“It’s not the heat, it’s the humidity”, a bit of folk wisdom you undoubtedly have heard countless times from as far back as you can remember. And of course, within limits it’s true.

The human body sheds heat mainly by the evaporation of sweat. It may not be a pleasant sight but a sweat drenched athlete’s body is doing what it evolved to do when the insides heat up. Higher internal temperatures trigger the sweat glands to take action.

When water evaporates a liquid water molecule is launched from your skin into the air surrounding your body – accelerating it into a water vapor molecule zipping through the air. The extra speed requires energy from your skin and each drop of sweat that evaporates takes with it excess heat.

The drier the air, the faster evaporation lakes place (more molecules are launched) and the greater the heat loss. So a heat index of 100° when the temperature is 93° means your body loses heat as if the temperature is 100° not 93°. High humidity hinders heat loss because it slows evaporation.

Heat loss is not the only way high humidity impacts your life – here are four others.

Four Ways Humidity May Affect Your Daily Life?


1. High humidity can accelerate mold growth and some molds release spores when the humidity increases. But most allergenic molds release spores when humidity is low. Do you know why? A dry spore can travel farther than a spore made heavier when moistened by a humid atmosphere. Once the humidity drops there are more mold spores around to make your life miserable because of the accelerated growth.

2. Your hair lengthens as humidity increases. In fact for years most instruments that measure humidity used human hair. A bundle of human hair is linked to a mechanical arm and levers scale up and down motion so it can draw a graph on a rotating drum in the hygrometer.

But there is more to this than than you probably may have imagined.


According to The Atlas of Human Hair Microscopic Characteristics, straight hair generally has a round cross section while curly hair is flatter in cross section. The flatter the cross section the curlier the hair.

So when humidity increases round, straight hair strands lengthen and the effect of the humidity may make your hair go limp and lose body. If you have curly locks, that is strands with a flat cross section, humidity may give you the frizzies as your hair curls even more.


3. Did you ever reach for a potato chip that has been outside for a while on a hot, humid, summer picnic afternoon? You anticipated that satisfying “crunch” but your chips had lost their chomp and instead you reeled back startled by the salty, spongy silence.

Blame the salt! It is what scientists call hygroscopic or water attracting. The sodium and chlorine of table salt carry positive and negative electrical charges while one end of a water molecule is slightly positive and the other slightly negative. Opposites attract and that satisfying salty sprinkle captures humidity, free wheeling water molecules drifting through the space surrounding the chip. The water molecules are then absorbed by the starch of the potato chip. The result is a mealy mouthful.


4. Humidity, also known as water vapor is Earth’s most abundant greenhouse gas. It is important because of its role in the hydrologic cycle, in global warming and locally because it drastically effects night time temperatures.


The High Sierra Deserts of California may drop to near freezing overnight even in summer then soar to 100° the next day. The air can cool drastically at night because of a lack of humidity and a weaker greenhouse effect than in humid regions.

The same factor that makes the dry heat of the day tolerable brings a shiver at sunrise. Earth heat escapes easily to space through an atmosphere that lacks water vapor because of a weak greenhouse effect.

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