What makes you more uncomfortable? Is It the heat or the humidity? No doubt it’s a combination of the two.
Relative humidity is not a particularly helpful measure of what is comfortable. If the temperature drops, humidity will automatically increase. It could reach 100% yet it does not feel uncomfortable. There can also be stifling hot summer days with aa relative humidity of a mere 40%. On those days, the afternoon heat can soar into the 90s. You would likely be more comfortable in the morning. The relative humidity would be higher yet the temperature would be lower.
Is it the heat or the humidity or is it the dew point?
When you ask is it the heat or the humidity? the role of moisture content is important. A good comfort indicator of comfort is dew point. Water vapor content in the air is reflected with dew point. That water vapor affects people sweating. Sweating naturally cools the body. When the temperature is high the hypothalamus (a gland in our brains) triggers sweat glands to regulate body temperature. Sweat of course, is water. When that water evaporates from out bodies we are cooled. Heat is extracted during the process of evaporation.
If the air is filled with water vapor, it can’t hold much additional water. So when the dew point is high and the water vapor content is high, less perspiration can evaporate into the air. Our bodies can’t cool as effectively. Dew point readings in the 60s indicate moderately uncomfortable weather. When the dew point climbs over 70 degrees, the air becomes very uncomfortable, and as it approaches 80 degrees, it becomes tough to breathe, even for normally healthy people. Of course, when the temperature becomes high, the effect of a high dew point is magnified. The high temperature makes our bodies perspire, and the high dew point works against the natural cooling mechanism.
When there is a high water vapor content in air, it won’t be able to take on more water. So when both the water vapor content and dew point is high and the water vapor content is high, our sweat can’t evaporate into the air. This means our bodies can’t cool down from evaporation.
Weather is somewhat uncomfortable when the dew point is in the 60s. Over 70 and it becomes very uncomfortable. At 80 just taking a breath becomes laboured. The dew point effect is magnified in high temperatures because perspiration is not evaporated.
Hot weather can be dangerous. The rapid loss of salt and water from people’s bodies can lead to heat cramps. Heat exhaustion can follow, causing headaches, nausea, fainting and extreme fatigue. If body temperatures go as high as 106 degrees the body will shut down completely. This is heat stroke. It is potentially fatal.
Is it the heat or the humidity or is it the apparent temperature?
The combination of humidity and temperature is expressed as what the air feels like by the heat index. It is useful in describing comfort levels. An apparent temperature indicates what the air may feel like. The index derives its measure by combining relative humidity (see What is Moisture?) and temperature.
Consider when the heat index, or apparent temperature, is ninety-three degrees. Here we find the relative humidity is 50% and the temperature is 90•. This is very uncomfortable an can have health effects like exhaustion, heat cramps and sunstroke.
Is it the heat or the humidity? Clearly both but you now know a heat index or dew point may be a more helpful comfort guide. You may want to refer to How to Control Humidity to make your home more comfortable.