Yes! The often-cited “normal body temperature” traces back to Carl Wunderlich’s seminal 1868 study, which measured axillary temperatures in thousands of hospitalized patients and reported an average temperature of 98.6°F (37°C), with an upper limit of 100.4°F (38°C).¹ However, recent evidence suggests a decline in body temperature of about 0.05°F (0.03°C) per decade over the past 150 years², prompting us to redefine “normal” temperature.

More specifically, a 2023 study of outpatients (mean age 52.7 years) found a mean oral temperature of 97.95°F (36.6°C) (95% range 96.7°F-99.2°F).³ The study also found that normal oral temperature declines with age, is lower in men than in women, and peaks in the late afternoon. 

Similarly, among non-infected hospitalized patients (mean age 61 years), a 2021 study reported a mean oral temperature of 98.0°F (36.7°C) (99% range 95.8°F-99.9°F),⁴ and a 2025 study in hospitalized adults concluded that the oral temperature threshold for fever should be 98.4°F (36.9°C) for those ≥85 years old.⁵

Additionally, the Infectious Diseases Society of America (IDSA) has recommended that for older adults in long-term care facilities, an oral temperature of 99°F (37.2°C) may indicate fever when observed across multiple measurements. ⁶ It also suggested that the most accurate method for establishing fever in older adults is a temperature elevation of >2°F (>1.1°C) above baseline, though this requires knowledge of the patient’s baseline temperature.⁶

Potential explanations for the decline in our body temperature—which reflects our basal metabolic rate— over the past 150 years include decreased prevalence of chronic infections (e.g., tuberculosis), improved sanitation, widespread use of anti-inflammatory medications, and even decreased physical activity! ^{3, 7}

So, we should “personalize” the definition of fever and lower its threshold by 0.5°F, or as much as 2.0°F, depending on patient demographics and clinical settings. When repeated and confirmed, an oral temperature of 99.4°F (37.4°C) in our 91-year-old patient should not be automatically dismissed as “normal.” 

 Bonus pearl: Did you know that for his study, Carl Wunderlich measured axillary temperatures— a method now known to be less accurate than oral or rectal measurements— by utilizing a foot-long thermometer that required 20 minutes to register? ⁸

Contributed by Khaled Said, 4th year Medical Student, Ponce Health Sciences University School of Medicine, St. Louis, Missouri 

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References

1. Mackowiak PA. Concepts of Fever. Arch Intern Med.1998;158(17):1870–1881.
2. Myroslava P, Catherine L, Joanna L, Trevor H, Julie P. Decreasing human body temperature in the United States since the Industrial Revolution. ELife. 2020; 9:e49555
3. 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. 2023;183(10):1128–1135.
4. Speaker SL, Pfoh ER, Pappas MA, Hu B, Rothberg MB. Oral Temperature of Noninfected Hospitalized Patients. 2021;325(18):1899–1901.
5. Émond JP, Cheung VW, Brial A, Nguyen QD. Age-Adjusted Oral Temperature Thresholds for Rectal Fever Diagnosis in Hospitalized Older Adults. J Am Med Dir Assoc. 2026;27(2):106044.
6. Rowe TA, Jump RLP, Andersen BM, et al. Reliability of nonlocalizing signs and symptoms as indicators of the presence of infection in nursing-home residents. Infection Control & Hospital Epidemiology. 2022;43(4):417-426.
7. Yegian AK, Heymsfield SB, Lieberman DE. Historical body temperature records as a population-level ‘thermometer’ of physical activity in the United States. Curr Biol. 2021;31(20):R1375-R1376.
8. Haidar G, Singh N. Fever of unknown origin. N Engl J Med. 2022;386(5):463-477.

Disclosures/Disclaimers: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!