Many individuals find that an indoor temperature of 68°F (20°C) feels surprisingly cold, despite it being a seemingly moderate setting. This common experience highlights that perceived temperature is a complex phenomenon, extending beyond a simple thermostat reading. Our sensation of warmth or cold involves an intricate interplay between our body’s internal mechanisms and various external environmental elements.
How Our Bodies Sense Temperature
The human body maintains a stable internal temperature, typically around 97.7-99.5°F (36.5-37.5°C), through a process called thermoregulation. This precise control is orchestrated by the hypothalamus in the brain, which acts as the body’s thermostat. Specialized thermoreceptors in the skin, internal organs, and hypothalamus constantly monitor temperature changes and send signals to the brain. There are distinct cold thermoreceptors, more numerous in the skin, and warm thermoreceptors, each activated by specific temperature ranges.
Heat is continuously produced within the body as a byproduct of metabolic processes, such as the breakdown of food for energy. When the body needs to cool down, the hypothalamus can initiate responses like increasing blood flow to the skin (vasodilation) and sweating, allowing heat to dissipate through the skin via radiation and evaporation. Conversely, to generate heat, the body can increase metabolism, such as through shivering, or reduce blood flow to the skin (vasoconstriction) to conserve warmth. Individual differences in age, body composition, and metabolic rate can influence how heat is produced and lost, leading to variations in perceived comfort.
Environmental Factors Influencing Comfort
Beyond the air temperature itself, several environmental factors significantly influence how warm or cold a person feels. Humidity plays a role in perceived temperature because it affects the body’s ability to cool itself through sweat evaporation. In low humidity, sweat evaporates more quickly, leading to a greater cooling effect and making cooler temperatures feel even colder. Conversely, high humidity impedes sweat evaporation, making warm temperatures feel hotter.
Air movement, even a subtle breeze, can increase convective heat loss from the body, leading to a sensation known as a “draft.” This increased heat loss makes a room feel colder than its measured air temperature, particularly for individuals who are already feeling cool or are sedentary. The mean radiant temperature (MRT) describes the average temperature of surrounding surfaces and their impact on heat exchange. If walls, windows, or other surfaces are significantly colder than the air, they can draw heat away from the body through radiation, making the environment feel colder.
The Combined Effect: Why 68°F Can Feel Cold
The sensation of cold at 68°F often arises from the cumulative effect of these physiological and environmental factors. At this moderate air temperature, the body is actively working to maintain its core temperature, and even minor imbalances in heat loss can trigger the sensation of cold. For instance, if the indoor air is dry (low humidity), the increased evaporative cooling from the skin can make 68°F feel chillier.
The presence of subtle air currents or drafts, which might be imperceptible in warmer conditions, can significantly increase convective heat loss at 68°F, enhancing the feeling of cold. Cold surfaces like uninsulated windows or exterior walls can radiate heat away from the body, lowering the mean radiant temperature and contributing to discomfort, even if the air temperature is set to 68°F. While 68°F is not objectively “cold” for survival, it represents a point where the interplay of these factors can shift the thermal balance, causing many individuals to feel less comfortable than the thermostat reading might imply.