In most adults, an oral
temperature above 100.4 °F (38 °C) or a rectal or ear temperature above
101 °F (38.3 °C) is considered a
fever. A child has a fever when his or her rectal temperature is
100.4 °F (38 °C) or
What can cause a fever?
A fever may occur as a
- Infection. This is the most common cause of a
fever. Infections may affect the whole body or a specific body part (localized
- Medicines, such as
antihistamines, and many others. These are called drug
fevers. Some medicines, such as antibiotics, raise the body temperature
directly. Other medicines interfere with the body's ability to readjust its temperature
when other factors cause the temperature to rise.
- Severe trauma or
injury, such as a
heat exhaustion or
heatstroke, or burns.
- Other medical
conditions, such as arthritis,
hyperthyroidism, and even some cancers, such as
Hodgkin's lymphoma, and liver and
Can a low body temperature be dangerous?
abnormally low body temperature (hypothermia) can be serious, even
life-threatening. Low body temperature may occur from cold exposure,
shock, alcohol or drug use, or certain metabolic
disorders, such as
hypothyroidism. A low body temperature may also be
present with an infection, particularly in newborns, older adults, or people
who are frail. An overwhelming infection, such as
sepsis, may also cause an abnormally low body
Can a high body temperature be dangerous?
Heatstroke occurs when the body fails to regulate its own temperature and body
temperature continues to rise. Symptoms of heatstroke include mental changes
(such as confusion, delirium, or unconsciousness) and skin that is red, hot,
and dry, even under the armpits.
Classic heatstroke can develop
without exertion when a person is exposed to a hot environment and the body is
unable to cool itself effectively. In this type of heatstroke, the body's
ability to sweat and transfer the heat to the environment is reduced. A person
with heatstroke may stop sweating. Classic heatstroke may develop over several
days. Babies, older adults, and people who have chronic health problems have the
greatest risk of this type of heatstroke.
may develop when a person is working or exercising in a hot environment. A
person with heatstroke from exertion may sweat profusely, but the body still
produces more heat than it can lose. This causes the body's temperature to rise
to high levels.
Both types of heatstroke cause severe dehydration
and can cause body organs to stop functioning. Heatstroke is a life-threatening medical emergency requiring emergency medical