Can dehydration cause headaches?

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Q. I get occasional headaches. Could it be related to not drinking enough water?

A. Yes, insufficient fluid intake can cause headaches. Some people are much more prone than others to headaches related to dehydration, and people who are more susceptible can avoid the headaches by making sure they drink enough fluids daily. A water-deprivation headache can cause pain throughout the head or be more localized to the front or back. Less often, it is one-sided. The head pain tends to intensify when you bend your head forward or make other head movements. Even walking can make the headache worse.

The exact reason why dehydration causes headaches is unknown. The brain does not have pain receptors. A dehydration headache is possibly triggered by pain receptors in the lining around the brain, called the meninges. When a person is dehydrated, fluid can shift out of the brain, exerting traction on the meninges, which could stimulate the pain receptors. Another possible explanation is the exaggerated response you might feel to any type of pain when you are dehydrated.

A water-deprivation headache should go away within an hour or two after you drink 16 to 32 ounces of water. More prolonged or severe dehydration requires more fluids and lying down for several hours until the pain dissipates. If dehydration is severe and vomiting prevents you from drinking enough to replace the lost fluids, you may need intravenous fluids to relieve the headache. Keep in mind that a migraine attack or any other type of headache can be prolonged if you are not adequately hydrated. Even if you have nausea with a migraine attack, you should try to sip a little fluid every few minutes once your symptoms begin.

— Howard LeWine, M.D.
Editor in Chief, Harvard Men's Health Watch

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