Body Temperature

by | Apr 23, 2024 | Nurse Article | 0 comments

Vital signs are a basic component of assessment of physiological and psychological health of a client. Body temperature, pulse, respiration and blood pressure are the signs of life.

Body temperature may be defined as the degree of heat maintained by the body, or it is the balance between the heat produced and the heat lost in the body.

The regulation of the body is maintained by two mechanisms:

Thermogenesis: a chemical regulation by the production of heat.

Thermolysis: a physical regulation by loss of heat.

The heat regulating centre is the hypothalamus situated in the brain. Heat is produced in the body continuously. Unless it is lost from the body, no balance can be maintained.

Ways of Producing Heat in the Body

Oxidation of food: during metabolism of protein, carbohydrate and fat, heat is produced as a by-product.

Specific Dynamic Action of Food

There is an increase in the production of energy in the form of heat after taking food. This is not due to the work in digestion or absorption but is due to the stimulating effect of food on basal metabolism. It is knows as specific dynamic action of food.


During exercise heat is produced faster than it is eliminated from the body. The heavier the exercise, the greater will be production of heat in the body. During exercise, the blood supply to the skin is increased and the individual feels hot.

Strong Emotions

Excitement, anxiety, nervousness etc., stimulate the autonomic nervous system which causes stimulation of the different organs in the body including the secreting glands.

Hormonal Effect

Increased activity of the thyroid gland and the adrenal gland raises the body temperature. Ovarian hormone (progesterone) produces a rise in the body temperature.


Change in the Environmental and Atmospheric Conditions

High room temperature increases the body temperature (by preventing the evaporation process).

Diseased Conditions

Fever or pyrexia is caused by the bacterial invasion. It is the protective action of the body against the invading bacteria. The degree of temperature depends upon the severity of infection.

Ways of Losing Heat from the Body

The heat is lost from the body through different organs:

Through the skin

The skin acts as one of the important organs in the heat regulation. It is controlled by the hypothalamus. When the body temperature is increased, the warm blood flows through the hypothalamus. The hypothalamus which is very sensitive to heat variations in the blood, send impulses to the skin, causing vasodilation. Due to vasodilation, more blood comes to the skin and the heat is lost by means of conduction, convection, radiation and evaporation by mostly by radiation.

Through the Lungs

The temperature of the air which is taken to the lungs is that of the atmosphere and it is lower than that of the body temperature. On entering the respiratory tract, it is warmed to that of the body temperature by absorbing heat from the lung tissue. As the individual breathes out, the warmed air is lost through the expired air. Some of the body fluid is also vaporized and is lost through the expired air. Approximately 300 ml of water is also vaporized from the lung daily.

Through the Kidneys

The kidneys secrete urine which is warmed by the heat taken from the body. As the urine is excreted, the heat is also lost from the body.

Through the Bowels

The faeces that are formed in the bowel absorb heat from the body. So when an individual defecates, the heat is also lost from the body.


In a healthy individual, the body temperature may vary between 36.1 to 37.2 degree celcius. The following factors influence the variations in the body temperature.

Time of the day: it is less in the morning and more in the evening.

Time of the month: menstruation causes a sudden fall in the temperature and rises slowly after ovulation to a maximum just before the next menstrual period.

Age of the person: young people have higher temperature than the old people.

Part of the body where the temperature is taken: the temperature is highest when taken by rectum. The temperature is lowest when taken by axilla.

Oral temperature: 37 degree celcius

Rectal temperature: 37.5 degree celcius

Axillary temperature: 36.4 degree celcius

Emotions: the temperature may vary in persons with strong emotions.

Exercise: a heavy exercise increases the body temperature. Rest and sleep reduces the body temperature.

Environmental factors: hold and cold environment, hot and cold bath etc., may influence the body temperature.


Body temperature can be assessed with a variety of devices.

Glass Thermometer/Clinical Thermometer

A clinical thermometer is a special instrument designed to measure the temperature of the body. It is available in both Fahrenheit and Celcius (centigrade) scales. The thermometer has two parts, a bulb containing mercury and a stem in which the mercury can rise. On the stem is a graduated scale representing the degree of temperature, the lowest registered being 35 degree celcius. The highest being 43.3 degree celcius, because the body temperature above or below these points are rare.

The bulbs are of different sizes and shapes. Greater the surface of the glass, surrounding the mercury, more rapidly the mercury is heated up, thus more rapidly the thermometer registers. The oral thermometer are with long and slender bulbs and they register more rapidly than the rectal thermometer with short and fat bulbs. The rectal thermometers often have colored bulbs.

The clinical thermometers are different from the lotion thermometers:

There is no constriction in the lotion thermometer. Therefore, the mercury falls down on cooling. In the clinical thermometer, due to presence of a constriction, the mercury never falls unless it is shaken, so the reading can be done conveniently.
The grading on the lotion thermometers are from the freezing point to the boiling point of the water (0 to 100 degree celcius). The grading on the clinical thermometers is from 35 to 43.3 degree celcius.

1/ To shake the mercury down, grasp the thermometer securely by the upper end of the stem and never hold it by the bulb. Shake it down by the quick movement of the wrist.

2. Be careful not to let the thermometer fall or strike against anything. Move away from the articles before shaking the thermometers.

3. The thermometers are never washed with hot water, because the heat expands the mercury beyond the capacity of the stem and the thermometer can break.

4. When storing the thermometers, never store them in disinfectant solution. Rinse them in clean water, dry the bulb and stem and put them in their containers with the bulb down resting on smooth surfaces (cotton).

5. For fear of breaking thermometers, never place the thermometers in the mouth, or who is not able to hold the thermometer in place.

The thermometers used in common should be washed with soap and water and disinfected with a good disinfectant:
Electronic Thermometer:

There are many types of electronic thermometers, but all have similar characteristics. The thermometer consists of a battery-powered control unit and a temperature-sensitive probe connected to the control unit by a thin cord. When in use, a disposable plastic sheath covers the probe to prevent transmission of infection.

These thermometers provide reading in less than 60 seconds. They offer a convenient, safe, accurate and fast method for measuring temperature. The reading is quickly displayed on the unit and is easy to read.

An electronic thermometer can be used for oral, axillary or rectal temperature measurements and it can be used with multiple clients. The disadvantage of electronic thermometers is their high cost and the need for regular maintenance.

Tympanic Membrane Thermometers

It is a portable, hand held device, resembling an otoscope that recharges using a battery pack. It records temperature using a sensor probe that is placed in the ear canal to detect infrared radiation from the ear drum. It is appropriate for infants over 2 months or very young children who may find it difficult to remain still, when other methods are used. This is also useful in departments where quick assessment is necessary such as emergency/causality departments since the recording is available in 2 seconds. It should not be used in clients who have ear drainage or scarred tympanic membranes.

Disposable Paper Thermometer

Single use paper thermometers are thin strips of chemically treated paper with raised dots that change color to reflect the temperature usually in less than 1 min. These thermometers are available in Celcius and Fahrenheit scale.

Temperature Sensitive Strips and Chemical Dot

These can be used to obtain a general indication of body surface temperature. They are usually placed on the forehead or abdomen. The skin under the strip must be dry. After a specified period of time, the strip changes its color. The strip is removed and discarded after the color change is noted.

The Common Sites for Taking Body Temperature

To get accurate measurement of the body temperature, the bulb of the thermometer must be placed where it can be completely surrounded by body tissue and where there are blood vessels situated near the surface. The temperature may vary if the bulb of the thermometer comes in contact with clothing, air, moisture etc. the common sites for taking body temperature are mouth, axilla, groin, vagina and rectum.

Temperature of Mouth


1. Since there is a good blood supply under the tongue, more or less a correct body temperature can be recorded.

Disadvantages: the nurse may not know whether the bulb of the thermometer is in place. Instead of keeping it in touch with the under surface of the tongue, the client may keep it in the air of the mouth cavity. Thus, there is a possibility of recording a false temperature.

2. There is less chance for the bulb coming in contact with the outside air.

Disadvantage: the children or insensible person may bite the thermometer thus there is a chance of breaking the thermometer.

3. The thermometer can be held easily under the tongue, so there is less chance of the thermometer falling down from the mouth, provided the mouth is closed.

Disadvantage: if the thermometers are not adequately disinfected, there is always the possibility of cross infection.

4. To take the temperature by mouth no privacy is needed.

Disadvantage: if the disinfectant is not removed completely from the thermometers, the clients will get the bad taste of the disinfectant. The clients will get tired if the thermometer is kept for a long time.


1. The temperature is not taken by mouth in the following clients:

2. Clients have nervous, delirious, unconscious, hysterical and mentally confused and those who cannot follow instructions.

3. Convulsions

4. Mouth breather

5. Injuries, inflammation or operations of mouth

6. Extremely weak persons

7. Frequent attack of cough

8. Children under 6 years of age


Temperature by Axilla


1. Taking temperature by axilla causes less discomfort for the client.

Disadvantage: the axilla is mostly moist from perspiration. Presence of moisture give a false reading.

2. In children and other clients who are not able to hold the thermometer in the mouth, this method may be used since the nurse will be able to keep it in position without difficulty.

Disadvantages: if the thermometer is not placed correctly, the bulb of the thermometer may go beyond the axilla and remain in the air or in contact with the clothing and it may give a false reading.

3. Taking hot or cold drinks will not affect the temperature reading.

Disadvantage: with the above reasons the axillary method is least reliable.

4. The client does not get the ill taste of the disinfectants. There is no biting the thermometers.


Temperature by Rectum


1. The rectal method is used when the oral method is contraindicated.

Disadvantage: the client needs privacy.

2. The rectal method is most reliable. Rectum contains a large amount of blood supply and it is not influenced by the external air. If the thermometer is positioned correctly, it will be fully surrounded by the body tissue and we get a more accurate reading.

Disadvantage: if the rectum is loaded with faecal matter, we get a false reading.


1. The rectal temperature should not be taken in the following clients:

2. Clients had rectal surgery or inflammation of the rectum

3. The clients who having diarrhea

4. When the rectum is packed with faecal matter

5. The clients who are having some kind of treatments, e.g. bowel wash, enema etc.


Temperature by Ear

Since the development of tympanic membrane thermometer, the ear has been added as a site where temperature can be easily and safely measured.


1. The tympanic membrane its blood supply from the same vasculature that supplies the hypothalamus. Thus tympanic temperature reflects the core body temperature.

2. The ear is readily accessible.

3. It permits rapid temperature readings in very young confused or unconscious clients.

4. As the ear canal has fewer pathogens than the oral or rectal cavities, infection control is less of a concern with the tympanic site.

5. Cerumen in the ear canal on the presence of otitis media does not significantly alter temperature readings.

6. Smoking, drinking and eating which slightly alter oral temperature measurement but do not affect tympanic temperature measurement.


To obtain an accurate measurement, snugly fit the probe in the client’s ear canal and angle it towards the client’s jaw line.


Frequency of Taking Temperature in the Hospital

Frequency of taking temperature is determined by the condition of the client. For clients who are not seriously ill, it need to be taken in the morning and evening. The temperature is to be checked every 4 hours or even more frequently for those who are acutely ill, who are having high fever, and post operative clients. If the temperature is taken by rectum or axilla, it should be specified in the chart.