Why does being out in the sun make you tired?



Why does being out in the sun make you tired?

In: Biology

For most people, it doesn’t. Indeed some people with seasonal affective disorder find extra sunlight to be invigorating.

There are some people who have suffered demyelinated nerve damage ( MS, ALS, and a handful of other medical conditions ) and who do feel fatigue when exposed to sunlight. The damaged optic nerve simply does not have the bandwidth to handle all the data that the eyeball is trying to transmit. The result is pain, fatigue, and irritability.

If the light is really bright ( like midday in the Sahara desert ) even a healthy person may find that the light makes them fatigued. Again, it is the same issue of bandwidth.

In either case, the connection between inadequate bandwidth and fatigue is not well understood. The best theory that I have heard borrows the concept of ‘crosstalk’ from the field of electronics. IOW, messages ‘jump’ from one nerve to another. This causes unexpected messages in nerves that sense pain, and in nerves that regulate sleep.


EDIT: I see that someone downvoted this post. If you disagree with it, please be good enough to reply and say why you disagree. Being one of those people with one of the aforementioned ‘other medical conditions’, I’d really like to hear if I am mistaken.


Aside from what has already been said, you also have an additional factor in that sunburns effectively are “radiation damage” – i.e, your skin cells taking damage from excessive UV rays. Healing said skin cells can be taxing on the body.

More gentle doses of sunlight, on the other hand, actually are beneficial and even necessary for the synthesis of vitamin D in our skin.

Dehydration may be one aspect. If you’re hydrated, it might be psychosomatic. Remembering working or playing in the sun, and becoming tired? On a normal day you might be actually energetic but talking yourself into being tired prematurely, especially if you aren’t wanting to enjoy outdoor activities.

Behavioral modification and reconditioning may help. Doing activities you enjoy and concentrating periodically on how you’re enjoying the sun.

It is unsafe for your body to get too hot. You heat up when you’re in the sun, but you also heat up if you are being active and moving around exercising.

Some people think that the reason you get tired when you are in the hot sun is that it’s a defense mechanism your body uses to prevent overheating. By becoming tired you are less likely to be over-active and this prevents overheating.

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