Why Humidity Makes It Feel Hotter (or Colder!)
May 02, 2025
You've probably noticed that the actual air temperature doesn't always tell the whole story about how hot or cold it feels outside. A 30°C (86°F) day can feel manageable in a dry climate but utterly sweltering in a humid one. This difference is largely due to humidity, and it's why weather reports often include a "feels like" temperature, also known as the apparent temperature.
The Role of Evaporation
Our bodies cool themselves primarily through the evaporation of sweat. When sweat evaporates from our skin, it takes heat with it, thus cooling us down. However, the rate at which sweat can evaporate depends heavily on the amount of moisture already present in the air – the relative humidity.
Relative humidity is the ratio of the current amount of water vapor in the air to the maximum amount of water vapor the air can hold at that specific temperature. When relative humidity is high, the air is already close to saturation, meaning it can't easily absorb more moisture. This significantly slows down the evaporation of sweat from our skin.
Humidity and Heat: The Heat Index
On hot days, high humidity prevents efficient cooling through sweating. Since less sweat evaporates, less heat is removed from the body, making us feel hotter than the actual air temperature. This combined effect of heat and humidity is often quantified by the Heat Index. The Heat Index provides a better measure of how stressful the conditions are for the human body. For example, an air temperature of 32°C (90°F) with 70% relative humidity can feel like 41°C (106°F)! High heat index values indicate a greater risk of heat-related illnesses like heat exhaustion or heatstroke.
Humidity and Cold: Wind Chill (and Dampness)
While humidity's effect is most pronounced in hot weather, it also plays a role in how we perceive cold. On cold days, high humidity can make it feel even colder. This is because moist air conducts heat away from the body more effectively than dry air. Furthermore, if clothing becomes damp in humid cold conditions, its insulating properties are reduced, leading to faster heat loss.
However, the primary factor making cold days feel colder is usually wind, quantified by the Wind Chill index. Wind increases the rate of heat loss from exposed skin. While humidity contributes to the feeling of cold, especially damp cold, wind chill often has a more significant impact on the apparent temperature in winter.
Understanding "Feels Like" on TempTracker
When you check the weather on TempTracker, the "Feels Like" temperature takes these factors into account, providing a more accurate representation of how the current conditions will actually feel to you. It considers air temperature, humidity, and wind speed (though the exact formula can vary) to give you a better sense of comfort or discomfort when heading outdoors.