A recent study defined dehydration and its relationship to pain physiology including both primary and secondary headache disorders.

Evidence does not show improvement in the pain outcomes on Intravenous fluids administration for acute migraine attacks in an emergency department setting. However, increased intravascular volume before diagnostic lumbar puncture may decrease the frequency of post-lumbar puncture headaches from an iatrogenic spinal fluid leak. Keeping euhydration can aid in treating orthostatic and “coat-hanger” headaches due to autonomic disorders. Likewise, preventing fluid losses can mitigate secondary headaches induced by dehydration like cerebral venous thrombosis or pituitary apoplexy.

Thus dehydration alone may provoke headache, but frequently aggravates underlying medical conditions like primary headache disorders or other conditions dependent on fluid balance.

SOURCE- Arca KN, Halker Singh RB. Dehydration and Headache. Curr Pain Headache Rep, 2021; 25. https://doi.org/10.1007/s11916-021-00966-z