If We Hear ‘It’s the Humidity’ One More %$#@*& Time!

Sweat is our body's natural cooling system, a unique feature that sets us apart from other mammals. When our body temperature rises, we sweat. However, our sweat is 98°F. So how does 98°F sweat cool us off, and what does humidity have to do with it? Let's break it down. 

Is it reasonable to dump 98°F water all over yourself when you are too hot? That doesn't sound very ingenious to us. But that is what happens when you sweat. This means your sweat doesn't cool you down. If that's true, then why do we think it does?

Ever heard "It's not the Heat, it's the Humidity!" After we sweat, our skin is covered in a thin layer of water. When that energy is transformed from a liquid to a gas (evaporation), evaporation makes the skin cooler.

For example, when the nurse is about to give you a shot, they wipe the skin with alcohol to kill germs. And, like magic, that spot on your skin suddenly feels cold. Alcohol evaporates very quickly, cooling the skin just like sweat does, and that's why it feels cold just before that shot. That is precisely how sweat keeps us from overheating. No evaporation means no cooling! 

For more details on understanding the 5 environmental risk factors for your cooling plan, check out Part 4: Environmental Risk Factors For Heat Stress  in our 7-part blog series about heat education.

Now that we know evaporation is significant in keeping ourselves cool, anything that affects evaporation can help or cause problems as blistering temperatures worldwide keep rising.

Back to humidity! When most people talk about humidity, they are actually talking about relative humidity, defined as the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

Imagine the air like a towel: it can be dry, damp, wet, or completely soaked. Relative humidity measures how wet the air is.

• SOAKED - 100% relative humidity (a completely soaked towel) the air is fully saturated and can't absorb any more water this means 0% evaporation and 0% cooling
• WET - 90% relative humidity (a towel at the end of a pool day) the air is able to absorb 10% more water which means 10% evaporation and 10% cooling
• DAMP - 50% relative humidity (a towel after a few dips in the pool) the air is able to absorb 50% more water which means 50% evaporation and 50% cooling
• DRY - 0% relative humidity (a towel right out of the dryer) the air is able to absorb 100% more water which means 100% evaporation and 100% cooling

When air is 100% humid, (like a completely soaked towel), it’s fully saturated and can’t absorb more water, which means no evaporation or cooling. At 50% humidity, your body can cool effectively, but at 90% humidity, you only get 10% of the cooling effect. This is why 50% humidity feels cooler than 90% humidity.

For example, if it’s 70°F with 100% humidity, there is 0% evaporation even though 70˚F seems cool. This can be very dangerous because the air can’t cool you down and many people have died from heat exhaustion in such conditions. 

For the ultimate cooling experience check out UltraCool with 360-degree cooling. 

The short of the story is to educate yourself on how your body cools itself through evaporation, how evaporation is affected by humidity, and how that affects your situation. This is why it is so important to know if you are buying cooling products that rely on evaporation, like cooling towels, vests, and hats; it may feel good, but if you are in a humid climate they do not give your body any cooling because they will not evaporate just like your sweat and you will get hotter.

At ThermApparel, we use conduction to cool the skin with our PCM cooling packs so they don't need evaporation and work in any climate. Ultimately, look at the humidity levels and let that decide if you need extra cooling today, not just the temperature. We want everyone to be safe and cool.