Why a Day in the Sun Makes You So Tired, According to Science

There's nothing wrong with a little fun in the sun, but if you're wiped out afterward, that's a red flag.

Nadya-Korobkova/ShutterstockIt’s always fun to plan a weekend getaway somewhere warm or to spend a summer day playing frisbee on the beach (these are the summer activities that burn the most calories, in case you were curious), but ever notice that drowsiness that seems to overtake you after spending a day soaking up the summer sun? There are important reasons you start to feel sleepy after spending hours in the sun—and you shouldn’t ignore those symptoms.

Whether you’re sitting poolside or hiking a mountain trail, the sun is dehydrating your body, the National Sleep Foundation says. Even a relaxing afternoon of catching some rays on your favorite beach towel is causing your body to sweat, losing fluids and salt. The overwhelming sense of fatigue you feel could be a sign of dehydration, and this can increase your risk for other heat-related illnesses such as heat exhaustion. Be mindful of your fluid intake throughout the day and be sure to remain aware of other dehydration symptoms, including stinky breath and irritability. You can also pack along some salty snacks to replace the salts you lose from sweating.

All that extra time in the heat is causing your body to work hard, no matter what kind of fun in the sun you’re having. The National Sleep Foundation explains that our bodies work hard to maintain a constant internal temperature, and when we expose ourselves to long periods of heat, our body has to work in overdrive to maintain that temperature. When you do start to feel overheated, here are some ways to cool down and fast.

As any sunbathing beauty knows, being in the sun results in chemical changes in our body—just take a look at your suntan (or sunburn) for proof and those UV rays can cause serious damage. The same chemicals that cause us to tan can also cause fatigue in the body when we spend too much time in the sun. In order to fight back, The National Sleep Foundation recommends avoiding heading outdoors during the hottest hours of the day, typically between noon and 3 p.m., and taking frequent breaks in the shade. Keep your activity balanced with plenty of resting and don’t forget to pack along a hat or an umbrella for additional cover. If you limit your sun exposure and remain mindful of possible sunburn, you should be able to spend a day outdoors without feeling like you need a nap to recover from it.

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