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Microscope: Sleepy sunshine

By , 12 April 2017

A bouy sleeping in the sunshine, on a green hill.

Time for a snooze in the sun!
Image: ©iStock.com/imagedepotpro

Double Helix magazine is looking for your science questions! Our Microscope column answers the thorniest science queries you can throw at us.

Email us at Helix.Editor@csiro.au or via our contact details below and you could have your question published. Here’s a sample question to get you thinking.

Aisha Goshti asks: Why does the Sun makes you feel sleepy?

There’s nothing like a lazy day at the beach to make you feel sleepy. It turns out that there are several reasons for your sunny snoozing.

One reason is related to temperature. Direct sunlight has a lot of energy, and that can make your body hotter than usual. When you’re hot, you feel tired and sweat a lot – this is called heat exhaustion.

Sweating is great at helping to cool your body. But lots of sweating can cause problems. If you don’t drink enough water, you can become dehydrated, which causes more tiredness, dizziness and headaches. This is dangerous: so remember to drink lots of water when you’re out in the sunshine!

The Sun can also make you sleepy for another reason. When your eyes are exposed to bright light, your body stops making a chemical called melatonin. Melatonin is a hormone that regulates your sleep. It makes sure you’re awake during the day and sleepy at night. When you get out of the sunshine, your body starts producing lots of melatonin. Soon after, you might feel like a nap!

If you have a nagging little query that needs an answer, send it in!

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  1. This article did not quite answer my question, so I’m hoping for an expansion of the answer or an answer that may not have been explored here.

    I’ve often noticed that while driving on a very bright, sunny day that I get an overwhelming urge to sleep. It usually occurs when the sun is high in the sky as opposed to earlier or later hours when it is lower in the sky. Since I carry a lot of extra weight, I am super sensitive to heat, so while I’m in the car my air conditioner is on. My body is not warm or hot when this occurs, but instead I feel quite comfortable temperature wise. In addition, that desire for sleep is occurring in that specific moment – not after I come back indoors. In fact, shade relieves that urge. I feel like the trigger for that overwhelming need to sleep is specific to the light itself, and not just the light, but the “kind” or angle of light. What causes this?

  2. I experience the exact same thing. It really affects me when driving or when I’m out and about in direct sunlight. I immediately feel overwhelmed with lethargy… Almost as if I’ve been tranquilized. It makes me want to sleep right then and there but as you’ve mentioned, shade or a change in environment typically makes it go away. It happens to me often. In fact it happened today when I was driving and I almost pulled over to take a nap ?

  3. Yes Marie, you’ve described what I’m feeling quite well. I’m so glad to hear this is not just me…though I’m sorry you have this same problem.

  4. I also get sleepy when seeing the sun. I have the exact same thing. It’s the sunlight that makes me sleepy. I can fall asleep easier with the sunshine then I can in the dark of night.

  5. Exactly! Why can I stay up all night, while having uncontrollable urges to sleep or nap during the day?

  6. I have the same problem. When I go outside in the bright sunshine even for 1 or 2 minutes I feel sleepy then I take a nap for 10 or 15 minutes then I become ok. I stay all the day in the room. Moreover heat also makes me sleepy like when iam pressing clothes I feel sleepy then I also take a nap for 5 to 10 minutes

  7. Same here.

  8. I have asked doctors this same question and they just say I’m tired. Nope.
    If I go to the beach, I’m guaranteed to be lethargic! It’s really hard to stay awake in full strong sunlight. It may have something to do with Melatonin as I read on another site but it feels like the sun hits my eyes and that’s all it takes to be uncontrollably sleepy!

  9. And I agree! This article doesn’t address the question. It’s speaking of being sleepy AFTER sun exposure. We all want to know about feeling sleepy when we are IN strong sunlight.

  10. Exactly! It’s that powerful drive to go to sleep while in that light, but feeling better once that light is not full strength (shade, indoors…).

  11. I experience the same thing too! When sitting in the passenger seat of a car under shade im completely awake. However once we get into sunlight, i feel sleepy after 30 seconds!

  12. Yes this reasoning also does not explain why sitting in the warm sun in winters makes you sleepy and heavy headed while the hot summer sun has no such effect.

  13. Marie’s explanation perfectly describes my experience. It’s always a struggle taking the long drive to work at about 9am every morning. Once the sun starts to hit my eyes, the uncontrollable sleep sets in within seconds. So bad that music or any distraction can barely stop the sleep.

  14. Ive been told we feel this way, because of our predisposition to be more nocturnal rather than diurnal, basically night owl vs early bird, our body has a natural preference, and we fight it living in modern society. Look it up. Im also a sleepy in the sun person, and shade or going inside

  15. OMG I feel the same as you guys. If you found an interesting answer please notify me!

  16. Okay so I’m not the only one, nice to know. This article and others talk about the general effects of being in the sun, and why it would make you tired, but none of them say anything about why bright sunlight in your eyes would cause you to be sleepy. The only solution that I’ve found has been putting on sunglasses 😎


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