Floating weightlessly through space is something many would love to experience. However, for astronauts, in addition to producing both physical and psychological stress, a trip into space affects their core body temperature. A research team from Charité - Universitätsmedizin Berlin have observed that astronauts run hot when exposed to weightlessness. Even at rest, their body temperature is approximately 1°C above the normal value of 37°C. The study findings are published in the journal Scientific Reports.

The researchers found that the astronauts experienced a type of persistent fever; during exercise, the astronauts' body temperature often exceeded 40°C (104°F). The team of researchers, led by Prof. Dr. Hanns-Christian Gunga (Deputy Director of the Institute of Physiology), used forehead sensors to measure the core body temperature (the temperature of the internal body and brain) of astronauts on the International Space Station. The researchers found that the astronauts' core body temperature did not increase suddenly, but that this increase in temperature developed gradually over 2.5 months, eventually reaching approximately 38°C (100.4°F).

"We developed a new technology which combines a skin surface temperature sensor with a heat flux sensor, and which is capable of measuring even minor changes in arterial blood temperature," explains Prof. Gunga. Using this technology, the researchers measured the astronauts' core body temperature before, during and after their stays on the ISS, taking readings both at rest and during exercise. "Under weightless conditions, our bodies find it extremely difficult to eliminate excess heat. The transfer of heat between the body and its environment becomes significantly more challenging in these conditions," explains the space medicine specialist. In space, sweat evaporates more slowly than on Earth, which explains why astronauts were found to overheat particularly quickly during exercise tests performed on the ISS.