Three Reasons That the Sun Makes You Tired

This content was created by the National Sleep Foundation

Is the sun sapping your energy? How to fight back

If you’ve ever felt drained and exhausted after spending a day at the beach, it’s not a fluke. Long hours of sun exposure really can make you tired—but it’s probably not for the reasons that you think. For one thing, it doesn’t mean that you’ve overdosed on vitamin D. But it could mean that the following factors have set you up to feel tired.

1. Your Body Is Trying to Control Its Temperature.

Normally, your body works hard to maintain a consistent internal temperature. But when you’re exposed to direct heat while spending time in the sun, your body ends up working overtime to keep you cool. Your heart rate and metabolic rate can increase, too. All this extra physiological effort can make you feel tired or sleepy, even if you’ve just been sitting in the sun.

2. You're Dehydrated.

Even if you’re not engaged in strenuous physical activity, spending time in the sun can quickly dehydrate you. This is partly because your body is working hard to stay cool and partly because you may be losing fluids and salts through sweating. Fatigue is one of the primary symptoms of dehydration, which can increase your risk of heat exhaustion.

3. Your Body Is Experiencing Chemical Changes.

It’s no secret that the sun’s ultraviolet rays can penetrate the skin and cause damage (such as sunburn, pigmentation changes, and wrinkles). The cascade of chemical changes that produce these effects can also cause fatigue after hours in the sun.

To prevent sun-induced fatigue from setting in, avoid spending extended periods of time in direct sunlight during the day’s hottest hours and seek shade whenever possible. Sip plenty of water while you’re outside, and consider having a salty snack (like pretzels or baked potato chips) to replace the salts you’ll lose while sweating—but drink plenty of fluids, too. Try to strike a balance between being active and resting. It also helps to wear a hat or sit under an umbrella to reduce the amount of direct sunlight that’s on you.