Can dehydration cause headaches?

Hi Aya, Yes, dehydration can cause or contribute to headaches.
When your body does not get enough fluids, changes in fluid balance can affect how the brain functions and may trigger a headache. You may also experience thirst, dry mouth, dark-colored urine, dizziness, fatigue, or difficulty concentrating.
As a general guide, many adults need around 2–2.5 liters of fluids per day, although individual needs vary depending on activity, climate, age, pregnancy, and health conditions.
To stay hydrated, keep a water bottle with you, drink regularly throughout the day, and consider using a phone app or reminder alarm to remind you to drink water. You can also make it a habit to drink a glass of water when you wake up, with meals, and before or after physical activity. Aim for pale-yellow urine as a simple sign that you are generally well hydrated.
If you have a medical condition that requires fluid restriction, follow your healthcare professional’s advice instead.