Normal human body temperature
Encyclopedia
Normal human body temperature, also known as normothermia or euthermia, is a concept that depends upon the place in the body
at which the measurement is made, and the time of day and level of activity of the person. There is no single number that represents a normal or healthy temperature for all people under all circumstances using any place of measurement.
Different parts of the body have different temperatures. Rectal and vagina
l measurements, or measurements taken directly inside the body cavity, are typically slightly higher than oral measurements, and oral measurements are somewhat higher than skin temperature. The commonly accepted average core body temperature (taken internally) is . The typical oral (under the tongue) measurement is slightly cooler, at , or . Although some people think of these numbers as representing the normal temperature, a wide range of temperatures has been found in healthy people. In samples of normal adult men and women, the observed range for oral temperature is 33.2 –, for rectal it is 34.4 –, for the tympanic cavity
it is 35.4 – and for axillary it is 35.5 –.
The time of day and other circumstances also affects the body's temperature. The core body temperature of an individual tends to have the lowest value in the second half of the sleep cycle; the lowest point, called the nadir, is one of the primary markers for circadian rhythm
s. The body temperature also changes when a person is hungry, sleepy, or cold.
In 1861, Carl Reinhold August Wunderlich
released his summary of the armpit, or axillary, temperatures of twenty five thousand people, and reported the mean to be 37 °C (98.6 °F), with a range of 36.25 °C (97.3 °F) to 37.5 °C (99.5 °F). He also identified the natural variations in temperature throughout the day and the variations between individuals, as well as differences based on sex and age, which were largely ignored in favor of an oversimplified single number. Wunderlich's thermometers were not calibrated to a standard setting—in 1861, no standard had been agreed upon—and he never explained his methods for compiling and describing the data he had collected, which would have been a monumental task before the availability of basic calculating machines. The one surviving, hand-made thermometer reads significantly higher than modern thermometers.
) is part of a homeostatic mechanism that keeps the organism at optimum operating temperature
, as it affects the rate of chemical reaction
s. In human
s the average oral temperature is 37 °C (98.6 °F), though it varies among individuals. However, no person always has exactly the same temperature at every moment of the day. Temperatures cycle regularly up and down through the day, as controlled by the person's circadian rhythm
. The lowest temperature occurs about two hours before the person normally wakes up. Additionally, temperatures change according to activities and external factors.
Normal body temperature may differ as much as from day to day.
Body temperature is sensitive to many hormones, so women have a temperature rhythm that varies with the menstrual cycle
, called a circamensal rhythm. A woman's basal body temperature
rises sharply after ovulation, as estrogen
production decreases and progesterone
increases. Fertility awareness
programs use this predictable change to identify when a woman is able to become pregnant. During the luteal phase
of the menstrual cycle, both the lowest and the average temperatures are slightly higher than during other parts of the cycle. However, the amount that the temperature rises during each day is slightly lower than typical, so the highest temperature of the day is not very much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about .
Temperature also varies with the change of season
s during each year. This pattern is called a circannual rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns.
Increased physical fitness increases the amount of daily variation in temperature.
With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. Elderly patients may have a decreased ability to generate body heat during a fever, so even a somewhat elevated temperature can indicate a serious underlying cause in geriatrics
.
Generally, oral, rectal, gut, and core body temperatures, although slightly different, are well-correlated, with oral temperature being the lowest of the four.
Oral temperatures are influenced by drinking, chewing, smoking, and breathing with the mouth open. Cold drinks or food reduce oral temperatures; hot drinks, hot food, chewing, and smoking raise oral temperatures.
Axillary (armpit), tympanic (ear), and other skin-based temperatures correlate relatively poorly with core body temperature. Tympanic measurements run higher than rectal and core body measurements, and axillary temperatures run lower. The body uses the skin as a tool to increase or decrease core body temperature, which affects the temperature of the skin. Skin-based temperatures are more variable than other measurement sites. The peak daily temperature for axillary measurements lags about three hours behind the rest of the body. Skin temperatures are also more influenced by outside factors, such as clothing and air temperature.
Temperature is increased after eating or drinking anything with calories. Caloric restriction, as for a weight-loss diet, reduces overall body temperature. Drinking alcohol
reduces the amount of daily change, slightly lowering daytime temperatures and noticeably raising nighttime temperatures.
Exercise raises body temperatures. In adults, a noticeable increase usually requires strenuous exercise or exercise sustained over a significant time. Children develop higher temperatures with milder activities, like playing.
Psychological factors also influence body temperature: a very excited person often has an elevated temperature.
Wearing more clothing slows daily temperature changes and raises body temperature. Similarly, sleeping with an electric blanket
raises the body temperature at night.
Sleep disturbances also affect temperatures. Normally, body temperature drops significantly at a person's normal bedtime and throughout the night. Short-term sleep deprivation
produces a higher temperature at night than normal, but long-term sleep deprivation appears to reduce temperatures. Insomnia
and poor sleep quality are associated with smaller and later drops in body temperature. Similarly, waking up unusually early, sleeping in, jet lag
and changes to shift work
schedules may affect body temperature.
and can be lowered, if desired, with antipyretic
medications.
An organism at optimum temperature is considered afebrile or apyrexic, meaning "without fever". If temperature is raised, but the setpoint is not raised, then the result is hyperthermia
.
In a medical setting, mild hyperthermia is commonly called heat exhaustion or heat prostration; severe hyperthermia is called heat stroke. Heat stroke may come on suddenly, but it usually follows the untreated milder stages. Treatment involves cooling and rehydrating the body; fever-reducing drugs are useless for this condition. This may be done through moving out of direct sunlight to a cooler and shaded environment, drinking water, removing clothing that might keep heat close to the body, or sitting in front of a fan. Bathing in tepid or cool water, or even just washing the face and other exposed areas of the skin, can be helpful.
With fever, the body's core temperature rises to a higher temperature through the action of the part of the brain that controls the body temperature; with hyperthermia, the body temperature is raised without the consent of the heat control centers.
. Symptoms usually appear when the body's core temperature drops by - (-) below normal temperature.
, and this can be used for family planning
.
of an organism
, specifically in deep structures of the body such as the liver
, in comparison to temperatures of peripheral tissues. Core temperature is normally maintained within a narrow range so that essential enzymatic reactions can occur. Significant core temperature elevation (hyperthermia
) or depression (hypothermia
) that is prolonged for more than a brief period of time is incompatible with human life.
Temperature examination in the rectum
is the traditional gold standard
measurement used to estimate core temperature (oral temperature is affected by hot or cold drinks and mouth-breathing). Rectal temperature is expected to be approximately one Fahrenheit degree higher than an oral temperature taken on the same person at the same time. Ear thermometers measure eardrum temperature using infrared
sensors. The blood supply to the tympanic membrane is shared with the brain
. However, this method of measuring body temperature is not as accurate as rectal measurement and has a low sensitivity for fevers, missing three or four out of every ten fevers in children. Ear temperature measurement may be acceptable for observing trends in body temperature but is less useful in consistently identifying fevers.
Until recently, direct measurement of core body temperature required surgical insertion of a probe, so a variety of indirect methods have commonly been used. While the rectal
or vaginal
temperature is generally considered to give the most accurate assessment of core body temperature, particularly in hypothermia, its recording is disliked by patients and medical staff alike. In the early 2000s, ingestible thermistor
s in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement.
Taking a patient's temperature
is an initial part of a full clinical examination. Sites used for measurement include:
The temperature reading depends on which part of the body is being measured. The typical daytime temperatures among healthy adults are as follows:
Normal human body temperature varies slightly from person to person and by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is . This means that any oral temperature between and ( and ) is likely to be normal.
The temporal artery is close to the surface of the skin and therefore accessible for reading. The temporal artery is linked to the heart by the carotid artery which is directly linked to the aorta. It forms part of the main trunk of the arterial system. So long as the patient’s blood flow is permanent and regular, the method allows precise measurement of the temperature.
or mercury
contents are poisonous. This is avoided by the use of electronic thermometers which are made from solid plastic and use a metal (thermocouple
) sensor.
A plastic thermometer strip placed on the forehead
gives an approximate local reading, which depends to a great extent on ambient air temperature and local circulation effects. Using a thermometer to record the temperature under the armpit is less affected by surrounding air temperature, but is still prone to diverge from true core temperature if there are alterations in blood circulation.
Since the year 2000, small ear thermometers have become available and it is thought that the eardrum
closely mirrors core temperature values. These work by detecting the infrared
heat emission from the tympanic membrane and a measurement is quickly taken within one second making them popular for use with children. While the electronic display of the temperature value is easier to read than interpreting the graduation marks on a thermometer, there are some concerns for the accuracy of ear thermometers in home use.
Human body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...
at which the measurement is made, and the time of day and level of activity of the person. There is no single number that represents a normal or healthy temperature for all people under all circumstances using any place of measurement.
Different parts of the body have different temperatures. Rectal and vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
l measurements, or measurements taken directly inside the body cavity, are typically slightly higher than oral measurements, and oral measurements are somewhat higher than skin temperature. The commonly accepted average core body temperature (taken internally) is . The typical oral (under the tongue) measurement is slightly cooler, at , or . Although some people think of these numbers as representing the normal temperature, a wide range of temperatures has been found in healthy people. In samples of normal adult men and women, the observed range for oral temperature is 33.2 –, for rectal it is 34.4 –, for the tympanic cavity
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....
it is 35.4 – and for axillary it is 35.5 –.
The time of day and other circumstances also affects the body's temperature. The core body temperature of an individual tends to have the lowest value in the second half of the sleep cycle; the lowest point, called the nadir, is one of the primary markers for circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
s. The body temperature also changes when a person is hungry, sleepy, or cold.
History
In the early 18th century, Daniel G. Fahrenheit originally used human body temperature as a reference point for his temperature scale, defining it to be 96°F. Later redefinition of his scale to use the boiling point of water as a reference point caused the numerical value for normal body temperature to drift.In 1861, Carl Reinhold August Wunderlich
Carl Reinhold August Wunderlich
Carl Reinhold August Wunderlich was a German physician, pioneer psychiatrist, and medical professor...
released his summary of the armpit, or axillary, temperatures of twenty five thousand people, and reported the mean to be 37 °C (98.6 °F), with a range of 36.25 °C (97.3 °F) to 37.5 °C (99.5 °F). He also identified the natural variations in temperature throughout the day and the variations between individuals, as well as differences based on sex and age, which were largely ignored in favor of an oversimplified single number. Wunderlich's thermometers were not calibrated to a standard setting—in 1861, no standard had been agreed upon—and he never explained his methods for compiling and describing the data he had collected, which would have been a monumental task before the availability of basic calculating machines. The one surviving, hand-made thermometer reads significantly higher than modern thermometers.
Variations
Temperature control (thermoregulationThermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
) is part of a homeostatic mechanism that keeps the organism at optimum operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
, as it affects the rate of chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s. In human
Human
Humans are the only living species in the Homo genus...
s the average oral temperature is 37 °C (98.6 °F), though it varies among individuals. However, no person always has exactly the same temperature at every moment of the day. Temperatures cycle regularly up and down through the day, as controlled by the person's circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
. The lowest temperature occurs about two hours before the person normally wakes up. Additionally, temperatures change according to activities and external factors.
Normal body temperature may differ as much as from day to day.
Natural rhythms
Body temperature normally fluctuates over the day, with the lowest levels around 4 a.m. and the highest in the late afternoon, around 4:00 p.m. (assuming the person sleeps at night and stays awake during the day). Therefore, an oral temperature of would, strictly speaking, be normal in the afternoon but not in the morning. An individual's body temperature typically changes by about between its highest and lowest points each day.Body temperature is sensitive to many hormones, so women have a temperature rhythm that varies with the menstrual cycle
Menstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
, called a circamensal rhythm. A woman's basal body temperature
Basal body temperature
Basal body temperature is the lowest temperature attained by the body during rest . It is generally measured immediately after awakening and before any physical activity has been undertaken, although the temperature measured at that time is somewhat higher than the true basal body temperature...
rises sharply after ovulation, as estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
production decreases and progesterone
Progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...
increases. Fertility awareness
Fertility awareness
Fertility awareness refers to a set of practices used to determine the fertile and infertile phases of a woman's menstrual cycle. Fertility awareness methods may be used to avoid pregnancy, to achieve pregnancy, or as a way to monitor gynecological health....
programs use this predictable change to identify when a woman is able to become pregnant. During the luteal phase
Luteal phase
The luteal phase is the latter phase of the menstrual cycle or the estrous cycle . It begins with the formation of the corpus luteum and ends in either pregnancy or luteolysis...
of the menstrual cycle, both the lowest and the average temperatures are slightly higher than during other parts of the cycle. However, the amount that the temperature rises during each day is slightly lower than typical, so the highest temperature of the day is not very much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about .
Temperature also varies with the change of season
Season
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...
s during each year. This pattern is called a circannual rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns.
Increased physical fitness increases the amount of daily variation in temperature.
With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. Elderly patients may have a decreased ability to generate body heat during a fever, so even a somewhat elevated temperature can indicate a serious underlying cause in geriatrics
Geriatrics
Geriatrics is a sub-specialty of internal medicine and family medicine that focuses on health care of elderly people. It aims to promote health by preventing and treating diseases and disabilities in older adults. There is no set age at which patients may be under the care of a geriatrician, or...
.
Variations due to measurement methods
Different methods used for measuring temperature produce different results.Generally, oral, rectal, gut, and core body temperatures, although slightly different, are well-correlated, with oral temperature being the lowest of the four.
Oral temperatures are influenced by drinking, chewing, smoking, and breathing with the mouth open. Cold drinks or food reduce oral temperatures; hot drinks, hot food, chewing, and smoking raise oral temperatures.
Axillary (armpit), tympanic (ear), and other skin-based temperatures correlate relatively poorly with core body temperature. Tympanic measurements run higher than rectal and core body measurements, and axillary temperatures run lower. The body uses the skin as a tool to increase or decrease core body temperature, which affects the temperature of the skin. Skin-based temperatures are more variable than other measurement sites. The peak daily temperature for axillary measurements lags about three hours behind the rest of the body. Skin temperatures are also more influenced by outside factors, such as clothing and air temperature.
Variations due to outside factors
Many outside factors affect the measured temperature as well. "Normal" values are generally given for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature ( to or to ), during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen to twenty minutes, as the temperature of the food, drink, or smoke can dramatically affect the reading.Temperature is increased after eating or drinking anything with calories. Caloric restriction, as for a weight-loss diet, reduces overall body temperature. Drinking alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
reduces the amount of daily change, slightly lowering daytime temperatures and noticeably raising nighttime temperatures.
Exercise raises body temperatures. In adults, a noticeable increase usually requires strenuous exercise or exercise sustained over a significant time. Children develop higher temperatures with milder activities, like playing.
Psychological factors also influence body temperature: a very excited person often has an elevated temperature.
Wearing more clothing slows daily temperature changes and raises body temperature. Similarly, sleeping with an electric blanket
Electric blanket
In the US the electric blanket is a blanket with an integrated electrical heating device usually placed above the top bed sheet. In the UK and Commonwealth, electric blanket commonly refers to an electric mattress pad, which is placed below the bottom bed sheet. Electric blankets usually have a...
raises the body temperature at night.
Sleep disturbances also affect temperatures. Normally, body temperature drops significantly at a person's normal bedtime and throughout the night. Short-term sleep deprivation
Sleep deprivation
Sleep deprivation is the condition of not having enough sleep; it can be either chronic or acute. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. It adversely affects the brain and cognitive function. Few studies have compared the...
produces a higher temperature at night than normal, but long-term sleep deprivation appears to reduce temperatures. Insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
and poor sleep quality are associated with smaller and later drops in body temperature. Similarly, waking up unusually early, sleeping in, jet lag
Jet lag
Jet lag, medically referred to as desynchronosis, is a physiological condition which results from alterations to the body's circadian rhythms; it is classified as one of the circadian rhythm sleep disorders...
and changes to shift work
Shift work
Shift work is an employment practice designed to make use of the 24 hours of the clock. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts....
schedules may affect body temperature.
Fever
A temperature setpoint is the level at which the body attempts to maintain its temperature. When the setpoint is raised, the result is a fever. Most fevers are caused by infectious diseaseInfectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
and can be lowered, if desired, with antipyretic
Antipyretic
Antipyretics ; an-tee-pahy-ret-iks; from the Greek anti, against, and pyreticus, are drugs or herbs that reduce fever. Normally, they will not lower body temperature if one does not have a fever. Antipyretics cause the hypothalamus to override an interleukin-induced increase in temperature...
medications.
An organism at optimum temperature is considered afebrile or apyrexic, meaning "without fever". If temperature is raised, but the setpoint is not raised, then the result is hyperthermia
Hyperthermia
Hyperthermia is an elevated body temperature due to failed thermoregulation. Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate...
.
Hyperthermia
Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate. It is usually caused by prolonged exposure to high temperatures. The heat-regulating mechanisms of the body eventually become overwhelmed and unable to deal effectively with the heat, causing the body temperature to climb uncontrollably. Hyperthermia at or above about is a life-threatening medical emergency that requires immediate treatment. Common symptoms include headache, confusion, and fatigue. If sweating has resulted in dehydration, then the affected person may have dry, red skin.In a medical setting, mild hyperthermia is commonly called heat exhaustion or heat prostration; severe hyperthermia is called heat stroke. Heat stroke may come on suddenly, but it usually follows the untreated milder stages. Treatment involves cooling and rehydrating the body; fever-reducing drugs are useless for this condition. This may be done through moving out of direct sunlight to a cooler and shaded environment, drinking water, removing clothing that might keep heat close to the body, or sitting in front of a fan. Bathing in tepid or cool water, or even just washing the face and other exposed areas of the skin, can be helpful.
With fever, the body's core temperature rises to a higher temperature through the action of the part of the brain that controls the body temperature; with hyperthermia, the body temperature is raised without the consent of the heat control centers.
Hypothermia
In hypothermia, body temperature drops below that required for normal metabolism and bodily functions. In humans, this is usually due to excessive exposure to cold air or water, but it can be deliberately induced as a medical treatmentTherapeutic hypothermia
Therapeutic hypothermia, also known as protective hypothermia, is a medical treatment that lowers a patient's body temperature in order to help reduce the risk of the ischemic injury to tissue following a period of insufficient blood flow. Periods of insufficient blood flow may be due to cardiac...
. Symptoms usually appear when the body's core temperature drops by - (-) below normal temperature.
Basal body temperature
Basal body temperature is the lowest temperature attained by the body during rest (usually during sleep). It is generally measured immediately after awakening and before any physical activity has been undertaken, although the temperature measured at that time is somewhat higher than the true basal body temperature. In women, temperature differs at various points in the menstrual cycleMenstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....
, and this can be used for family planning
Fertility awareness
Fertility awareness refers to a set of practices used to determine the fertile and infertile phases of a woman's menstrual cycle. Fertility awareness methods may be used to avoid pregnancy, to achieve pregnancy, or as a way to monitor gynecological health....
.
Core temperature
Core temperature, also called core body temperature, is the operating temperatureTemperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
of an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
, specifically in deep structures of the body such as the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, in comparison to temperatures of peripheral tissues. Core temperature is normally maintained within a narrow range so that essential enzymatic reactions can occur. Significant core temperature elevation (hyperthermia
Hyperthermia
Hyperthermia is an elevated body temperature due to failed thermoregulation. Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate...
) or depression (hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
) that is prolonged for more than a brief period of time is incompatible with human life.
Temperature examination in the rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
is the traditional gold standard
Gold standard (test)
In medicine and statistics, gold standard test refers to a diagnostic test or benchmark that is the best available under reasonable conditions. It does not have to be necessarily the best possible test for the condition in absolute terms...
measurement used to estimate core temperature (oral temperature is affected by hot or cold drinks and mouth-breathing). Rectal temperature is expected to be approximately one Fahrenheit degree higher than an oral temperature taken on the same person at the same time. Ear thermometers measure eardrum temperature using infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
sensors. The blood supply to the tympanic membrane is shared with the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. However, this method of measuring body temperature is not as accurate as rectal measurement and has a low sensitivity for fevers, missing three or four out of every ten fevers in children. Ear temperature measurement may be acceptable for observing trends in body temperature but is less useful in consistently identifying fevers.
Until recently, direct measurement of core body temperature required surgical insertion of a probe, so a variety of indirect methods have commonly been used. While the rectal
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
or vaginal
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
temperature is generally considered to give the most accurate assessment of core body temperature, particularly in hypothermia, its recording is disliked by patients and medical staff alike. In the early 2000s, ingestible thermistor
Thermistor
A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...
s in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement.
Methods of measurement
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
is an initial part of a full clinical examination. Sites used for measurement include:
- In the anus (rectal temperature)
- In the mouth (oral temperature)
- Under the arm (axillary temperature)
- In the ear (tympanic temperature)
- In the vaginaVaginaThe vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
(vaginal temperature) - On the skin of the forehead
- Over the temporal artery
- In the gut (by swallowing a small thermometer)
The temperature reading depends on which part of the body is being measured. The typical daytime temperatures among healthy adults are as follows:
- Temperature in the anus (rectum/rectal), vagina, or in the ear (otic) is about
- Temperature in the mouth (oral) is about
- Temperature under the arm (axillary) is about
Normal human body temperature varies slightly from person to person and by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is . This means that any oral temperature between and ( and ) is likely to be normal.
The temporal artery is close to the surface of the skin and therefore accessible for reading. The temporal artery is linked to the heart by the carotid artery which is directly linked to the aorta. It forms part of the main trunk of the arterial system. So long as the patient’s blood flow is permanent and regular, the method allows precise measurement of the temperature.
Measurement devices
There is a risk of injury from cracking the original glass thermometers if too much force is applied by the teeth to hold them in place and the alcoholAlcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
or mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
contents are poisonous. This is avoided by the use of electronic thermometers which are made from solid plastic and use a metal (thermocouple
Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...
) sensor.
A plastic thermometer strip placed on the forehead
Forehead
For the Arsenal striker see GervinhoIn human anatomy, the forehead is the fore part of the head. It is, formally, an area of the head bounded by three features, two of the skull and one of the scalp. The top of the forehead is marked by the hairline, the edge of the area where hair on the scalp...
gives an approximate local reading, which depends to a great extent on ambient air temperature and local circulation effects. Using a thermometer to record the temperature under the armpit is less affected by surrounding air temperature, but is still prone to diverge from true core temperature if there are alterations in blood circulation.
Since the year 2000, small ear thermometers have become available and it is thought that the eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
closely mirrors core temperature values. These work by detecting the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
heat emission from the tympanic membrane and a measurement is quickly taken within one second making them popular for use with children. While the electronic display of the temperature value is easier to read than interpreting the graduation marks on a thermometer, there are some concerns for the accuracy of ear thermometers in home use.