[Karl Avillo]

Karl Avillo  asked the Naked Scientists:
   
Why is it that we shiver when we have a very high fever and when it's very cold? thank you.

I'm from the Philippines and I download all your podcasts.

They are all great indeed!

What do you think?

[CliffordK]

A fever is part of your body's immune response to an infection.  Perhaps combating the infection with an unfavorable body temperature for the microbe, perhaps part of increased activity in the body.  Essentially it is a change in your body's temperature set-point.

Generally it is not recommended to physically cool the body unless you have an extreme temperature, perhaps greater than about 105°F (40.5°C) that isn't responsive to ordinary antipyretic drugs, in which case you certainly should be consulting a physician.

For "ordinary" fevers, you should try to get comfortable.  If you feel cold, put on extra blankets.  If you feel hot, take off some blankets. 

The shivering is a sign that your body thinks it should be warmer by initiating muscle movements to generate heat.

Sweating would be a sign that your body thinks it should be cooler.

[CZARCAR]

evolved thru time. Higher temp helps fight invading microorganism, shivering prompts using blanket to induce even higher temp.

[freecw]

When your immunue cells kills the invading pathogen they release pyrogens which result in an increase of your body's set temperature past 98.5. Once this happens your body feels that it is cold and needs to increase its temperature, so it induces merchanisms to increase body temeprature such as shivering and posture changes. Your body usually overshoots the temperature so it stops for a while to cool down, then it cools down too much and you start shivering again, which is why when you have a fever you have these drastice changes in body temeprature till you reach the new setpoint.
The increased temeprature increases rate of enzymes which means white blood cells become more efficient. Also, most pathogens have a set point in which they can survive. Changing your body temperature by even a few degrees can kill off some of the pathogen that may be causing the infection.