We are endotherms (warm-blooded), like other animals and birds, thus our ideal body temperature (about 36.8°C +/- 0.5) is very little affected by the surrounding environment.
At 37 degrees Celsius, our bodies still produce extra heat through metabolic processes. Sweat evaporates from the skin and releases this extra heat into the atmosphere. When the air around us is warm and humid, we lose less heat, thus our internal temperatures rise.
In the same way that a microwave may alter the structure of an egg, heat can alter the structure of proteins in the human body.
The cardiovascular system has to work more than usual when people are exposed to high temperatures. Both the intensity and frequency of contractions need to be increased (your heart rate).
Sweat is easily absorbed by dry air, but not humid air, making the latter more intolerable. Being a muscle itself, the heart requires an increase in blood flow when exerted. However, it can become overworked and eventually fail if the rate at which it pumps blood is greater than the rate at which it receives it. Heat-related heart attacks account for a disproportionate number of reported fatalities during hot weather.
This precariousness is exacerbated by obesity. Insulating the body and providing the heart with a wider network of blood arteries, fat plays a dual role. More heat is generated by the muscles as they work harder to lift and carry the heavier load.
Too much exposure to UV rays can cause DNA damage in skin cells. Repeated sunburns cause DNA damage, which in turn can cause cells to multiply uncontrollably, eventually leading to skin diseases.
Extreme heat has been shown to have severe effects on mental health, and many people report feeling angry on hot days. Substance misuse, mood and anxiety problems, schizophrenia, and dementia were shown to increase on hot days, according to a recent study conducted in New York.
