During summer, many people notice that the sensation of heat can be more intense than the temperature shown on thermometers. Although the official reading may indicate 34 or 35 degrees Celsius, the atmosphere can seem much more oppressive and stifling. This phenomenon is explained by the concept of "apparent temperature", which describes the difference between the air temperature measured by instruments and how the human body perceives heat.
Apparent temperature is not another measurement of air temperature, but an indicator that describes how the organism feels the surrounding climatic conditions. This factor depends on several elements: air temperature, humidity, wind speed and direct exposure to solar rays. Humidity is one of the most determining factors in this perception, because when the air is very humid, the evaporation of sweat from the skin becomes more difficult. Normally, when temperature rises, the body tries to get rid of excess heat through perspiration, and the evaporation of sweat from the skin helps cool it down.
However, when humidity is high, this evaporation process slows down considerably, and the efficiency of the body's natural cooling system decreases. As a result, the sensation of heat and exhaustion persists even when the actual temperature has not risen significantly. A person may feel on a humid day that the temperature is much higher than what weather bulletins indicate, whereas on another day with the same temperature but lower humidity, the sensation is more comfortable.
Wind also significantly affects the perception of heat. In warm environments, air movement increases the evaporation of sweat from the skin, which can give the body a relative sense of relief. However, warm and dry winds can intensify the loss of body fluids and increase the sensation of thermal stress, especially during prolonged sun exposure or during physical exercise. The speed, direction and nature of winds are important elements when evaluating how a person perceives heat, not just by observing the recorded temperature.
Direct exposure to solar rays plays an equally important role. A person does not feel the same heat standing under direct sunlight as they would in the shade, even if the air temperature is identical in both situations. Solar rays add thermal energy to the body, so the sensation of heat is usually notably higher during midday hours, when the intensity of solar radiation is strongest. This explains the repeated warnings about avoiding direct sun exposure during peak hours.
The perception of heat also varies between individuals, even in the same place and time, due to factors such as age, physical condition, activity level, clothing worn and the degree of acclimatisation to warm weather.
