Why Does the Sun Make You Tired? (2024)

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The human sleep-wake cycle is hardwired so that exposure to light promotes alertness. However, sometimes people may paradoxically find that they feel tired after being out in the sunshine. Although people commonly feel tired in the sun, the sun is not necessarily always to blame. Multiple factors can cause sleepiness on a sunny day.

We explore the many reasons a summer afternoon might prompt tiredness instead of alertness, as well as tips for fighting fatigue when you feel the urge to sleep on sunny days.

You Are Fighting to Keep Cool

The human body engages in thermoregulation, a process in which it continuously works to maintain a consistent internal temperature of about 98.6 degrees Fahrenheit. Sunny days are often also warm or hot days, and warmer weather requires the body to do more work as it regulates its temperature. For example, you may produce sweat or pump warm blood to the skin to help cool down your core. These efforts use energy.

Overly warm temperatures or strenuous exercise may tax the thermoregulation process and lead to fatigue. In more extreme cases fatigue may be a symptom of heat illness, or hyperthermia, which occurs when the body overheats and cannot properly regulate its temperature.

You Are Dehydrated

The body uses fluids as it cools itself, which means you might need to drink more liquids to avoid dehydration on a warm day. Insufficient fluid intake can force the heart to work harder, and tiredness is a common symptom of dehydration.

A sunny day might seem like the perfect time to go for a run or exercise outdoors, but exercise itself can induce physical and mental fatigue. Sleepiness felt after outdoor exercise in the sun could be more due to the exercise than the sun, or a result of exercising in hot temperatures.

Because exercise heats the body and leads to increased fluid use, exercising in warmer temperatures makes dehydration and trouble with body temperature regulation more likely. Both these processes can prompt tiredness.

Your Immune System Is Activated

Sunlight contains ultraviolet (UV) light, and exposure to this UV radiation can cause sunburn. Results from one older study suggest that regular UV light exposure may contribute to increased mental fatigue.

UV exposure can trigger an immune response as the body tries to protect the skin. In turn, increased immune system activation may contribute to tiredness and the desire for more sleep. More research is needed to confirm, but since sunburn, the immune system, and sleep are interrelated, this may partly explain why being in the sun makes you tired.

You Are Experiencing an Afternoon Slump

Because of the natural human sleep-wake cycle, the time of day when people often feel most tired is in the early afternoon, a period known as the afternoon slump. In many places, the sun is also at its brightest midday and in the afternoon. Sleepiness at this time could be due to the time of day, as well as the other effects associated with warmer weather.

Adopting proactive lifestyle habits may help you feel less tired in the heat.

Stay Hydrated

Drinking plenty of fluids on a warm day helps ward off dehydration and assists the body in cooling itself. In fact, when a person drinks cool liquids, heat transfers into those fluids where it can be released from the body through sweat or urine. Opt for water and avoid alcohol and other diuretics.

Avoid Going Out During the Hottest Parts of the Day

If the heat makes you tired, avoid the worst of it by staying inside during the hottest parts of the day. Avoiding the hottest times is especially important if you are going outside to exercise. Try to time your outdoor activities so you can enjoy the sun during cooler times such as the morning, the late afternoon, or the evening. During heat waves or in places with extremely humid weather, try to seek out air-conditioned spaces.

Take a Short Nap

When sleepiness has more to do with the time of day than the temperature, an afternoon nap might help. A short 10- to 20-minute nap taken during the afternoon slump can increase alertness.

Protect Yourself From the Sun

Loose, long-sleeved shirts and pants, as well as sunscreen reapplied throughout the day, can help protect you from a sunburn.

Know what to look out for so you can act in time to prevent heat illness. Be extra careful in the heat if you are a child, athlete, or older adult. Additionally, you should use caution if you have a pre-existing medical condition or take certain medications.

About The Author

Dr. Michael Breus

Clinical Psychologist, Sleep Medicine Expert

Michael Breus, Ph.D is a Diplomate of the American Board of Sleep Medicine and a Fellow of The American Academy of Sleep Medicine and one of only 168 psychologists to pass the Sleep Medical Specialty Board without going to medical school. He holds a BA in Psychology from Skidmore College, and PhD in Clinical Psychology from The University of Georgia. Dr. Breus has been in private practice as a sleep doctor for nearly 25 years.Dr. Breus is a sought after lecturer and his knowledge is shared daily in major national media worldwide including Today, Dr. Oz, Oprah, and for fourteen years as the sleep expert on WebMD. Dr. Breus is also the bestselling author of The Power of When, The Sleep Doctor’s Diet Plan, Good Night!, and Energize!

  • POSITION: Combination Sleeper
  • TEMPERATURE: Hot Sleeper
  • CHRONOTYPE: Wolf

Why Does the Sun Make You Tired? (2)

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Have questions about sleep? Submit themhere! We use your questions to help us decide topics for articles, videos, and newsletters. We try to answer as many questions as possible. You can also send us an email.Please note, we cannot provide specific medical advice, and always recommend you contact your doctor for any medical matters.

Why Does the Sun Make You Tired? (2024)

FAQs

Why do I feel sleepy after being in the sun? ›

Overly warm temperatures or strenuous exercise may tax the thermoregulation process and lead to fatigue. In more extreme cases fatigue may be a symptom of heat illness, or hyperthermia, which occurs when the body overheats and cannot properly regulate its temperature.

Why does the heat make you tired? ›

Exposure to hot surroundings can jump-start a series of physiological processes in the heart, brain, skin and muscles that can leave you mentally and physically drained. “Fatigue is the body's way of telling us to rest,” says Dr.

How do I stop being tired in the sun? ›

To help prevent heat exhaustion or heatstroke:
  1. drink more cold drinks, especially if you're active or exercising.
  2. wear light-coloured, loose clothing.
  3. avoid the sun between 11am and 3pm.
  4. avoid excess alcohol.
  5. avoid extreme exercise.

Why do we feel sleepy in summer afternoon? ›

Also, the higher temperature of summer makes it harder for the body to maintain a balanced internal temperature. This extra effort can leave you feeling more tired. Feeling tired in summer is so common in many regions, that in countries like Japan, they even have a name for it: Natsubate.

What is a sun hangover? ›

Sun hangover: This condition occurs when you feel under the weather after a day out in the sun.

Do you sleep better after being in the sun? ›

A: Being outdoors for at least some parts of the day can help you sleep better. Get sunlight early, walk outside in the afternoon, reduce blue light at least three hours before bedtime and go to bed in darkness to improve your sleep. Light affects melatonin, a hormone that helps regulate sleep.

Why do sunny days make me sleepy? ›

When it's hot, your body sends fluid and blood to the surface of your body to cool down. This depletes some of your body's resources and can leave you feeling fatigued. To maintain energy, hydrate before, during and after a day in the sun.

Does the sun drain your energy? ›

In the sun the body has to work hard to maintain a comfortable temperature. This increases metabolism (the rate at which you use energy) and can, in turn, contribute to tiredness. This explains why you feel low in energy even if you've just been sitting in the sun all day.

How do you fix heat fatigue? ›

Move the person out of the heat and into a shady or air-conditioned place. Lay the person down and raise the legs and feet slightly. Remove tight or heavy clothing. Have the person sip chilled water, a sports drink containing electrolytes or another nonalcoholic beverage without caffeine.

At what age do you start feeling tired and old? ›

Well, this depends on a person's age, health, fitness level and lifestyle. Generally, the more years that pass, the more you'll value your beauty sleep, and its true senior fatigue is a real thing. However, most people start experiencing a decline in their energy levels by the time they reach their mid-thirties.

Do sunburns turn into tans? ›

Not all sunburns evolve into tans. "After the skin heals from a sunburn, the affected area may become more tan than surrounding areas," DeRosa explains. However, she notes that "this is not a good thing, as tanned skin is also a sign of skin damage caused by the sun.

Why do I feel lazy in the sun? ›

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.

Why do I feel so weak in hot weather? ›

Dehydration. Low energy and tiredness are also common when you're lacking hydration. “Hot weather increases the rate of fluid loss through sweating, leading to dehydration. Dehydration can contribute to fatigue and make you feel even more lethargic,” adds Dr Shah.

Should I go back to sleep if I wake up tired? ›

Should I go back to sleep if I wake up tired? If you wake up tired occasionally, it might just be a one-off poor night's sleep, so a little extra snooze could help. But if this is a recurring issue, it's essential to investigate the underlying causes rather than just trying to sleep more.

Why do I sleep better after the sun comes up? ›

The connection between vitamin D and melatonin

The interlaced functionality of vitamin D and melatonin are clear. The sun is the most optimal way of improving the levels naturally. Vitamin D is involved in the pathways of melatonin and is directly involved in several enzyme expressions in the brain related to sleep.

Can bright light make you sleepy? ›

Your body's circadian clock responds to light, as a signal to be awake, and dark, as a signal to fall asleep. Increase your amount of light during the day to be more alert. Darken your bedroom room at night to sleep better. Avoiding bright light 2 hours before bedtime will make it easier to fall asleep.

Can too much sun keep you awake? ›

Sunlight exposure impacts how much melatonin your brain produces, which is what tells your brain it's time to sleep. When it gets dark, you start producing melatonin, so you're ready to sleep in about two hours. With more sunlight in the summer, you're likely to feel more awake.

Why does laying in the sun feel good? ›

Exposure to sunlight is thought to increase the brain's release of a hormone called serotonin. Serotonin is associated with boosting mood and helping a person feel calm and focused. At night, darker lighting triggers the brain to make another hormone called melatonin. This hormone is responsible for helping you sleep.

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