Normal Body Temperature

For generations, 37°C (98.6°F) has been widely recognised as the standard temperature of the human body. However, scientific research suggests that the average body temperature of people today may be lower than it was in the 19th century. Studies examining historical medical records and modern health data have identified a gradual decline, raising important questions about changes in human physiology, public health and the way doctors interpret temperature readings.

Researchers believe that improvements in healthcare, reduced exposure to chronic infections, changing lifestyles and environmental conditions may help explain the trend. More recently, scientists have also explored whether rising global temperatures could influence how the human body regulates its internal heat. However, the reasons behind the long-term decline are not fully understood, and further research is needed.

Why 37°C May No Longer Tell the Whole Story

The temperature of 37°C became a widely accepted medical reference during the 19th century, following work by German physician Carl Reinhold August Wunderlich. His extensive measurements helped establish a benchmark for identifying normal body temperature and recognising fever.

Modern research, however, shows that human body temperature varies naturally. Age, time of day, physical activity, hormonal changes, the measurement method and individual physiology can all influence a reading. A temperature that is normal for one person may be slightly different for another.

A major study published in the scientific journal eLife in 2020 examined more than 677,000 temperature measurements from three groups of people in the United States. The records covered periods from 1860 to 2017 and allowed researchers to compare measurements collected across different generations.

The researchers found that average body temperature declined by approximately 0.03°C per birth decade. The pattern remained after adjustments for factors such as age, height and weight, suggesting that differences in measurement methods alone were unlikely to explain the entire change.

The findings challenge the idea that every healthy adult should have a body temperature of exactly 37°C. Instead, they suggest that normal temperature may be influenced by changes in population health and physiology over time.

How Better Healthcare Could Be Changing Body Temperature

One leading explanation involves improvements in public health and the decline of chronic infections.

In the 19th century, infectious diseases such as tuberculosis were much more common, while effective antibiotics, modern vaccines and many contemporary treatments were unavailable. Persistent infections and inflammation can increase the body's energy requirements and influence its temperature.

Today, improved sanitation, better dental care, access to medical treatment and reduced exposure to some chronic infections have changed the health conditions experienced by many people.

Researchers behind the 2020 study proposed that these improvements may have contributed to the decline in average temperature. If people experience less persistent inflammation than previous generations, their bodies may require less energy to maintain normal physiological functions.

This explanation is plausible, but it does not mean that lower body temperature is automatically a sign of better health. Modern populations also face conditions such as obesity, diabetes and cardiovascular disease. Body temperature is only one indicator of physiological function and cannot independently determine whether a person is healthy.

Could Modern Lifestyles Also Play a Role?

Changes in everyday living conditions may provide another part of the explanation.

People in earlier centuries often lived and worked in environments with less reliable heating and cooling. Maintaining a stable internal temperature under changing environmental conditions requires the body to expend energy.

Modern homes, workplaces and public buildings frequently have heating, ventilation and air-conditioning systems. These technologies allow many people to spend more time in environments where the body requires less effort to maintain thermal balance.

Changes in physical activity, nutrition, working conditions and access to healthcare may also affect metabolism, which is closely connected to the body's production of heat.

Nevertheless, scientists have not established that any single lifestyle change is responsible for the historical decline. Body temperature is influenced by several interacting biological and environmental factors, making it difficult to isolate one cause.

New Research Examines the Possible Role of Climate Change

A research paper published in Medical Hypotheses in February 2026 proposed that climate change could also influence long-term changes in human body temperature.

The authors suggested that sustained exposure to warmer environmental conditions might affect thermoregulation, the biological process that keeps the body's internal temperature within a suitable range. They discussed whether gradual physiological adaptation to warmer surroundings could contribute to changes in average core body temperature.

The proposal is particularly interesting because global temperatures have risen while studies have documented declining average body temperatures in some populations.

However, the relationship remains uncertain. The 2026 paper presents a hypothesis rather than definitive evidence that climate change is causing the decline. Historical body-temperature studies have also identified other possible explanations, including reduced chronic inflammation and improvements in living conditions.

Researchers need additional long-term studies involving different countries, climates and populations to determine whether environmental warming directly contributes to the observed pattern.

What Does This Mean for Doctors and Patients?

The findings could eventually influence how medical professionals interpret temperature readings, particularly when assessing fever.

A reading below 37°C is not necessarily abnormal. Body temperature changes throughout the day and can differ according to where and how it is measured. Oral, ear, forehead and underarm measurements are not directly interchangeable.

Doctors therefore consider temperature alongside symptoms, medical history, age and other clinical findings. A patient with an infection may need medical attention even without reaching the traditional fever threshold, particularly if other warning signs are present.

Researchers have argued that understanding individual temperature patterns could improve the interpretation of medical measurements. A person's usual baseline may sometimes provide useful context when assessing a possible illness.

However, the emerging evidence does not establish a single new temperature standard that should replace existing clinical judgement. More research is needed before population-level trends can be translated into revised medical guidelines.

Scientists Still Have Important Questions to Answer

Research in Bolivia has also identified a substantial decline in average body temperature among the Tsimane population over a relatively short period. A study published in 2020 examined nearly 18,000 clinical examinations and reported a marked reduction over approximately 16 years.

The researchers discussed possible connections with changes in living conditions, infection, inflammation and other aspects of health. Their findings suggest that temperature trends may occur in populations with very different lifestyles and environments, although the results cannot automatically be generalised to everyone worldwide.

Scientists now need larger international datasets to establish how widespread the trend is and whether it continues at the same rate in modern populations.

For now, the evidence indicates that average human body temperature has declined in several studied populations over time. Improvements in public health and changing living conditions are plausible contributors, while the possible influence of climate change remains under investigation.

The central message is not that humans are becoming dangerously cold. Rather, the research shows that a familiar medical benchmark may not fully capture the complexity of human physiology. Understanding why body temperature changes could help scientists learn more about metabolism, inflammation and long-term health.