Y:        Is it hot in here, or is it just me, Don?

D:        Feels fine to me, Yaël. You don’t have a fever, do you?

Y:        I doubt it. My temperature’s almost always a normal 98.6 degrees Fahrenheit.

D:        98.6 might not be as normal as we think. Scientists noticed that average body temperature in adults has declined since the norm of 98.6 was established almost two centuries ago. One study found that the average body temperature of adults in the UK was 97.9, a study in California found an average body temperature of 97.5, and a study of the Tsimane people, an indigenous population in the Bolivian Amazon, found that their average body temperature was 97.7. One popular hypothesis explaining the drop is that people have been experiencing fewer infections—which raise body temperature— over time thanks to better hygiene, clean water, vaccinations, and medical treatment. Other ideas are that maybe our bodies don’t have to work as hard to fight infections because people are generally healthier, or infections don’t last as long as they did in the past thanks to antibiotics. But those don’t quite explain the decline among the Tsimane people; in rural Bolivia, infections are still pretty widespread. Still another idea is that our bodies don’t have to work as hard to regulate our body temperature because we have access to air conditioning in the summer, and heating, or at least clothes and blankets, in the winter. It’s likely that it’s a combination of these factors.

Y:        So if my temperature is 98.6, I might have a fever?

D:        It’s possible, especially since what’s “normal” varies between people.