How hot it is!
When we feel an oppressive heat, our first thought goes to the mercury column of the thermometer. We associate the idea of heat with the idea of high temperatures. In reality our body feels hot also because of the humidity of the air and its immobility. In fact our body defends itself from the overheating provoked by temperatures that are higher than body temperature, by producing sweat, which evaporates on our skin lowering the temperature. Therefore sweating is an important thermoregulating mechanism.
If the air is moving, the hot and humid air surrounding our heated body is moved away and continually replaced by less humid air, and we immediately feel cooler, even though the temperature remains the same. The same happens if the air is very dry, sweat evaporates rapidly and our body cools.
On the contrary, if the relative humidity of the air is high, the sweat on our skin does not evaporate and we feel hot and “sticky”. Our body reacts to this unpleasant feeling producing more sweat in the vain attempt to cool down, and the result is that we soon find ourselves drenched in sweat, overheated and dehydrated. In this way we dangerously draw close to the conditions that provoke the so called “heat stroke”, that takes place when our body is no longer able to control its temperature. If we do not intervene to lower our body temperature, the same rises in an uncontrolled manner provoking severe damages and putting our life at risk.
Briefly, even if our body “functions” better at temperatures below 20°C, we can bear temperatures that are very high (45-50°C) so long as the air is dry, but a feeling of unease arises even at relatively low temperatures if the relative humidity is high.
For example at temperatures between 20 and 30°C with relative humidity around 80% our body experiences a feeling of well-being, while if the humidity increases to 100% we feel a sensation of stuffiness, of malaise and “lack of air”.