One size does not fit all: Assuming the same normal body temperature for everyone is not justified

Area of Science:

• Physiology
• Biomedical Science

Background:

• The standard estimate for normal human body temperature, 37.0°C (98.6°F), has remained largely unchanged despite advances in personalized medicine.
• Significant individual variations in body temperature exist, yet a standardized threshold is commonly used for clinical assessments.

Purpose of the Study:

• To investigate inter-individual and intra-individual thermal variability in oral body temperature.
• To determine if a substantial percentage of individuals exhibit mean oral temperatures below 37.0°C (98.6°F).
• To analyze how factors such as sex, age, time of day, ethnicity, body mass index (BMI), and menstrual phase influence body temperature.

Main Methods:

• Oral temperature measurements were taken 14 times over two weeks (7 morning, 7 evening) using digital thermometers in 96 adults (ages 18-67).
• Data were collected from 42 men and 54 women, including 27 couples and 42 singletons.
• Statistical analysis was performed to assess temperature differences based on various demographic and physiological factors.

Main Results:

• Mean oral temperatures ranged from 35.2°C (95.4°F) to 37.4°C (99.3°F), with an overall average of 36.1°C (97.0°F).
• 77% of participants had mean temperatures at least 0.55°C (1°F) lower than 37.0°C (98.6°F).
• Women exhibited higher temperatures than men; temperature variability was greater in younger adults but did not differ by sex.

Conclusions:

• The findings challenge the universal applicability of 37.0°C (98.6°F) as a normal body temperature, highlighting significant individual variations.
• Relying on a standardized normal temperature can lead to misdiagnosis of fever or false negatives, particularly in contexts like COVID-19 screening.
• Personalized body temperature baselines, established through regular monitoring, are essential for accurate clinical decision-making and health tracking.