Why is 98.6ºF (37ºC) our ‘normal’ body temperature?

Episode #8 of the course “Science questions everyone should know how to answer”

We get a fever when our body temperature rises to fight off bacteria. Even a 1ºC increase in body temperature kills about 6% of fungal species infecting our body. So if this rise in body temperature is helpful for us, why do we not maintain a hotter body temperature? Why do we have such a specific number, 98.6ºF (37ºC), as our normal body temperature?

98.6ºF is the temperature at which we don’t have to eat constantly just to ward off infection. Any higher and we’d have to spend too much of our energy consuming food (calories) just to maintain a higher body temperature. Any lower and we become too susceptible to more bacteria.

Our warm-blooded nature only allows around 100-300 different kind of fungi to infect us. This may sound like a lot, but it’s nothing compared to the 10,000+ different bacteria cold-blooded animals have to deal with. Having a lower body temperature, like when you’re standing outside in cold for a long time, increases the number of fungi that can survive at your body temperature. This is why people get sick more easily after spending a lot of time out in the cold.

Researchers at the Albert Einstein College of Medicine found an optimal point at which both the amount of food we need to consume as well as the amount of bacteria we are susceptible to are both low. That number is 98.1ºF (36.7ºC), very close to the normal body temperature of 98.6ºF (37ºC).

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