooler water or air that comes in contact with the body. As this cooler media gets warmed, heat loss increases, and the process continues.
    • Convective heat loss is the greatest in a flowing body of water, such as a river. Assume you go swimming in a strong current. The water absorbs more heat from you than the air, and it sweeps away any warm water from around you.
    • Even air efficiently draws heat away. This is where wind chill originates from and why you might feel considerably colder than the actual temperature.
  4. Evaporation: Evaporation is the process through which liquid water converts to water vapor. This necessitates the use of heat.
    • When you breathe out in the cold, you bring cold air from your surroundings into your lungs. As you do this, your body heats the air, and as you exhale, you expel warm air.
    • Compared with other methods of heat loss, this is the smallest, but you may limit it by simply covering your face to warm-up part of the air you breathe in before drawing it into your lungs.

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What is hypothermia?

When your body is exposed to cold conditions, it begins to lose heat quicker than it can create it. Long-term exposure to cold will deplete your body's stored energy and slow down cell functions. As a result, hypothermia, or unusually low body temperature, occurs.

A low body temperature affects the brain, causing the person to be unable to think effectively or move well. This makes hypothermia particularly hazardous because the person may be unaware that it is occurring and unable to intervene.

Hypothermia is more common in extremely low temperatures although it can occur even in warm weather, which is over 40°F if a person becomes chilled after being wet due to rain or perspiration or immersion in cold water.

The most common victims of hypothermia include:

  • Elderly individuals with insufficient food, clothes, or heating
  • Newborns sleeping in chilly beds
  • People who spend an extended amount of time outdoors such as the homeless, hikers, or hunters
  • Intake of alcohol or use of illegal substances

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Medically Reviewed on 4/6/2022
References
Image Source: iStock Images

Where Does Most Of Your Body Heat Escape: https://bikehike.org/where-does-most-of-your-body-heat-escape/

Hypothermia: Understanding and Prevention: https://seagrant.umn.edu/programs/recreation-and-water-safety-program/hypothermia