Not drinking enough water can trigger a headache or migraine in some people. Treatment for dehydration typically involves drinking water to rehydrate. Severe dehydration may need medical treatment.

Little scientific research supports the notion that a lack of water causes headaches. However, the small amount of research available does indicate that dehydration could cause a headache.

There are also cases when dehydration can trigger headaches related to another condition, such as migraine for example.

Keep reading to learn more about the symptoms of dehydration headaches, plus remedies and tips for prevention.

Dehydration happens whenever you lose more water than you’re taking in. Sometimes you may just forget to drink enough water. Most of the time, though, dehydration happens when you exercise vigorously and fail to replenish the water lost through sweat.

On very hot days, especially when it’s hot and humid, you can lose a significant amount of water through sweat. Dehydration is also a common side effect of many prescription and over-the-counter (OTC) medications.

A mild case of dehydration may cause a dehydration headache. Other symptoms can include:

  • thirst
  • dry or sticky mouth
  • not urinating much
  • darker yellow urine
  • cool, dry skin
  • muscle cramps

How does dehydration cause a headache?

There is not a lot of research on headaches associated with dehydration and without another identified cause.

The available research does suggest it is possible to get a headache after a period without drinking, which is quickly relieved by consuming water.

Another option is known as a fasting headache. Many solid foods such as fruit and vegetables contain water, so fasting could also, in theory, induce a dehydration headache.

According to research, a fasting headache can occur 8-16 hours after fasting begins. It usually resolves once a person resumes eating.

A headache related to dehydration can feel different to different people, but the symptoms are typically similar to those of other common headaches.

However, the symptoms of a dehydration headache may also depend on whether there is another underlying cause.

Headache disorders

There are underlying headache conditions that can be worsened by dehydration. For example, dehydration can be a trigger for episodes of migraine or tension headaches.

A tension headache usually causes pain in your head, neck, and sometimes behind your eyes. Migraine is a neurological condition that can cause headache episodes and other symptoms such as nausea or sensitivity to sound and light.

A migraine headache usually affects the forehead or one side of the head. Migraine is typically genetic and can be quite disabling.

Other related causes

Dehydration can trigger or worsen a headache related to other conditions or the effects of substances. For example, you can experience a hangover headache after drinking alcohol. Alcohol can cause dehydration, which can make your headache worse.

A more medical cause is orthostatic hypotension, which is a sudden drop in blood pressure when standing upright.

This condition is often caused by a heart or nerve problem or certain medications. It can lead to what is known as a coat-hanger headache, which affects the back of the head, the neck, and the shoulders.

Another cause can be postural orthostatic tachycardia syndrome (POTS), which is a group of neurological conditions that can trigger migraine and coat-hanger headaches.

If you have symptoms of other underlying conditions, you may wish to speak to your doctor so you can get a diagnosis and appropriate treatment.

Otherwise, if you’re dehydrated and experiencing a headache, you should get some relief by replenishing your fluids.

Drink water

First, get a drink of water as soon as possible. Most dehydration headaches resolve within three hours of drinking. You don’t need to overhydrate: A simple glass or two of water should help in most cases.

Drinking too quickly sometimes makes dehydrated people vomit, so it’s best to take slow, steady sips. You could even suck on a few ice cubes.

Electrolyte drinks

While plain water should do the trick, electrolyte solution drinks help you replenish the minerals your body requires to function.

You get electrolytes from the foods you eat and the things you drink. Dehydration can disrupt the important balance of electrolytes in your body, so replenishing them with a low-sugar sports drink might help you feel better.

OTC pain relievers

If your headache doesn’t improve after drinking water, you can try taking an OTC pain reliever, such as:

  • ibuprofen (Advil, Motrin IB)
  • aspirin (Bufferin)
  • acetaminophen (Tylenol)

Avoid OTC migraine medicines containing caffeine because caffeine can contribute to dehydration.

As always, be sure to check with your doctor before starting any new medications, even OTC drugs. Take these medications as directed with food or water to avoid an upset stomach.

Cold compress

When your head is pounding, ice is your friend. A gel ice pack is generally the most comfortable option. You can usually buy these ice packs with a cover that straps around your forehead. You can also easily make your own.

Many people find that crushed ice cubes make for a homemade ice pack that lies better on their forehead. Put the ice in a plastic bag, place it on your head, and lie down someplace dark and quiet.

You can also try using a washcloth that you’ve soaked in water and placed in the freezer for a bit.

Learn how to make a cold compress.

If you know that dehydration is a headache trigger for you, there are measures you can take to prevent dehydration.

Similarly, if you have an underlying condition that can cause headaches, you can follow these steps to prevent dehydration from making your headache worse:

  • Carry a reusable water bottle in your bag or car so that you have easy access to water when you’re on the go.
  • Avoid sugary drinks. You can add a sugar-free mix to your water to improve the taste.
  • Bring water during your workouts.
  • Avoid or limit caffeine and alcohol

Here you’ll find answers to additional common questions related to dehydration and headaches.

When should a person see a doctor?

While mild dehydration can be treated by replenishing fluids, severe dehydration requires emergency treatment. You should go to the hospital if you notice you are no longer sweating, have low blood pressure, are breathing rapidly, have sunken eyes or shriveled skin, or have dark urine or a rapid heart rate. However, even signs of mild dehydration are enough to take a child or an older person to the hospital.

How do I treat severe dehydration?

You cannot treat severe rehydration yourself. If you are severely dehydrated, you will probably need to be rehydrated using an IV at the emergency room. A doctor will also probably give you an oral rehydration solution to drink. This contains electrolytes and sugar that will help prevent complications. If you have complications such as anemia, your doctor will initiate the appropriate treatment.

How long does it take to rehydrate?

How it takes to rehydrate after dehydration can depend on whether your symptoms are mild or severe. It can also depend on your age, your weight, and whether you have other underlying health conditions.

According to the World Health Organization (WHO), anyone under the age of one will need to receive 30 milliliters per kilogram (mL/kg) of rehydration solution over an hour, followed by 70 mL/kg over five hours. Children and adults over one year need 30 mL/kg for half an hour, followed by 70mL/kg for two and a half hours. You should begin to see improvement after that.

While there isn’t a lot of research on headaches and dehydration, the available research shows that dehydration could lead to a headache.

In addition, it is possible that dehydration may trigger or worsen the symptoms of other underlying conditions that can cause a headache.

In most mild cases, drinking water or over-the-counter electrolyte solution can help rehydrate you and reduce your headache. If you experience more severe symptoms, or if you are an older adult or a caregiver of a child, you should seek emergency treatment.