Does Sleeping With A Fan On At Night Dehydrate You? You Might Want To Keep A Glass Of Water By Your Bed

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It's August, so chances are good that you don't need to be reminded that it's hot and humid. Whenever you go outside, the air is so thick it feels like a warm, wet blanket is wrapped around you. It's pretty miserable! So whenever you're inside, you want to be as cool as humanely possible — and unfortunately, not everyone has access to an air conditioner. If that's the case for you, you're probably leaving a fan on at all times to try and stay as comfortable as you can, even overnight. But is it actually a good idea to do that? Does sleeping with a fan on dehydrate you? The answer might not be exactly what you want to hear.

The truth is that sleeping with a fan on can have some annoying side effects, but not everyone will experience them. According to Sleep Advisor, fans can push around dry air. They can also push and dust and pollen in your room around the air as well, which can be an issue for anyone who is prone to allergies or has asthma.

As for dehydration? According to Live Science, "anything that causes rapid air movement, including a fan, can evaporate moisture from your mouth and nasal passages, drying them out." The constant blast of air on your body can certainly leave you more dehydrated than usual. It can dry out your skin, your eyes (many people sleep with their eyes partially open, even if they don't realize it), and your throat and nasal passages if you're sleeping with your mouth open. It makes sense, when you think about it: having air blast over you for hours at a time is going to dry you out. That's the science behind something like a blow-dryer!

However, this doesn't mean a fan is a terrible option. Dr. Len Horovitz, a pulmonologist at Lenox Hill Hospital in New York City, told Live Science, "There's nothing about a fan that's toxic. There's nothing wrong with circulating air." He also added that sleep is really important, and you may not be able to get that if you're sweating hot all night. So, really, you might need a fan.

There's one more thing to keep in mind, though: back in 2012, a study published in the Cochrane Library found that there is little evidence that shows that fans are actually helpful during a heat wave. When fans pull cool air into the room, they lower body temperature by helping to evaporate sweat. This is great — when the temps are under 95 degrees Fahrenheit. But when they get higher than that, they end up blowing air across your skin that's hotter than your body, and that can make you sweat more. If you're sweating and not replenishing those fluids, you can become dehydrated. And if you're sleeping, you're not replenishing fluids — you're just becoming dehydrated. So basically, if temps are over 95 degrees, you might want to avoid sleeping with a fan on.

You might want to also avoid sleeping with a fan on if you have a lot of allergies or asthma. As stated before, dust and pollen can be blown into your nasal passages with a fan on, which can lead to a cold or a sinus infection.

If you're using a fan and you're worried about dehydration, be sure to keep yourself hydrated throughout the day. You can do this by drinking plenty of water, replenishing with electrolytes in food and drink, and trying to avoid activities that make you sweat profusely.