Does dehydration cause headache?

A dehydration-related headache may occur with thirst, dry mouth, tiredness, dizziness, darker urine, or reduced urination. It can follow sweating, heat exposure, fever, vomiting, diarrhoea, or a day of limited drinking. The discomfort may ease as fluid balance returns, but headache has many possible triggers, including migraine, infection, poor sleep, eye strain, and missed meals. The presence of a headache alone cannot identify its cause. Consider what happened before it started and whether other symptoms are present.

Move to a cool, quiet place and sip water regularly rather than drinking a large amount quickly. If vomiting or diarrhoea caused fluid loss, an oral rehydration solution can replace water and salts when used according to its instructions. Rest, eat if you have missed meals, and limit heat and strenuous exercise. Do not exceed fluid advice given for a heart or kidney condition. If a usual headache does not settle, a pharmacist or clinician can advise on suitable pain relief and assessment.

Get emergency help for a sudden severe headache, headache after a head injury, confusion, fainting, seizure, stiff neck with fever, new weakness, trouble speaking, vision loss, chest pain, or repeated vomiting. Seek medical advice when headaches recur, steadily worsen, or remain despite rest and rehydration. A clinician can check for dehydration and other causes.

Could fluid loss be contributing to my headache? How much should I drink given my health and medicines? Which warning signs mean I should seek urgent assessment?