So THAT’S Why You Feel So Tired After Being Out In The Sun

Being in the sun is hard work ― or so your brain and body seem to think.

Even when you’re just relaxing on a lawn chair by the pool or at the beach, you may have noticed you feel extra sleepy after being outside in the sun for hours. Why does this happen? 

“The sun causes several changes that result in our bodies needing to work harder, which leads to fatigue,” Dr. Heather D. Rogers, a board-certified dermatologist and founder of Doctor Rogers Skin Care, told HuffPost. 

We talked to doctors about how the sun affects our bodies and why it can make us feel drained — and tips to avoid fatigue and spend time outside safely.

Your body is working hard to regulate its temperature.

“Even if [you] are in a lying position by the pool … your body is constantly working to decrease its temperature to a normal level … when you’re out in the heat,” explained Dr. Patrick Mularoni, pediatric ER physician and medical director of sports medicine at Johns Hopkins All Children’s Hospital.

There are three things your body is doing to try to cool itself down: You’re breathing faster, your heart rate is increasing and you’re sweating more, he explained. These all require extra energy from your body, which can leave you feeling fatigued. 

“In extreme cases when our bodies cannot effectively cool down, people can develop hyperthermia or heat-related injury and illnesses,” said Dr. Shengyi Mao, an internal medicine physician at The Ohio State University Wexner Medical Center. 

Heat exhaustion includes symptoms such as fatigue, dizziness, nausea and headache, according to Mayo Clinic. If heat exhaustion isn’t treated, it can lead to heatstroke, which is the most serious heat-related illness and requires emergency medical care. 

Your body is trying to repair UV damage.

“Too much of the sun’s ultraviolet rays … is very stressful on our skin,” Mao explained. “When we’re exposed to ultraviolet light, our bodies are having to fight off and repair cellular damage, which can result in feeling tired — not only right away but also afterwards.”

What’s exactly happening when sun radiation is damaging skin cells? This causes mutations in the DNA and must be corrected for the cells not to die, Rogers explained.

“The redness of a sunburn comes from blood vessels in that area becoming dilated to bring oxygen and nutrients to damaged skin to help with the repair process,” she said. “The peeling represents dead skin cells that are too damaged to repair.”

Overexposure to UV radiation can also weaken the body’s immune system and the skin’s ability to protect itself from infections, according to the U.S. Environmental Protection Agency. A suppressed immune system leads to more tiredness.

Your body doesn’t have enough water to function properly.

“In the sun, we are losing water faster due to the heat and evaporation so we are more prone to getting dehydrated,” Mao said. “When we are dehydrated, our bodies are working harder to do [their] normal functions, like pumping blood around, which can make us feel tired.”

Drinking alcoholic and caffeinated beverages can further “throw off your water balance” and make you even more dehydrated, Mularoni added. (Additionally, alcohol is a depressant that slows down your brain, causing drowsiness.)

So how do you know if you’re dehydrated? Mularoni recommended looking at the color of your urine when you pee. Light yellow means you are drinking enough fluids, and dark yellow or orange can indicate you are dehydrated.

“If you’re getting to that point where your body is saving all of its water and only sending a little bit of water in the urine, your urine is going to be more concentrated,” he said. “That’s a telltale sign that you’re already behind and you need to be drinking more.”

Your body is releasing built-up stress.

When you’re hanging out by the pool or the beach, this may give you the opportunity to finally slow down and unwind from stress. Your body may recognize that it’s behind on sleep and can finally recover and relax, which can make you feel sleepy, Mularoni said.

What can you do to fend off fatigue and safely spend time in the sun?

None of this is meant to suggest that you stay indoors away from the sun’s rays. In fact, being in the sun can be quite good for you ― if you execute it properly. For example, sun exposure helps your body produce vitamin D, which is key for the immune system and bone health. Also sunshine has been shown to increase serotonin in your brain and boost your mood, according to WebMD.

The problem is when we’re not protecting our skin, not staying hydrated and being exposed to too much sun. “As with anything, too much of a good thing [can be] bad,” Mularoni said.

Here’s some advice on how to enjoy the sun and stay safe, according to experts:

Don’t wait until you’re thirsty to drink water.

While there are recommendations for the number of ounces of water to drink a day, these often need to be higher when you’re spending time in the heat. Mularoni’s rule of thumb for staying hydrated: Drink water before you even feel thirsty. When you do feel thirsty, drink more than you think you should. And remember to hydrate before you get into the sun as well as throughout the time you’re spending outside.

While electrolyte beverages can be useful if you’re exercising or sweating a lot, he said water is best to drink otherwise when you’re out in the sun. Also limit consuming dehydrating beverages, like caffeine and alcohol. 

Protect your skin from sunburn.

Use sunscreen that’s labeled as broad-spectrum (protects against both UVA and UVB radiation) and is SPF 30 or higher, according to the American Academy of Dermatology. When you’re outside, reapply every two hours or after swimming or sweating.

In addition to sunscreen, Mao suggested also wearing protective clothing, sunglasses and hats and avoiding being out in the sun midday.

“Between about 10 a.m and 2 p.m. … the ultraviolet index is high,” she explained. “This is when the sun can do the most damage on our skin and is often the hottest time of day, so this is a great time to take a break in the shade or inside.”

Also Rogers advises not to lie in the sun just for the sake of tanning because it can damage your skin.

“As this damage builds, you speed up the aging of your skin and increase your risk for all types of skin cancer,” she said.

Cool your body off.

Wear lightweight and loose clothing, drink a cold beverage, take a dip in the pool, use a portable fan and seek shade.

“[This] can be very helpful in helping our bodies cool down so we’re using less energy on thermoregulation,” Mao said.

Watch for signs that you need to see a doctor.

The best way to identify if you’re just fatigued or experiencing more serious symptoms of heat exhaustion is to see how you feel once you’re out of the heat. Get into a cool environment and drink lots of liquids. If you’re still feeling ill within 15 minutes, you should seek medical care, Mularoni advised.

If someone seems to be in an altered mental state, such as acting confused or combative, this could be a sign of heatstroke, Mularoni said. Heatstroke can occur if your temperature rises to 104 degrees Fahrenheit or higher and requires emergency treatment to avoid severe complications, according to Mayo Clinic.