Fever is an elevated temperature of the human body that is
substantially beyond the normal range. Normal body temperature
fluctuates daily from about one degree below 98.6 degrees Fahrenheit to
one degree above that number. Lower body temperatures usually occur
before dawn; higher temperatures in the afternoon.
Body temperature also varies slightly depending on where on the
human body it is measured. Rectal (internal) temperature tends normally
to be higher than skin (surface) temperature. Oral and armpit
temperatures can approximate actual body temperature and are more
convenient to measure.
The presence of a fever is usually related to stimulation of the
body's immune response. Fever can support the immune system's attempt to
gain advantage over infectious agents, such as viruses and bacteria,
and it makes the body less favorable as a host for replicating viruses
and bacteria, which are temperature sensitive. Infectious agents are not
the only causes of fever, however. Amphetamine abuse and alcohol
withdrawal can both elicit high temperatures, for example. And
environmental fevers--such as those associated with heat stroke and
related illnesses--can also occur.
The hypothalamus, which sits at the base of the brain, acts as
the body's thermostat. It is triggered by floating biochemical
substances called pyrogens, which flow from sites where the immune
system has identified potential trouble to the hypothalamus via the
bloodstream. Some pyrogens are produced by body tissue; many pathogens
also produce pyrogens. When the hypothalamus detects them, it tells the
body to generate and retain more heat, thus producing a fever. Children
typically get higher and quicker fevers, reflecting the effects of the
pyrogens upon an inexperienced immune system.
Should one eat little or nothing while feverish, as the saying
"Feed a cold, starve a fever" suggests? Yes. The reasons for this are
threefold. First, during fever, all the body's functions are occurring
amidst increased physiologic stress. Provoking digestion during
physiologic stress over stimulates the parasympathetic nervous system
when the sympathetic nervous system is already active. Second, it is
possible that the body could misinterpret some substances absorbed from
the gut as allergens during a fever. Finally, excessive fever can, on
rare occasions, cause seizures, collapse and delirium--all of which may
be further complicated by recent eating.
Fever can help fight infection, but sometimes it can climb too
high for the body's own good. Internal body temperatures in excess of
105 degrees F, for instance, expose proteins and body fats to direct
temperature stressors. This form of heat distress can threaten the
integrity and function of proteins accustomed to the body's usual
temperature variations and the occasional less excessive fevers.
Cellular stress, infarctions, necrosis, seizures and delirium are among
the potential consequences of prolonged, severe fevers. The receptor
environment at the hypothalamus maintains limitations on high fevers. In
the rare instances in which the hypothalamus itself malfunctions, the
result is typically low body temperature, not elevated body temperature.
