Appliance of Science: Why do we feel cold when we have a fever?

This question was sent in by a reader from Dublin. We all know what, it’s like, the thermometer says our temperature is up but all we want to do is wrap ourselves in blankets and sit near a warm fire. So why is that? 

Firstly, we need to take a look at what our normal body temperature is and how it is regulated.

BODY TEMPERATURE AND REGULATION

Our body temperature is usually between 36.1 and 37.2C. This varies depending on age, health, how the temperature is taken and a variety of other factors.

HOW DOES OUR BODY CONTROL AND MAINTAIN THESE TEMPERATURES?

It uses a thermostat. Our internal thermostat is located in a part of our brain, called the hypothalamus. It is set at 36.8C.If our body temperature goes above this we do certain things to cool down; if our temperature drops, we need to warm up.

COOLING DOWN

The body uses two main systems to cool down. One is that it sweats; body heat transfers to the sweat (or any water on the body) and the heat is removed from the body when the sweat is wiped away or evaporates. This also explains why we feel cold coming out of a swimming pool, even on a very hot day. The flow of blood to vessels that sit just below the skin also increases. This brings heat to the surface of the body to be released. This explains why we often have a red face when we are hot.

HEATING UP

If our body temperature drops below that set on our internal thermostat then we need to heat up. This time we reduce the blood flow to capillaries near the body’s surface, to reduce the amount of heat lost through our skin. We also get certain muscles moving to burn some energy and heat up the body.

USING HEAT AS A WEAPON

Often, when our body is attacked by a microorganism, like a virus or bacteria, it responds by altering the temperature of our body.

Most viruses and bacteria grow best in warm temperatures; 37C is ideal for many microorganisms. Unfortunately this is around the normal temperature of the human body. So what does the body do to try to stop these infecting organisms from growing, reproducing and taking over? It turns up the thermostat. So the fever we experience is created deliberately, to try to suppress an infection.

WHY DO WE SHIVER?

When the thermostat is turned up, our normal body temperature is lower than the new setting and we feel cold. The body kicks into action, bringing the temperature up. To do this it gets certain muscles to start to contract involuntarily. This burns up energy within the body, giving off heat and increasing the body’s temperature. The involuntary muscle contractions are what we call shivering. Usually the increase in temperature is enough to stop the infection from spreading within the body. Once our immune system kills of the infection and our body is safe, then the thermostat is reset to 36.8C and out body temperature drops back down to normal again.

Naomi is a science communicator and mother to three inquisitive children. She can be found at sciencewows.ie

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