The sweltering heat is one thing. When Mother Nature tacks on that dense layer of moisture that saturates the air, this is when the day becomes uncomfortable. Save for some desert environments around the world, most locations suffer under the discomfort of humidity. Rain forests and tropical climates are more prone to higher levels of humidity, which indicates that high amounts of water have a direct influence on the percentage of humidity.

However, humidity is often simplified as the retention of moisture within the air, and while that’s not wrong, there is a bit of science behind the explanation of this unpleasant phenomenon.

It starts with vapors

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When the concept of humidity is broken down, it can be described as the amount of water vapor in the atmosphere. These vapors are just one of many different gases that make up the air we breathe, caused by the evaporation of water. When water evaporates – say during a period of heat after rainfall – it becomes a moist gas that enters the atmosphere and becomes part of the air that we breathe.

To get to the point where these vapors can be felt, we have to look at vapor pressure and the saturation of vapor pressure. The former refers to the amount of water vapor in the air while the latter is the pressure at which point the vapor begins to turn back into a liquid. The result is a wet air that leaves behind a thin layer of liquid water, or dew. The point at which dew starts to form, or the dew point temperature, is when vapor pressure and saturation vapor pressure are at the same level.

Relative humidity

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In the summer months, when the wrong outfit choice can lead to a soggy, uncomfortable evening, the temperature isn’t the only thing to be concerned about. Relative humidity is the measure of how humid the air is, ranked on a scale from 0 to 100. When relative humidity is at 50%, the air is capable of holding only half the moisture that’s condensing from water vapors. Air that is at 50% relative humidity can leave behind a visible layer of liquid water and can cause clothing to feel damp when exposed for prolonged periods.

Relative humidity is what weather forecasters use when discussing the meteorological conditions as it is the easiest means of conveying how humid the air is. It gives people a frame of reference.

The dangers of humidity

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Being an unavoidable part of nature doesn’t mean that humidity can’t be harmful. Whether too high or too low, the level of humidity can adversely impact those living in such an environment. Humidity that is too low for prolonged periods can cause dry air that, over long periods of exposure, can lead to an increase in the number of cold and flu cases. Dry air may sound comfortable, but it does a number on your insides, specifically by drying out mucous membranes. Without these membranes protecting your respiratory tract, illness is a higher risk.

A constant uptick in humidity can also cause respiratory issues and heart problems. Sweat is a physiological response to heat, but it only kicks in when water that’s already been excreted evaporates. Since it won’t evaporate, the build-up of sweat coats the skin but can’t cool the body, resulting in higher internal temperatures that kick the heart into high gear to try to reduce body temperatures. Areas of high humidity are also known for fungi and mold, which can affect the respiratory systems of even the healthiest individuals.

East vs. West Coast humidity

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By watching the weather or viewing a nation-wide weather map, it’s clear that there is a disconnect between the high humidity of the East Coast and the lower percentage on the West Coast. The primary cause for this has to do with the temperature of the oceans and the prevailing winds.

In the west, the flow of the Pacific Ocean comes from northern waters, which tend to be cooler than the southern waters that flow along the eastern seaboard. Winds on the east also stem from the south, which pulls warm, humid air from around the Gulf of Mexico and the Atlantic. Since the warmer air of the east can retain more moisture than the cooler airs from the north that blow over the Pacific, there will be a higher relative humidity along the East Coast.

The water in the air

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Hopefully, this rundown gave you a better idea of what’s going on during those humid days! Take care of yourself when it’s hot out, and always take the appropriate precautions if you’ll be spending time outdoors.