Why is it necessary to have a normal temperature range? Why isn’t a temperature of 98.6º F normal and everything else is abnormal? The reason is that a person can have a body temperature that is slightly above or below 98.6 F and still be normal and healthy.

Some of the factors that make it necessary that “normal” temperature be defined as a range are given below.

a. People Have Different “Normal Temperatures.”

Remember that 98.6º F is the average normal temperature. Some people have normal temperature that is slightly higher than average while others have normal temperature that is slightly lower than average.

(1) A person whose normal body temperature is above average (such as 99.0º F) is said to have a “high-normal” body temperature.

(2) A person whose normal body temperature is below average (such as 97.6º F) is said to have a “low-normal” body temperature.

b. Menstrual Cycle Affects Body Temperature.

A woman’s body temperature drops slightly before ovulation, rises about 1º F above normal during ovulation, and then returns to her normal level.

c. Pregnancy Affects Body Temperature.

During pregnancy, a woman’s body temperature stays above her regular normal temperature.

d. Physical Activity Affects Body Temperature.

When a person exercises or does hard work, his muscles change stored energy supplies in the body (mainly glucose and fat) into usable energy. When the body’s muscles change stored energy into usable energy, heat is given off. This is why you can warm up in cold weather by doing exercises.

e. Age Affects Body Temperature.

(1) A newborn baby has some difficulty in adjusting his body temperature. His temperature may be slightly high one time and slightly low the next. By the time, the baby is one year old, the parts of his body that control his body temperature are fully developed and his normal body temperature has been established.

(2) An elderly person will usually have a low-normal body temperature. The lower body temperature is caused by changes within his body and by a decrease in physical activity.

f. Weather Affects Body Temperature.

When a person’s body is exposed to hot weather, his body temperature rises. When a person’s body is exposed to cold weather, his body temperature drops. In the cold environment the body loses heat in the following five ways.

(1) Conduction. Conduction is the direct transfer of heat from a part of the body to a colder object. For example, when a warm hand touches cold metal or ice, or when a person’s hand is immersed in water with a temperature below his body temperature. Heat passes directly from the body to the colder object.

(2) Convection. Convection occurs when heat is transferred to circulating air, as when cool air moves across the surface of a person’s body. A person who is standing outside in windy winter weather and who is wearing lightweight clothing is losing heat to the environment mostly by convection.

(3) Evaporation. Evaporation is the conversion of any liquid to a gas. The evaporation process requires energy (heat). Evaporation is the natural mechanism by which sweating cools the body. This is why swimmers coming out of the water feel a sensation of cold as the water evaporates from their skin. Individuals who exercise vigorously in a cool environment may sweat and feel warm at first, but later, as their sweat evaporates, they can become exceedingly cool.

(4) Radiation. Radiation is the loss of body heat directly to colder objects in the environment. Because heat always travels from a warm object to a cooler one, a person standing in a cold room will lose heat by radiation.

(5) Breathing. Breathing causes body heat to be lost as warm air in the lungs is exhaled into the atmosphere and cooler air is inhaled.

NOTE: If a person is working in an area that is hot due to the type of work being done, such as in a steel mill, his body temperature will rise since the hot environment is his “weather.”

g. Time of Day Affects Body Temperature.

A person’s body temperature is usually lower in the morning than in the afternoon. This change is mainly due to warmer weather and more physical activity occurring later in the day.

h. Emotions Affect Body Temperature.

A person that is excited (joyful, scared, angry, and so forth.) will have an increase in body temperature. The excitement causes the body to increase the rate at which it changes stored food (glucose and fat) into usable energy. As the energy output increases, so does the amount of heat produced by the body.

i. Place of Measurement Affects Measurement.

The three locations normally used in determining the body temperature are the mouth (oral temperature), the rectum (rectal temperature), and the armpit (axillary temperature). If you measured a person’s body temperature using all three of these methods, you would obtain three slightly different temperatures.

The axillary (armpit) temperature would be slightly lower than the oral (mouth) temperature while the rectal (rectum) temperature would be slightly higher than the oral temperature.

The rectal temperature is considered an essential measurement in the hypothermic (cold injury) or hyperthermic (heat injury) patient. All other methods of obtaining the body temperature are not considered accurate for the pre-hospital or battlefield environment when dealing with environmental injuries. The oral and axillary methods should be used for the clinical or field sick call settings only.