Why do we feel both hot and cold when we’re sick?

Cecil replies:

Dear Shannon:

This is a little complicated, but if I can explain Social Security, I can explain this. Under normal circumstances your core body temperature is maintained at a constant level by a glandular control center called the hypothalamic thermostat. During a fever, bacteria and degenerating body tissue give off substances known as pyrogens, which somehow cause the hypothalamic thermostat to ratchet up a notch. A host of physiological mechanisms then kicks in to elevate the body’s temperature, which usually takes several hours. At the outset the body is way colder than the hypothalamus wants it to be, so although you’re heating up, you feel cold, experiencing shivering, goose bumps, vasoconstriction of the skin (clamminess), etc. By and by you reach fever temperature, and the chills stop. When the fever breaks the hypothalamic thermostat drops back to normal. You perspire, and because of vasodilation (enlarging of the surface blood vessels, allowing more blood to flow) your skin becomes flushed and hot, even though objectively you’re cooling off. Sound a little complicated? All I can tell you is, don’t sweat it.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.