Here’s the science in a nutshell—or, more accurately, a water balloon. Your brain is roughly 75% water, floating in a cozy cushion of cerebrospinal fluid. When you don’t drink enough, that fluid volume drops, and your brain literally shrinks and pulls away from your skull. Imagine a grape slowly turning into a prune while bouncing around inside a hard shell. Ouch.
That tugging sensation? That’s the meninges—the pain-sensitive tissue wrapping your brain—getting yanked like a rubber band. Studies show that just 1 to 2% dehydration can trigger a headache, and your brain doesn’t have a snooze button. It just whines until you pour water down your throat.
