Our bodies are constantly trying to cool down. Many of the enzymes that break down our food stop working efficiently if they’re in an environment that is too hot. To make matters more stressful, these reactions are exothermic meaning that they produce heat as a by-product. This vicious circle brings some of the discomfort we feel at high temperatures – signals sent from all over the body telling the brain that there’s a risk of overheating, and that its metabolism is being pushed to breaking point.
The brain responds with, “Get rid of the heat, now!” and blood is shunted towards the surface of the skin. Losing heat on a cool day is easy: the heat from warm blood dissipates quickly from our skin into the air. But shedding heat as the outside temperature approaches our own body temperature (37 degrees Celsius, give or take) is much slower. As another defense mechanism, we start to sweat (and animals that can’t sweat begin to pant), losing heat through evaporation. But if it’s humid as well and hot, the air may already be full of moisture and not able to accept any more from our dripping bodies.
Often, the only option is a drink of cold water, which has the same effect as cooling towers inside a power station, cooling from the inside. A damp towel around the base of the neck also helps, as this is a spot where a huge amount of hot blood flows, and its heat is drawn by conduction into the wet material.
It might be that we’ll all have to become better at shedding excess body heat as the world gets warmer. Heat waves in recent years have led to increased cases of exhaustion and heat-related dehydration – a good argument for carrying a bottle of water and maybe a towel with you wherever you go.
Question from Cameron T Crook via Twitter