The human body’s core temperature (internal body temperature) is measured in degrees Celsius (ºC) or Fahrenheit (ºF). In Canada, degrees Celsius is most commonly used.

In adults, the normal core body temperature (referred to as normothermia or afebrile) is 36.5–37.5ºC or 97.7–99.5ºF (OER #2).

A wider temperature range is acceptable in infants and young children, and can range from 35.5–37.7ºC or 95.9–99.8ºF. Infants and children have a wider temperature range because their heat control mechanisms are less effective. They are at risk for heat loss for many reasons including having less subcutaneous fat than adults, a larger body surface area in comparison to weight (and larger head size in proportion to the rest of the body), immature metabolic mechanisms (e.g., they may be unable to shiver), and limited ability to produce heat through activity. They are also at risk of excessive heat production due to crying and restlessness as well as external factors such as being wrapped in too many blankets.

Older adults tend to have lower body temperatures and are at risk for hypothermic states; reasons for this may include having less subcutaneous tissue acting as insulation, loss of peripheral vasoconstriction capacity, decreased cardiac output with resultant lowered blood flow to the extremities, decreased muscle mass resulting in reduced heat production capacity, and decreased metabolic responses.

See Table 2.1 for normal temperature ranges based on method. The normal ranges vary slightly for each of the methods. It is important to consider a client’s baseline temperature as some individuals present with a temperature slightly above or below these ranges. To make an informed clinical judgement, examine the client’s records to determine a trend in temperature. A pattern of high or low temperature findings may reveal a baseline for your client. As a healthcare provider, it is important to determine the significance of the temperature by also considering influencing factors and the client’s overall state of health.

Other factors that influence temperature include diurnal rhythm, exercise, stress, menstrual cycle, and pregnancy. The diurnal cycle causes a fluctuation of 1ºC, with temperatures lowest in the early morning and highest in the late afternoon. During exercise, body temperature rises because the body is using energy to power the muscles. Temperature can rise as a result of stress and anxiety, due to stimulation of the sympathetic nervous system and increased secretion of epinephrine and norepinephrine. Body temperature varies throughout a woman’s menstrual cycle due to hormonal fluctuations, rising after ovulation until menstruation by about 0.5–1ºC. Body temperature is slightly elevated during pregnancy as a result of increased metabolism and hormone production such as progesterone.

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Chapter Attributions

Part of this content was adapted from OER #2 (as noted in brackets above):

• © Apr 10, 2017 OpenStax Anatomy and Physiology. Textbook content produced by OpenStax Anatomy and Physiology is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/7c42370b-c3ad-48ac-9620-d15367b882c6@12