Important Information About Coronavirus and Body Temperature

Key Takeaways
Normal temperature varies widely.
Textbook 98.6º F is outdated.
Personal normal temperature is key.
Human body temperature is decreasing.
Factors influencing body temperature.
Location of temperature measurement matters.
Temperature not the sole indicator of infection.
Temperature readings can be ambiguous.
Frequently Asked Questions
References

Overview

As fever is a prominent indicator of the current health crisis, many individuals have hurried to acquire thermometers. Some establishments worldwide are even implementing temperature checks at entry points. While this practice may be suitable for the younger population, older individuals, who are most vulnerable to the health crisis, may not exhibit an elevated body temperature as easily. Moreover, what is considered a “normal” body temperature can vary significantly. Additionally, the measured temperature can vary based on the body part used for the assessment. Interestingly, the traditional "normal" body temperature of 98.6º F, established in 1868, is now regarded as outdated. This information may not be widely known yet, and it is likely that many individuals are unaware of this fact. In medical education, it is taught that the average core body temperature of humans is 98.6º F, a standard established over a century ago. However, research conducted over the years has shown that individuals have unique variations in various biological aspects, such as heart rate, blood pressure, organ size, hormone levels, and other physiological parameters. Despite these natural variations, the belief in 98.6º F as the "normal" body temperature remains unchanged. Yet, studies spanning more than sixty years suggest it is time to reconsider this conventional understanding.

We’re Getting Cooler

In a comprehensive review conducted in 1992, analyzing 27 studies spanning from 1935 to 1999, it was discovered that average normal body temperatures were lower than the traditional 98.6º F. Surprisingly, recorded normal temperatures obtained rectally, the most accurate method, ranged from 93.92º F to 100.04º F. This finding challenges the notion that temperature readings alone can reliably indicate one's health status, as individual baseline temperatures can vary significantly. For example, a slight increase from your personal normal temperature, such as going from 96º F to 99º F, could signify an infection. Without knowledge of your individual baseline, detecting such changes may prove challenging. Subsequent research in 2017 examined temperature readings from 35,488 patients, revealing a range of 95.54º F to 99.86º F, with an average of 97.88º F. A recent extensive study analyzed data from different time periods and found that individuals born in the early to mid-1990s exhibited an average body temperature 1.06º F lower than those born in the early 1800s for men and 0.58º F lower for women born in the 1990s compared to the 1890s. Julie Parsonnet, MD, a professor of medicine at Stanford University, leading the study, emphasized that the longstanding belief in a normal temperature of 98.6º F is inaccurate. Current average temperatures are even lower, averaging around 97.5º F.

Metabolic Rates are Lower

Researchers explored the potential reasons for this decline in temperature and ruled out improvements in thermometer technology as the cause. Instead, they theorized that human body temperatures have decreased over the past two centuries. This shift was attributed to a decrease in the metabolic rate, which governs energy expenditure. Factors such as improved hygiene, better access to food, higher living standards, and advanced medical treatments have contributed to reduced inflammation in the body, leading to a lower metabolic rate. Additionally, the prevalence of chronic infections in the past, such as tuberculosis, may have driven up body temperatures. The more stable environmental conditions provided by modern amenities like air conditioning and central heating further contribute to a lower metabolic rate. Reduced physical exertion, compared to earlier times, also plays a role in this cooling trend. Dr. Parsonnet highlighted that changes in our living environment, including temperature control, exposure to microorganisms, and dietary habits, have influenced our physiological evolution, challenging the notion of humans as a static species.

How to Find Your Own Baseline Temperature

Body temperature can be influenced by various factors unrelated to health conditions. It is normal for body temperature to naturally fluctuate by up to 0.9 degrees throughout the day, with the lowest readings typically occurring between 3 am and 5 am and the highest between 4 pm and 6 pm. Gender differences also play a role, with men generally having slightly lower body temperatures than women. Women's temperatures can fluctuate significantly during their menstrual cycle. Aging also affects body temperature, with older adults typically having lower temperatures compared to younger individuals. Seasonal variations, obesity, and underlying health conditions can further impact core body temperature. It is crucial for individuals to establish their personal baseline temperature through multiple measurements, as relying solely on the outdated standard of 98.6º F may be misleading.

Where You Take Your Temperature Matters

The location of temperature measurement is crucial. While rectal readings are considered the most accurate, oral and ear measurements are close alternatives, while underarm and forehead readings are less reliable. Individuals monitoring for the health crisis should be aware that temperatures can fluctuate in infected individuals, necessitating multiple measurements throughout the day. A temperature of 100.4º F or higher is classified as a fever. However, older individuals may not always exhibit fever symptoms due to a weakened immune response. Therefore, it is essential to consider other symptoms alongside temperature readings, such as pain, cough, or confusion, when assessing for infection. While body temperature remains a valuable indicator, its interpretation in the context of overall health should be approached with caution, especially for individuals without medical expertise. Extreme deviations from normal body temperature, such as readings above 102º F, should prompt further evaluation. Ambiguous readings around 99º F may require additional monitoring and assessment.

References

Fadó R, Molins A, Rojas R, Casals N. Feeding the Brain: Effect of Nutrients on Cognition, Synaptic Function, and AMPA Receptors. Nutrients. 2022 Oct 5;14(19):4137. doi: 10.3390/nu14194137. PMID: 36235789; PMCID: PMC9572450.

Zhang R, Zhang M, Wang P. The intricate interplay between dietary habits and cognitive function: insights from the gut-brain axis. Front Nutr. 2025 Jan 29;12:1539355. doi: 10.3389/fnut.2025.1539355. PMID: 39944956; PMCID: PMC11813792.

"Food for the Brain" initiative by the Food for the Brain Foundation, a UK-based charity dedicated to raising awareness about the impact of nutrition and lifestyle on mental well-being and cognitive health.

6 Possible Causes of Brain Fog.

5 Causes of Brain Fog, Functional Medicine Meridian ID.

Brain Fog After Eating? These are the Worst Culprits.

How Your Diet Influences Brain Fog.

Brain Fog. Cleveland Clinic.

To Prevent Brain Fog at Work, Watch Wat (And How) You Eat.

Feeling Foggy? Here's How Nutrition Can Help.

Food allergy, intolerance, or sensitivity: What’s the difference, and why does it matter?

Susan Parker

Susan Parker is a 49-year-old Senior Manager at a marketing firm. With two older children becoming more independent, she is now focusing on her own health and wellbeing. She’s passionate about natural and holistic health approaches, and values high-quality, trustworthy products. Susan enjoys yoga, gardening, reading, and cooking, and seeks to stay energetic and sharp while balancing a busy career and personal life.