Why Do People Get Headaches When They Are Dehydrated?

When you're dehydrated, your body doesn't have enough water to keep everything running smoothly. Your brain shrinks slightly because it’s not getting enough fluid, and that can pull on the membranes around it, like a balloon being stretched tight, causing a headache. Think of it like a sponge: if it's dry, it gets smaller, but if it’s wet, it expands.

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Examples

  1. A child forgets to drink water during recess and gets a throbbing head at lunchtime.
  2. An office worker doesn't drink any water all day and starts getting headaches in the afternoon.
  3. After running on a hot track without any water, a runner feels like their brain is pounding inside their skull.

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