April 8, 2024/Primary Care

Why Does the Sun Make You Tired? Here Are 7 Reasons

Your body works overtime to keep you cool on hot summer days, bringing on sun fatigue

Man sitting down at beach workout area with head in hand, eye closed

Warm summer days are meant to be spent outdoors. While sunshine can be energizing, spending a lot of time in the sun — even if you’re just sipping iced tea while enjoying the latest beach read — can have you stifling yawns and craving a nap.


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Is it possible the sun is making you tired?

“The heat is more to blame,” says primary care physician Matthew Badgett, MD. “Your body has to work harder to cool you off.”

How active you are while outside and the amount of water you drink also affects your energy.

7 reasons you feel sleepy after being in the sun

Dr. Badgett shares many reasons why the sun makes you tired and discusses what you can do to have more pep when you’re outdoors.

1. Your body is trying to keep cool

Whether it’s cold or hot outside, your body is consistently working to maintain a normal body temperature. When temperatures rise in the summer, sweating is the main way your body cools down. Sweating may seem passive, but your body is hard at work making you sweat.

“Your heart rate and metabolic rate go up when you sweat,” says Dr. Badgett.

Your metabolism uses calories from foods and drinks to fuel body functions like breathing and blood circulation. When you’re hot, your blood vessels expand and send more blood to your skin’s surface.

This process, called vasodilation, allows warm blood to cool down as it travels near your skin’s surface. Vasodilation is also why you may look flushed or red in the face when you’re hot.

2. It’s humid

Heat plus humidity are double energy zappers.

“You feel cooler as sweat droplets evaporate from your skin,” says Dr. Badgett. “But in humid climates, there are already lots of water droplets in the air. The sweat beads evaporate slower, so your heart and body work even harder to cool you down.”


3. You’re not drinking enough

All that sweat dripping off your body is a sign you’re losing a lot of fluids. If you don’t drink enough replacement liquids, you may become dehydrated. Fatigue (tiredness), as well as increased thirst, headaches and fewer pee breaks, are all signs of dehydration.

Dehydration also causes your blood pressure to drop.

“You feel tired because there’s less blood flowing to your brain and organs,” states Dr. Badgett.

4. You’re drinking the wrong beverages

It’s easy to down one, two or more ice-cold hard seltzers or beers on a scorcher of a day. But the mix of alcohol and summer heat can lead to dehydration, fatigue and other dangers.

“Alcohol is a diuretic. It makes you pee more often, so you lose fluids,” explains Dr. Badgett. “You’re also less likely to notice that you’re overheating when you’re drinking alcohol. It’s also a vasodilator so even less blood may be going to your brain.”

5. Your healthy diet is on vacation

Sweetened iced tea, ice cream and salty snacks taste better in the summer. While there’s nothing wrong with an occasional treat, these foods and drinks lack the nutrients your body needs for energy. Instead, you’ll experience rapid spikes and dips in your blood sugar. You may need a nap after that temporary burst of sugar-fueled energy.

6. Your skin is sun damaged

Even when you wear sunscreen, the sun’s powerful ultraviolet (UV) rays still affect your skin. Exposure to morning UV light is energizing and it helps us wake up every morning. But too much sun can lead to sunburn.

“Sunburns raise your body temperature and require energy to heal,” notes Dr. Badgett.

Severely sunburnt skin has a hard time keeping moisture, which affects perspiration and increases your risk of dehydration.

7. You’re in a slump

Many people feel tired after lunchtime — the infamous afternoon slump. This sleepy time coincides with the time of day when the sun is brightest.

“Your natural circadian rhythm makes you tired between 1 and 3 p.m.,” shares Dr. Badgett. “It’s why siestas or naps after lunch are popular in some European and Mediterranean countries.”

Are you tired, or is it heat exhaustion?

While you might feel beat after a day in the sun, sun fatigue isn’t usually a health risk. But heat-induced illnesses like heat exhaustion and heatstroke are.

Heat exhaustion causes extreme fatigue. You also have other symptoms like muscle cramps, nausea and headaches.

“These are signs that your body is working way too hard to cool down and maintain a healthy body temperature,” says Dr. Badgett.

If you don’t cool down soon — by going into an air-conditioned building, taking a cold shower or placing a cool washcloth on your forehead or back of your neck — you may progress to heatstroke.

Also called sunstroke, this serious condition occurs when your body temperature goes above 104 degrees Fahrenheit (40 degrees Celsius). Heatstroke can be life-threatening, putting you at risk for brain damage and organ failure.

Seek immediate medical attention if you or someone you’re with shows signs of heatstroke:

  • Confusion, dizziness or fainting.
  • Fast heart rate and breathing.
  • Nausea and vomiting.
  • Skin that’s dry (no sweat), pale or flushed.


5 steps to stay energized when you’re in the sun

These tips can give you more energy so you can have more fun in the sun:

  1. Fight fatigue with foods that have electrolytes, like watermelon and bananas.
  2. Prevent dehydration by drinking water, electrolyte beverages or a fruit-infused summer drink.
  3. Seek shade under trees, tents and umbrellas.
  4. Take a quick power nap (five to 10 minutes), preferably indoors in air conditioning.
  5. Wear sunscreen to protect against sunburn and lower your risk of skin cancer.

Feeling tired after spending time in the sun isn’t unusual. Still, it’s important to pay attention to your body, especially when working or exercising in the heat. If you notice signs of dehydration or heat illness, seek a cool place to rest and drink more water.


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