Why Do We Feel Chills When We Get Sick?

I got sick a few days ago. Some kind of pulmonary infection that started with chest pain and within 12 hours has made me powerless, snotty and coughing man. And, of course I was not able to avoid the paradoxical feeling of chills… agree it's a bit strange to feel the cold when your temperature is +39 °C.

I never thought about this process in details before. I was satisfied with the guess based on physics:

The temperature of my body increases sharply in comparison with the ambient temperature, and therefore it seems to me that it gets cold…

But my body is much smarter than my brain!

Evolution has allowed our cells to form a response to any process, which is a threat to the health and survival of each of these cells and the organism as a whole. One of the most dangerous and common threats is an internal infection- Infection of living organisms by the foreign microorganisms (bacteria, viruses, fungi).

image source

Our brain (much earlier than all scientists of the earth) discovered that the majority of protozoa, bacteria and viruses die when the temperature rises. A temperature +38°C stops the reproduction of most kind of viruses, 38.5°C-39°C starts to kill them.

In a sense, the hypothalamus is a smart thermostat of our body. It processes information about temperature of the organism and the presence of infection.

If it becomes apparent that temperature 37-38°C is not enough to fight off the infection, then get ready for the chills.

The hypothalamus increases the maximum temperature value for the entire body, to effectively fight infection. Then the brain starts two interesting reactions:

• Comes a spasm of the superficial vessels and muscles, goosebumps appears. It reduces the heat output to the external environment.
  

  
  The arrector pili muscles are raising the hairs (image source)

• Almost at the same moment comes the contraction of the muscles throughout the body from the top down: muscles of mastication, muscles of the shoulder girdle, muscles of the back and limbs. The contraction of muscles leads to a sharp rise in temperature inside the body, goosebumps keeps the heat inside.

Chills is some kind of Turbo-Mode to changing the temperature. Just a couple of hours, your temperature may increase by 1.5-2°C or even 3°C, it is fatal to many foreign microorganisms.

But at such high temperatures also begin to die healthy cells. Millions of dead cells and viruses cause intoxication (poisoning) of the whole organism, that's why we feel aching joints.

Temperature and its duration depends on the severity of the infection. With a mild cold, it will be enough to fry the viruses at +37°C a day or two. With more serious diseases (such as influenza), the hypothalamus forced to constantly increase the allowable threshold temperature (up to +41°C).

With its simplicity and automation, this process once again shows that the nature is amazing. Any organism on our planet has the skills of protection and attack at the genetic level. Of course it is not an individual reaction to any type of infection, but rather the basic rules. Nevertheless, they help us cope with the majority of potentially deadly viruses.

In conclusion, I would like to wish you all be healthy! ;)