Climate changes promise to bring along hotter, longer summers to many places on the planet and the risk of heat-related health problems is also rising.
Most people feel comfortable when the air temperature is between 20°C and 27°C and the relative humidity ranges from 35% to 60%, but when air temperature or humidity is higher, people feel uncomfortable. Such situations do not cause harm as long as the body can adjust and cope with the additional heat. Nevertheless very hot environments can overwhelm the body’s coping mechanisms leading to a variety of serious and possibly fatal conditions.
How heat affects the human body
The sun’s heat radiation is the basis for life on this planet. Nothing would exist without it. Radiant heat from the sun warms your body but, as with everything else, you can have too much of a good thing.
Heat-related illnesses range from minor disorders, like swollen legs or heat rash to the more serious and dangerous conditions of dehydration and heatstroke.
Humans survive in the extreme cold of the polar region and the hot and humid conditions of the equatorial tropics. Despite the climatic variety of the habitats we occupy, our core body temperature remains at approximately 36.90°C.
Even someone acclimatised to the Polar Regions has an average core body temperature only 0.2°C lower than a person living in the tropics. Our insides and our brain do not like to depart much from the average. We can feel stressed as soon as the temperature rises or falls by more than one degree, and feel the need to add or remove clothing, seek shelter, or switch on a heater or cooler. Meanwhile, the body’s own temperature control mechanism goes into action.
Human body temperature control
A tiny gland, the pituitary gland that weighs less than 4g, drives your sex life and also controls your behaviour, the metabolic process, emotions, the involuntary (autonomic) nervous system and the systems that regulate your body temperature.
The gland responds to any rise or drop in body temperature by releasing a particular hormone. This contains instructions for the body to sweat or shiver, contract or expand blood vessels, and increase or decrease the heartbeat and breathing rate. It detects thermal comfort or discomfort and tells you that it is time to escape from the heat or protect from the cold.
How do humans cope with very hot weather?
Human bodies dissipate heat by varying the rate and depth of blood circulation and by losing water through the skin and sweat glands.
The skin handles about 90% of the body’s heat dissipating function.
Sweating, by itself, does nothing to cool the body, unless the water is evaporated. A high relative humidity slows evaporation and in tremendously high temperatures and high humidity the sweat will not dry on the skin. It is not just heat but the combination of heat and humidity that matters; this combination results in the “real feel” temperature.
Heat rash and muscle cramps are early signs that heat is affecting the body. If nothing is done it can lead to more severe situations.
Heat exhaustion is a reaction to severe heat including symptoms such as dizziness, headache and fainting.
Heat stroke is more severe, with dry skin, high body temperature, confusion and sometimes unconsciousness.
A major factor that is responsible for mortality and morbidity is how much the temperature drops in the evening because the body needs a cooler period of time to recover.
A person exposed to heat for a very long time loses the ability to sweat. Perspiration that is dried by the air cools the body, so if perspiration stops the body becomes very hot and a person can rapidly move from heat exhaustion to heat stroke, as the central nervous system and the circulatory system break down.
Does everyone react to heat the same way?
The risk of heat-related illness varies from person to person. A person’s general health influences how well the person adapts to heat and cold.
Extra weight often means trouble in hot situations as the body has difficulty maintaining a good heat balance. Older age, poor general health, and a low level of fitness will make people more susceptible to feeling the extremes of heat.
Medical conditions like heart disease, high blood pressure, respiratory disease and uncontrolled diabetes, skin diseases and rashes may need to take special precautions.
Several substances, either prescription medications or others, can also have an impact on how people react to heat.
Studies comparing the heat tolerances of men and women have concluded that women are less heat tolerant than men.
What are the effects of heat on the body?
When the air temperature or humidity rises above the range for comfort, problems can arise. Exposure to more heat can cause health problems and may affect performance.
In moderately hot environments, the body “goes to work” to get rid of excess heat so it can maintain its normal body temperature. The heart rate increases to pump more blood through outer body parts and skin so that excess heat is lost to the environment, and sweating occurs. These changes place additional demands on the body. Changes in blood flow and excessive sweating reduce a person’s ability to do physical and mental work. Manual work creates additional metabolic heat and adds to the body heat burden. When the environmental temperature rises above 30°C, it may interfere with the performance of mental tasks.
Air conditioning and fans
The number-one factor that minimises heat effect on the human body is access to air conditioning. Fans are totally irrelevant for severe heat as fans do not prevent overheating in really high, hot, hot, temperatures… it actually makes it worse as by blowing hot air on people heats them up rather than cools them down, like a convection oven…
Through history the fact of people dying from heat has always been a reality, but it might be worse in present days, as people are more urban and living to an older age.
Some might like it hot, but extreme heat can severely affect the human body. And the effect is cumulative. It adds up through our lifetime.
Heat kills. Use but do not abuse.
Best healthy wishes,
Dr. Maria Alice
By Dr Maria Alice
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Dr Maria Alice is a consultant in General and Family Medicine. General Manager/Medical Director – Luzdoc International Medical Service / Medilagos. Medical Director – Grupo Hospital Particular do Algarve
