how hot is it too hot? This is a very appropriate question now that we do not stop breaking temperature records because of the climate change. If we don’t do anything to fix it, the situation will only get worse and there may come a time when spending time outdoors is really dangerous. Now, where is that point? This is a question that is of great interest to Lewis Halseyprofessor and researcher at the roehampton university, in the United Kingdom. He and his team have spent years trying to find an answer and, although it is not easy to give a concrete number, it seems that it is at some point. between 40ºC and 50ºC.
It all depends on many factors, such as the sex, age or activity of each person. Even so, if the 40ºC barrier is exceeded, the situation becomes dangerous, since the basal metabolic rate. This is a phenomenon that refers to the energy that is consumed per unit of time in a state of rest. The ideal is to keep it as low as possible. In the case of humans, below 40ºC it remains very stable, but when this barrier is passed begins to rise rapidlyespecially when the humidity is also high.
This is where the risks can begin to appear. For this reason, the investigation of Halseywhich has just been presented at a conference on the occasion of the Centenary of the Society for Experimental BiologyIt is something very necessary. And it is that, thus, we can know when it is too hot and take the appropriate measures.
human beings are endothermic animals. This means that we maintain a constant body temperature, independent of the environmental temperature. In our case, it is around 36.5ºC. It doesn’t matter if the street is 10ºC or 39ºC. We always stay at approximately that temperature.
This is achieved through mechanisms such as sweatingwhich is nothing more than the release of a liquid that, once on the surface of the skin, evaporates, extracting heat from the body.
All this also allows us to keep the metabolic rate stable and low, spending as little energy as possible when we are at rest. Unfortunately, everything has a limit. In many animals it has been studied that, if a certain temperature is exceeded, the metabolic rate shoots up, with consequences that affect their health. Interestingly, there are animals in which it has been studied much more than in humans. That’s why, Halsey carried out a study in 2021 aimed at calculating when it is too hot for our species.
The danger of being too hot
During the 2021 study, Halsey and her team put a series of volunteers through four different scenarios, for one hour. In the first, the temperature was 40ºC, with a humidity of 25%. Afterwards, the temperature was maintained, but the humidity rose to the fifty%. Finally, the temperature rose up to 50ºCagain with humidity 25% or 50%.
Thus, it was seen that even in the mildest conditions, with 40ºC and 25% humidity, the resting metabolic rate of the participants rose 35%. Then, at 50ºC with 50% humidity, another 13% was increased. That sudden increase in energy can be seen as a factory at full capacity. The body temperatures of the participants they started to rise too, demonstrating that the usual mechanisms, such as sweating, were no longer enough to maintain a constant temperature. 50ºC is too hot, but even at 40ºC it already there are beginning to be problems.
Our species is not adapted to these increases in temperature, so at this point there could be serious health problems. The sweating would continue to occur, trying to solve the increase in temperature, so the first of those problems is dehydration. It would also increase peripheral blood flow, to try to dissipate heat through the skin. That can cause problems like arrhythmias, syncopes or cramps. Then would come the heatstroke and, if the situation is very serious, even the death.
For all this, it must be very clear that the temperatures that we will begin to see as usual in summer are too hot and can cause serious problems. This should be taken into account especially for people who work outdoors. Heat strokes will become more and more common and, if the population is not adequately warned, there may be many deaths to be regretted. These studies, from now on, will be more and more necessary. Unfortunately, it is something that we must take very seriously.