While it is important to keep our bodies properly warm, it is equally important for us to be able to cool down. But in certain environmental conditions our bodies cool down too much. Our temperatures drop too far when they dip into hypothermic internal temperatures of 95 degrees and lower.
There are four main ways that our bodies give off heat and cool themselves: conduction, convection, radiation and evaporation. Each of these processes helps us sustain healthy internal temperatures. They also give us a better understanding of how hypothermia happens.
We constantly release heat in the form of radiation. In the same way the sun emits heat down on us as we bask on a beach, our bodies exude heat as a natural by-product of our metabolism.
When you hold a chocolate chip in your hand for a few minutes, it will likely begin to melt. This process is called conduction. It occurs when our bodies come into contact with something that has a lower temperature. The body gives away heat to that other object.
If we give away heat to something in motion, however, convection takes place. When wind puts air particles in motion, they take away heat as they hit our bodies and move away. That's why a wind chill can make it feel colder outside than the true temperature.
Our blood vessels also play an integral role in heating and cooling. They expand or constrict to free or restrict blood flow to our skin tissue. When our metabolism heats up our insides, it warms our blood as well. To control that building heat, blood vessels at our skin dilate -- like our pupils in low light -- to circulate more of that warmed blood toward the skin's surface and allow the body to release heat. This opening of the blood vessels is called vasodilatation. Alcohol and tobacco both cause vasodilatation, which is why both substances can give you the sensation of warmth, even though your core temperature is colder.
Since our bodies naturally give away heat to colder, active particles, air particles in wind and water particles can accelerate that effect. Water is denser than air, so it absorbs more heat. That's why water can steal up to 32 times more heat from our bodies than air can [source: U.S. Search & Rescue Task Force]. Even when we get caught in a rain shower, it can lead to hypothermia because of how quickly water cools us.
To combat this rapid cooling, we shiver. Think about being outside on a winter day and how, as the cold hits, you instinctively bring in your arms and legs and tighten those muscles. Shivering is our bodies' way of generating heat by exciting our muscles. Our blood vessels also constrict to limit the amount of blood travelling toward our skin.
When someone's re-warming reactions, like shivering, aren't enough to overcome the cooling process, hypothermia can set in. Look for several important signs indicating the different stages of hypothermia.
- Mild Hypothermia: shivering, goose bumps, difficulty with complex motor skills
- Moderate Hypothermia: violent shivering, sluggish, speech problems, difficulty with fine motor skills
- Severe Hypothermia: rigid muscles, dazed, shivering has stopped, blue skin, erratic heart beat, unconscious
If severe hypothermia sets in, complications can include coma and even death. Other cold weather injuries are also associated with hypothermia, such as frostbite, chilblains (ulcers on the toes) and trench foot (a foot infection). For more information on protecting yourself from the cold, read How to Survive the Freezing Cold.
Now that we understand how our bodies can cool too rapidly and cause hypothermia, we'll learn ways to prevent that from happening.