First of all, why do we get headaches? Second of all, why/how can dehydration cause a headache?
In: Biology
some headache pain is still not understood very well, however pain receptors in the muscle, veins, and general tissue in the head and neck are usually what you are feeling. the muscle/tissue on your head has nerve endings, just like anywhere else on your body does, to alert you of potentially damaging actions and effects with a pain response. this pain response is triggered by pressure, temperature, and other factors. inflammation to the head or neck caused by blood pressure issues, swelling, sinus congestion, and much more can trigger these pain receptors.
as for dehydration, this is also actively being studied, but some findings indicate the shrinking of parts of the brain and head as due to retaining less water actually applies a pulling pressure to pain receptors. [https://pubmed.ncbi.nlm.nih.gov/14979888/](https://pubmed.ncbi.nlm.nih.gov/14979888/) A lot of speculation is still being made since headache reactions are difficult to control and test, but typically something is applying force to pain receptors on and around the neck and head, triggering pain response in your brain.
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