“It’s not just the heat. It’s the humidity.” That statement is almost a mantra during the summer months, and you may roll your eyes when you hear it for the hundredth time during spin class.
However, there is a lot of truth in it! The humidity doesn’t just make you want a damp cloth; it can also make it much more difficult to cool down on a hot day. Here’s how it all works, plus some tips to beat the heat.
How your body cools you down
On a hot day, your body depends on the surrounding air to help you cool down. You start to sweat when you get hot. As dry air flows over your skin, your sweat evaporates, taking with it some of your body heat. By drawing heat away from your body, air and sweat work together to cool you. This process is called evaporative cooling.
Moist air is full of water particles. In fact, at a relative humidity of 60%, there are 92 grains of water per pound of air. For context, it takes 7,000 grains of water to make one pound.
Evaporative cooling does not work well on a humid day because water does not evaporate easily in high humidity. Your sweat just sticks to your skin. This means your body heat does not evaporate and it is more difficult for you to stay cool.
How does humidity dehydrate you?
It may seem backwards, but it is actually possible to become dehydrated more quickly in wet conditions than in dry conditions. How can that be?
If you start to sweat in a humid environment and still feel warm, your body may try even harder to lower your body temperature. You may sweat more heavily than normal. This process dries you out faster.
If you sweat a lot, you’ll need to drink a lot more water than normal to stay hydrated on a humid day. You also need a larger amount of electrolytes (salt dissolved in water, often mixed with sugar to help you absorb it better) to replenish the electrolytes you lose through sweating.
Hot tips for chilling
Evaporative cooling works extremely well in the desert because the air is so dry. For example, kangaroos in the Australian Outback lick their arms so that the dry air will cool them through evaporation. Luckily, you have more valuable ways to beat the heat! Try these suggestions.
Get acclimatized
Start with short trips outside and acclimate yourself to the heat and humidity, gradually increasing the amount of time you spend outside each day. Eventually, you should start sweating earlier and more heavily than before. Make sure you stay hydrated during this process.
Drink electrolyte drinks
In addition to water, it is important to replenish the salt and sugar that your body loses due to the heat. Store-bought sports drinks often contain large amounts of sugar. Additionally, they come in disposable plastic bottles and can quickly become expensive. You can make your own electrolyte drinks to save money, help the environment and create your favorite flavors.
Avoid the hottest part of the day
Try to limit your outdoor excursions to sunrise and sunset during very hot, humid weather. A nighttime walk under the stars is downright magical in summer!
Wear a cooling vest
Working outside in the heat? A cooling vest could very well save your life. While high-quality cooling vests can be an investment, they keep your body cool by circulating coolant around your torso. Cheaper cooling vests use a series of ice packs to cool you down, but they can still be very effective.
Keep your cool
You’re not imagining it: hot, humid air actually makes it harder to regulate your body temperature by messing up your evaporative cooling system. Fortunately, there are many other ways to stay cool, even on the muggiest of days. Learn the signs of dehydration and heat-related illnesses to stay safe in hot weather. And, as always, keep your water bottle handy.
Author biography
Jane is an environmental writer and founder and editor-in-chief of Milieu.co where she covers sustainability and eco-friendly living.
