A dehydration headache is head pain that comes from running short of fluid, and for most people the fix is ordinary: drink, rest, and give it a little time. Harvard Health says it should go away within an hour or two after you drink 16 to 32 ounces of water. Cleveland Clinic says it usually lasts a few hours. If the pain is still there a few hours after you have had water and a break, see a healthcare provider.
That timeline is also the most useful test you have. A headache that follows it was probably about fluid. A headache that does not, or one that arrives with the warning signs listed further down, is telling you something else.
Why a dehydration headache happens
Nobody has fully settled why losing fluid makes your head hurt. Harvard Health says the exact reason is unknown. One explanation is mechanical: as you lose fluid, the brain and other tissues shrink slightly, and Cleveland Clinic describes the brain pulling away from the skull and pressing on the nerves around it. Harvard Health points to the meninges, the lining around the brain, which carries pain receptors that the brain itself lacks. It also suggests that being dehydrated may make you react more strongly to pain of any kind.
Whatever the exact mechanism, the pain eases when the fluid comes back: when you drink, the brain returns to its usual size and the pain goes away.
What it feels like, and how to tell it is dehydration
There is no single location. You may feel it all over your head or in one spot, at the back, front or side. It is usually a dull ache, but it can be sharp, stabbing or throbbing. It tends to get worse when you bend over or move your head, and Harvard Health adds that even walking can make it worse.
Because so many headaches feel alike, Cleveland Clinic gives three practical checks for a dehydration headache:
- It goes away or improves after you drink water and rest.
- The pain is only in your head. Other types of headache can also hurt in the neck or shoulders.
- You have other signs of dehydration, such as darker pee than usual, a dry mouth or tiredness.
A dehydration headache can also make a migraine more likely, and Harvard Health says a migraine attack can last longer when you are not drinking enough. Headaches that keep coming back are worth a conversation with a provider, since repeated headaches can be a sign of long-term dehydration.
What causes the fluid deficit
You took in too little, you lost more than you replaced, or both. MedlinePlus lists the usual losses: heavy sweating, fever, vomiting, diarrhea, and some medicines that make you urinate more. It also lists the reasons people drink too little, including feeling too sick to eat or drink.
Las Vegas makes both easy. A day outdoors in summer heat raises sweat losses, and during some activities you may not notice how much you are sweating. Thirst is not a reliable alarm either: some people with dehydration do not feel thirsty at all. Alcohol and caffeine add to the problem, since both are diuretics that make you pee more.
How to clear it
Cleveland Clinic calls rehydration the fastest way to treat a dehydration headache.
Sip, do not gulp. Drinking a lot of water very quickly can make you feel sick to your stomach. If your stomach is unsettled, try sucking on ice cubes.
Replace electrolytes if you have been sweating. After heavy sweating, a low-sugar sports drink replaces the electrolytes you lost. MedlinePlus warns against salt tablets, which can cause serious complications.
Rest somewhere cool. Stop the activity that got you here. If you are in the sun or heat, move to a cool, shady place. An ice pack wrapped in a thin towel, or a cold washcloth on your forehead, can also help.
Pain relievers help, but they are not the treatment. Over-the-counter NSAIDs can ease the pain and may help you feel better sooner, but only fluid treats the dehydration that caused it.
A bigger deficit takes longer. Harvard Health says more prolonged or severe dehydration needs more fluid and several hours lying down, and AFC Urgent Care notes the headache can last into the following day when dehydration is more severe.
Where an IV fits, and where it does not
An IV puts fluid straight into a vein, so it bypasses digestion entirely. None of the medical sources cited here compares the two routes for a headache, and none says an IV clears it faster than drinking. If you can drink and keep it down, drinking is the treatment.
In the sources, IV fluids belong to severe dehydration. Cleveland Clinic says a provider may give IV fluids if dehydration is severe. MedlinePlus says severe dehydration may need a hospital stay with fluid through a vein. Harvard Health says IV fluids may be needed when severe dehydration comes with vomiting that stops you drinking enough. With a headache, those same situations are reasons to go to the ER, which is why we do not suggest a home drip for a dehydration headache that comes with nausea or vomiting, or with any of the other signs in the next section.
Our home IV is a choice for convenience, not a faster cure. If you are not nauseated or vomiting, and have none of the signs in the next section, including a headache that has not eased a few hours after water and rest or one that keeps coming back, and you would rather have fluid given at home, our IV Fluids treatment is an option. It is hydration only, given after a health check.
When to get medical care
Most dehydration headaches go away at home. These are the signs that one needs more.
Go to an emergency room if you have a headache along with any of these. Cleveland Clinic lists them as symptoms of severe dehydration:
- Nausea and vomiting
- Dizziness
- Confusion
- Passing out or fainting
- A heart rate faster than 120 beats per minute at rest (adults)
- Vision problems
Call 911 if someone loses consciousness, becomes confused or has a seizure, has a fever over 102°F, shows signs of heatstroke such as a rapid pulse or rapid breathing, or gets worse despite treatment. Those are among MedlinePlus's reasons to call 911, and it describes severe dehydration as a life-threatening emergency.
See a healthcare provider if:
- The pain lasts more than a few hours after you have had water and a break.
- The headache keeps coming back, or you cannot manage it at home.
- You are an older adult or have a long-term condition such as diabetes, which MedlinePlus says raises the risk of dehydration, and you are not sure how to manage fluids.
For a child, see a healthcare provider right away if a baby or child has a headache along with other signs of dehydration, such as pale skin or fewer wet diapers.
Common questions
Sources and References
- Cleveland Clinic. Dehydration Headache: What It Is, Symptoms and Treatment. https://my.clevelandclinic.org/health/diseases/21517-dehydration-headache
- Harvard Health Publishing. Can dehydration cause headaches? https://www.health.harvard.edu/diseases-and-conditions/can-dehydration-cause-headaches
- MedlinePlus, National Library of Medicine. Dehydration. https://medlineplus.gov/ency/article/000982.htm
- AFC Urgent Care. How Long Does a Dehydration-Related Headache Last? https://www.afcurgentcare.com/elizabeth/blog/how-long-does-a-dehydration-related-headache-last/
