Body temperature is measure of the body's ability to produce and get rid of heat. The temperature of the body can be measured in several locations on the body, most commonly the mouth, armpit, ear, and rectum. Thermometers are used to measure the body temperature and can be calibrated in degrees Fahrenheit (°F) or degrees Celsius (°C) depending on the global region.
The "normal" body temperature of 98.6°F (37°C) is actually an average of temperatures. A person's "normal" temperature can fluctuate 1°F (0.6°C) or more or below 98.6; additionally, the body temperature fluctuates the same amount throughout the day - lower in the morning and evening while higher at mid-day. Hormone levels can also affect body temperature, particularly in women who are ovulating or menstruating. The location at which the temperature is taken has an affect on the temperature reading. Rectal or ear temperature readings tend to be as much as 1°F higher than an oral reading; armpit readings are generally 1°F lower than oral readings.
A spike in body temperature is called a fever. In most adults, an oral temperature in excess of 100°F (or rectal/ear temperature over 101°F) is considered a fever. A fever in a child occurs when his or her rectal temperature exceeds 100.4°F. Fevers can be triggered by numerous situations ranging from infections (most common cause); severe trauma or injury such as stroke, heart attack, or burns; certain medicines like barbiturates, antihistamines, and narcotics (called drug fevers); other medical conditions, such as hyperthyroidism and arthritis; and even certain cancers - liver cancer, lung cancer, and leukemia. If a fever reaches or exceeds 104°F, see a health professional immediately.
When treating a minor fever at home, wear light clothing and use light blankets or similar bedding. Drinking cool liquids will help to lower the body's temperature. A bath or shower with lukewarm water can assist in lowering the temperature, but do not use cool or cold water; this will cause shivering and contraction of the blood vessels near the skin, raising the temperature further. Fever-reducing medications such as acetaminophen (such as Tylenol) and ibuprofen (Advil or Motrin) can also lower the temperature. Aspirin is not recommended for anyone under the age of 20 due to the risk of a rare condition called Reye's syndrome, which primarily affects children 6 to 12 years of age. Do not administer aspirin to children who have recently had chickenpox (varicella) or influenza, as this increases the risk of developing the syndrome.
On the other end of the spectrum from a fever is hypothermia, when the body temperature falls below 97°F. Shock, prolonged exposure to cold, alcohol/drug use, and some metabolic disorders (such as diabetes mellitus) can cause hypothermia. A low body temperature, just like a high one, can be caused by an infection; this occurs primarily in newborn babies, the elderly, and people who are frail.
Taking one's temperature within an hour of exercise or taking a bath/shower will lead to an inaccurate temperature reading. Taking an oral temperature within 20 minutes of smoking or drinking any liquid will also produce an inaccurate reading.
Note: Glass thermometers containing mercury are no longer recommended for use. If you have a glass thermometer, please contact your local health department for disposal instructions.
Fluctuating temperatures throughout the day of more than 2 degrees indicates poor adrenal function.
Consistent low temperature throughout the day of more than 2 degrees lower than 98.6 indicates poor thyroid function.
Fluctuation resulting in an average of low temperatures could possibly indicate both poor adrenal and thyroid function.