From the Guidelines
The average normal body temperature for a healthy adult human is approximately 98.6 degrees Fahrenheit (37 degrees Celsius), but recent evidence suggests that this value has been decreasing over time, with a current normal body temperature range subject to various factors such as age, gender, and diurnal variation 1.
Factors Influencing Body Temperature
Normal body temperature can actually range between 97°F (36.1°C) and 99°F (37.2°C) and still be considered within normal limits. Body temperature naturally fluctuates throughout the day, typically being lowest in the early morning and highest in late afternoon or evening. Various factors can influence an individual's temperature, including:
- Physical activity
- Environmental conditions
- Hormonal changes
- The body's metabolic rate
Thermoregulation
The body maintains this temperature through thermoregulation, a process controlled by the hypothalamus in the brain that balances heat production and heat loss to keep core temperature within the optimal range for cellular function and enzymatic reactions.
Definition of Fever
A temperature above 100.4°F (38°C) is generally considered a fever, while hypothermia occurs when body temperature drops below 95°F (35°C) 1. However, the definition of fever can vary depending on the context, such as in patients with neutropenia or in ICU patients, where a single oral temperature greater than or equal to 38.3°C or greater than 38.0°C sustained over at least 1 hour may be considered a fever 1.
Clinical Implications
It's essential to note that not all patients with infection manifest fever, and the absence of fever in patients with infection is associated with worse outcomes 1. Therefore, clinicians should consider a comprehensive evaluation for infection in patients with suspected infection, regardless of the presence of fever.
From the Research
Average Body Temperature
- The average body temperature of a human being is a topic of ongoing research, with various studies providing different estimates 2, 3, 4, 5.
- A study published in 2021 found that the mean temperature across all participants was 36.1°C (97.0°F), which is lower than the commonly cited average of 37.0°C (98.6°F) 2.
- Another study published in 2006 discussed the historical work of Wunderlich on temperature and the origins of the concept that a healthy normal temperature is 98.6 degrees F (37.0 degrees C) 3.
- A 2015 review estimated that oral temperature in normal healthy adults varies between 36.1°C and 37.2°C 4.
- A study conducted in Pakistan in 2008 found that the range for normal oral temperatures fell between 97 degrees F to 99.8 degrees F (mean 98.4 degrees F) 5.
Factors Affecting Body Temperature
- Body temperature can be affected by various factors, including age, sex, ambient temperature, and time of day 2, 3, 5.
- Women tend to have higher body temperatures than men, according to some studies 2, 5.
- There is no significant age-related variation in body temperature, but younger adults may experience larger variability in temperature over days 2.
- Ambient temperature can also impact body temperature, with higher temperatures potentially leading to increased conflicts and mental health issues 6.
Measurement and Variability
- Body temperature can be measured using various methods, including oral and axillary thermometers 5.
- There can be significant variability in body temperature between individuals, with some people having a lower normal temperature than others 2.
- Using a standardized "normal" temperature can lead to errors in diagnosis and treatment, highlighting the need for personalized body temperature measurements 2.