Fever vs normal body temperature
Pro Research Analysisby 
Searched over 200M research papers
Normal Body Temperature: Definition, Range, and Individual Variation
Normal body temperature has traditionally been defined as 37.0°C (98.6°F), a value established in the 19th century by Carl Wunderlich and widely used in clinical practice 135789. However, research shows that normal body temperature actually varies between individuals and can fluctuate throughout the day due to factors such as age, gender, activity level, time of day, and even what you have eaten 23579. For most adults, the normal range is considered to be between 36.1°C (97°F) and 37.2°C (99°F), while babies and children may have slightly higher normal temperatures, ranging from 36.6°C (97.9°F) to 38°C (100.4°F) 235.
Recent studies have found that many people have a normal temperature lower than 37.0°C (98.6°F), with average temperatures in some populations closer to 36.1°C (97°F) . Women tend to have slightly higher temperatures than men, and individual temperature is generally stable over time for each person . Because of this variability, experts recommend that body temperature should be assessed in relation to each individual's baseline, rather than relying on a single universal standard 79.
Fever: Definition, Causes, and Clinical Significance
Fever, also known as pyrexia, is generally defined as a body temperature above the normal range. Most sources consider a temperature above 38.0°C (100.4°F) as fever, though some definitions use 38.3°C (101°F) as the cutoff, especially for persistent or unexplained fevers 123468. Fever is a complex physiological response, often triggered by infection, inflammation, or other medical conditions, and is regulated by the hypothalamus in response to pyrogens (fever-inducing substances) 14610.
Fever is not always harmful; it is a sign that the body is fighting off germs or other invaders, and can help the immune system work more effectively 23610. However, very high or prolonged fevers, especially in vulnerable populations like newborns or the elderly, can be dangerous and require medical attention 256.
Hypothermia and Hyperthermia: When Body Temperature Falls Outside the Normal Range
When body temperature drops below the normal range, the condition is called hypothermia. This can occur due to exposure to cold, certain medical conditions, or in frail elderly individuals, and can be life-threatening if not treated promptly 2357. On the other hand, hyperthermia refers to an abnormally high body temperature that is not caused by a change in the hypothalamic set point, such as in heatstroke or drug reactions 45.
Measuring Body Temperature: Methods and Considerations
Body temperature can be measured at various sites, including the mouth, armpit, ear, forehead, and rectum, with rectal measurements being the most accurate . The choice of measurement site and method can affect the reading, and it is important to use the same site consistently for reliable monitoring . Digital thermometers are now commonly used, replacing older mercury thermometers 35.
Clinical Implications: The Need for Personalized Assessment
Given the significant individual variation in normal body temperature, using a single standard value for everyone can lead to misdiagnosis or missed cases of fever, especially in people whose baseline temperature is lower or higher than average 79. Experts suggest that healthcare providers should consider each person's usual temperature when evaluating for fever, and that regular temperature measurements could help establish individual baselines, similar to how blood pressure is monitored 79.
Conclusion
Normal body temperature is not the same for everyone and can vary due to many factors. Fever is generally defined as a temperature above 38.0°C (100.4°F), but what counts as a fever may depend on an individual's normal temperature. Both hypothermia and hyperthermia are dangerous when body temperature falls too low or rises too high. Accurate assessment and personalized evaluation of body temperature are important for effective clinical care.
Sources and full results
Most relevant research papers on this topic