Causes of Headaches: Dehydration
Excessive exposure to the sun causes headaches in two ways. It gives us headaches by inducing glare and it heats us up, dehydrating us and causing headaches as a result.
The human body is very good at controlling its own internal conditions, keeping the concentration of body fluids more or less the same and maintaining a constant temperature. The way we control our temperature is simple. It takes a lot of heat to change water into water vapour, so at the times when we're hot we sweat, which takes a lot of heat away from the body.
This can occur in one of two situations - when we're working very hard, producing a lot of excess heat as a by-product of muscular movement and also, and most importantly, when we can't become cool because we can't properly evaporate our sweat. This happens when it's very humid. Sweat can't evaporate easily into air that already carries a large amount of water, so it lies unevaporated on the skin, and we become all to quickly aware that we feel hot and sweaty.
Too little fluid in the body — dehydration - can cause headaches in its own right. In addition, sweat contains salt, and a large amount of sweating depletes our salt reserves. This in turn leads to an imbalance of body and blood chemistry, which can make us feel unwell.
Under hot, dry conditions you can lose a lot of fluid, and salt, without knowing. In conditions where the air is dry you won't be able to see that you are sweating.
Although natural weather conditions may not seem dry enough to allow dehydration to occur through insensible sweating (sweating we are not aware of), people in artificially dry environments can lose a lot of water without realising it. Any industrial environment where the air is artificially dried can do this; and because of the laws of physics, simply heating up the air in the room has the effect of relatively drying it out. Warm air can absorb more water than cool air. Therefore hot and/or dry environments may cause dehydration-type headaches; for example operating theatres, hospital wards, foundries, and certain industrial processes taking place in rooms with controlled low humidity.
How do you know if you're dehydrated? Simple. How much urine are you producing? And is it light or dark? If you are dehydrated your body will try to conserve fluid, so the kidneys will excrete very little urine. As a result, the waste products in your urine will be more concentrated, making it a darker yellow colour. On the other hand, (assuming you haven't got diabetes or kidney failure) you're unlikely to be dehydrated if you are going to the toilet several times a day and producing normal amounts of light-coloured urine.
The cure for dehydration is obviously to drink more fluid (preferably non­alcoholic), but do be careful. Drinking copious quantities of water at one sitting isn't good for you and can even be dangerous. Nor is it necessarily just water that you need; sometimes a little extra salt will be necessary to replace some of that lost in the sweat. Wear light clothes, but not synthetics, for sweat can't get out through this material. You're better off wearing, say, cotton or other natural fibres which can breathe. A wide-brimmed sun-hat helps, by keeping the direct heat of the sun off your head and shoulders.
You might think that if you're dehydrated you'd be very thirsty - and you might be - but only up to a point. Its quite possible to feel unwell from salt depletion and dehydration without necessarily being very thirsty.
To prevent dehydration, avoid caffeine and alcohol, which are diuretics. Should you become dehydrated, sachets of rehydrating salts are available from the chemist. Take them with a measured amount of water. In an emergency, you can make a version of this dilute liquid mixture yourself, with one pint of drinking water, one-quarter teaspoon of salt and one tablespoon of sugar. Sip slowly and frequently.
So, too much sun can give you headaches, working through a combination of mechanisms. Excessive sunlight can produce glare, which causes you to screw up your eyes, giving you a tension headache. Excess heat from the sun can dehydrate you and deplete you of salt, both of which can also give you headaches. Often headaches from too much sun are not caused by just one or other of these problems, but by both together. In addition, too much sun is tiring.
If you've had too much sun, go into a cool, less bright environment; perhaps take a cool shower. Drink adequate fluids, use sunglasses, and, if necessary, take a couple of tablets of paracetamol or (where appropriate) aspirin. You may find a short nap helps also. This is probably all that is needed to tide you over what is usually a temporary hiccup in the system.
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