The origin of 98.6°F as the ideal human temperature

Keeping our body temperature at 98.6 °F

Humans are warm-blooded mammals.One of the features that distinguishes us from cold-blooded species is that we consistently keep our body temperature at approx. 98.6°F – independently of the ambient temperature. Regardless of whether we are an explorer fighting through snow in the Antarctic or trudging through the hot sand of the Saharan desert as a Bedouin: Our body will always try to maintain a consistent body temperature of 98.6°F. And it is well-equipped to do so on account of the heat regulation centers in the hypothalamus (a region in the brain) and the thyroid, which regulates the metabolism and the adrenal glands. The body temperature is kept at approx. 98.6°F – or, strictly speaking, between 98.0°F and 99.15°F – through shivering, sweating, opening and closing the main pores and regulating the blood vessels.



Crawling animals, reptiles and fish are different. These species are cold-blooded and more or less take on or approach the ambient temperature.In any case, they adapt to the outer temperatures. The metabolism of cold-blooded animals is designed to cope with various temperatures.Nature has equipped these creatures with everything they need, allowing them to adjust their metabolism to heat or cold.

As humans we differ from reptiles or other cold-blooded animals.Our body temperature may not deviate from the optimal temperature of 98.6°F by more than 5.4-7.2° for any longer period of time as this would cause death or severely harm us.

Greater deviations from the optimal body temperature are a catastrophe for our organism. Frostbite can cause injuries similar to burns, and extensive exposure to cold is just as destructive to life as an extended fever. Coldness permanently “scars” our body and weakens our organism. Yet even minor deviations of as little as 0,5°-1.0° will cause us to feel unwell, sick and weak.

The ideal body temperature falls within a very narrow temperature window of approx. 1.0°. Our body regulates itself to keep us within this optimal window for as long as possible. While we only notice minor temperature fluctuations in our environment if it exceeds a few degrees – for example a change from 64°F to 71.5°F – our internal temperature sensors are very finely tuned. A temperatures deviation of 0.9° to 1.8° is already experienced as either slightly feverish or hypothermic. Such deviations trigger regulation mechanisms within any healthy and strong organism. Minor deviations from the normal temperature are registered by our heat receptors (thermal receptors), and the body attempts to correct this state as quickly as possible with its heat regulation centers.


Excerpt from the book “Uwe Karstädt: 98.6° F – Ideal Body Temperature

Copyright 2014 |


About Uwe Karstaedt

The German naturopath lives and works in Munich since 1986 and has published many bestselling books on health and alternative medicine. He is an inspiring speaker with a fascinatingly broad range of in depth knowledge about the basic principles of healing on all levels.

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