Why does sunlight make me tired?

Heat from the sun dries you out causing you to become dehydrated and it will give you usually an overdose of vitamin D if your there in the sun too long so i would assume with the combination of the two and you being dehydrated your body slows down. so you may become tired ....

I also have this occur. Although, admittedly, I have never deemed it a problem. I quite like falling asleep in the sun, though I suppose it's dangerous to drive on sunny days.

Anyhow, as a person in a medical field, I believe that becoming tired in sunlight is a stress response. Or lack thereof, rather. When we are cold, focused, or stressed about life our bodies increase the amount of cortisol in our bloodstream. This is a huge problem because it can cause a number of health risks and it slows down the body's immune response, etc. What happens when sunlight penetrates the skin, warms us up, and creates "happy" feelings is a certain amount of chemicals are released into the bloodstream creating stress relief and genuine, physiological happiness which, in turn, fatigues us. Consider it an immune response for it is in a state of rest that the body heals.

I first found out I had a sun allergy in at a vacation in Hawaii. All the previous doctor visits I had made due to my red, puffy face I attributed to poison oak exposure. My doctor just took one look at me and agreed with me...then in Hawaii, the doctor there said, "No, you have sun sensitivity, I see it all the time here." Then when I made an appointment with the dermatologist they said the same thing..Sun lotion blockers do not work, my skin first gets red, i get exhausted, like I had chemo therapy, and i just sleep to get over it. Even driving for an hour in my car affects me tired wise and my face and neck, exposed in the car, get red and I get a nasty rash that takes weeks to go away. I don't get much help from doctors...they said, Put a fan in front of your face when you drive, stuff like that, so we are on our own on the internet searching for solutions.

Because there are powerful rays in the sun that absorb energy and vitamins from all sorts of things, even humans from their body or maybe you have sensitivity to strong light, like if you wear glasses or cap something like that it will help you from heavy sunlight. All of those things can relate to the sun making you tired.

I have a similiar problem and the doctors always tell me on blood test that I have dangerously low vitamin d even though I have taken supplements. The last time was just when I spent a full week outside painting my house and then went in for the test and was taking supplements. Wondering if my body over uses vit d. I am not a pale person and normally have a tan but if I spend longer than an hour outside, I normally end up physically ill from the sunlight which means headache, vomiting, and freezing. I constantly feel tired during the day then at around 7 pm I get tons 0f energy and want to get everything done, I'm also more productive during the winter when less sun. My husband thinks I have a sun allergy. Wondering if that could be true and this it the varying reactions we're getting.

You should look into the subject of Porphyria, and particularly acute intermittent porphyria. Although considered a rare disease, the gene defect is carried by many people without serious symptoms. Anything that stresses the body causes toxic build up of ALA and Porphobilinogen and sun is known to be a common stressor in this way.

The weight applied to your chest by the heavy barometric pressure which usually comes with clear weather may have something to do with it.

You wrote the exact post I was going to write. Also I have to pull over and take a nap for 15 min every now and then when driving an hour or more just on sunny days. My doctor has never heard of any such condition, but said he will look for info.

It is huge problem because of this slow down our health immune system.In sunny days because of overdose of vitamin D, and also the dehydration takes place i.e body loos the water in the form of steam and the body become tired.
In summer season we need more mount of to drink.

'Solar urticaria' can be a reason. I have this so I break out in a rash if I'm in direct sunlight for a long while too. The sun makes me drained and tired and I have to sleep if I'm in strong sunlight for even 20 mins.
Apparently the body gets drained as it's is making antibodies as a result of the cells changing to deal with UV light.
http://en.wikipedia.org/wiki/Solar_urticaria

After a long winter in Michigan USA), when I stepped off the plane in Orlando, Florida, I felt like a million bucks. The snn and bright light was a blessing.

yes this is true...vitamin D.

You may be allergic to the sun, have your histamine levels checked as well as IgE and IgG (immunoglobulins) while you are in the tired state. If they are high, you are allergic / sensitive to the sun the same as in the case of Michael Jackson (Vitiligo) minus the skin discoloring. You may notice a puffy face or other markers of inflammation in the body. Try regular Claritin and see if the tiredness goes away and then you have your answer. You can also take Quercetin from your local health food store. It's a natural mast cell stabilizer, the antihistamine drug Nalcrom is derived from it.

I also feel fatigued and "icky" in direct sunlight, no matter if I feel hot or not. The thing is I'm not a night owl, I actually prefer daytime activities just when it is cloudy or in the shade. I have had a few rashes that may be caused by photosensitivity but that is rarer and might be something else. I have also always wondered what it was.

Omg I am so happy to find this forum.i have a doctors appointment tomorrow morning
I thought I've been going nuts! I'm 35 and all my life I the sun drains me. I live the winter months bc there is barely sun. I feel so unproductive bc of this issue. I've been tested for thyroid, blood pressure, diabetes, iron, sleep apneia, and all normal. I see my sister go out and play and I too, was made to go out but I immediately found shade and just sat there. At night I'm alive, go outside, I'm up until 4am..it's like I can function normally.
I used to have to get up for work at 5 am and it was so easy bc the sun wasn't up yet..

Energy from the sun transfers heat to the body and causes our body temperature to increase.When our body temperature changes more than .5 degrees, our body reacts by being tired.When we are out in the sun, our body has to work hard to regulate our body temperature,our heart rate and metabolic systems increases.That invisible work makes us feel exhausted.

I haven't read through the entire thread, but did anyone suggest being a vampire? I expect the sun would wear you right out.

As a few have pointed out, it's Vitamin D. I might be able to relate to this because I've had periods where a calcium deficiency was obvious. Although that's not the reason to feel tired. It is just when you are out in the sun, your body kind of gets overheated and wants to chill out. Nothing to worry. A visit to the doctor wouldn't hurt either though.

Save for later.

I too have noticed a depletion of energy when I've been in the sunlight a long time, and it's especially serious if I get a sunburn. It may simply be that the body is using energy to try to cool the surface of the skin. Even on a relatively cool day of say 70 or 80 degrees the the direct rays of the sun greatly increases the temperature of the skin. Over a long period of time this could take a lot of energy. The same energy drain occurs on a hot day even in the shade because the body is trying to keep cool by sweating.