Breaking the myth: Normal human body temperature isn't universally 98.6°F

Doctors and patients worldwide have the notion that the normal temperature of human body is 98.6 Fahrenheit or 37°C. However recent findings from a cross-sectional study published in September issue of JAMA Intern Med have shown otherwise. The results of the study on 126 705 patients, showed that average body temp was 97.952 or 36.64 °C, breaking the myth around the general perception.The results also indicated that age, sex, height, weight, and time of day are factors that contribute to variations in individualized normal temperature ranges.

Although oral temperature is commonly assessed in medical examinations, the range of usual or “normal” temperature is poorly defined. To address this knowledge gap, researchers from Stanford University School of Medicine in collaboration with researchers from University of Southern California and Karolinska Institutet tried to determine normal oral temperature ranges by age, sex, height, weight, and time of day.

The study used clinical visit information from the divisions of Internal Medicine and Family Medicine in a single large medical care system. All adult outpatient encounters that included temperature measurements from April 28, 2008, through June 4, 2017, were eligible for inclusion.  

The LIMIT filtering algorithm was applied to iteratively remove encounters with primary diagnoses overrepresented in the tails of the temperature distribution, leaving only those diagnoses unrelated to temperature. The 396195 encounters included in the analysis set consisted of 126 705 patients, mean age, 52.7 years. 

Prior to running LIMIT, the mean (SD) overall oral temperature was 98.078 Fahrenheit or 36.71 °C; following LIMIT, the mean temperature was 97.952 Fahrenheit or 36.64 °C. Using mixed-effects modeling, age, sex, height, weight, and time of day accounted for 6.86% (overall) and up to 25.52% (per patient) of the observed variability in temperature. Mean normal oral temperature did not reach 98.6 Fahrenheit or 37 °C for any subgroup.

The authors noted that the clinical significance of a value outside of the usual range is an area for future study.

Reference: Ley C, Heath F, Hastie T, Gao Z, Protsiv M, Parsonnet J. Defining Usual Oral Temperature Ranges in Outpatients Using an Unsupervised Learning Algorithm. JAMA Intern Med. Published online September 05, 2023. DOI: 10.1001/jamainternmed.2023.4291