Water is the first-line response when you begin experiencing symptoms of a dehydration headache.

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What causes dehydration headaches can be as simple as not having consumed sufficient fluids. Likewise, dehydration headaches may happen because lack of fluids causes shrinkage in brain volume. This results in the brain pulling away from the skull, which triggers pain receptors in the meninges (the membrane that surrounds the brain). Whatever the mechanisms that might underpin dehydration headaches, scientific evidence can help reassure us that we aren’t imagining them.

• In one study, people who were dehydrated reported headaches as well as difficulty concentrating.

CHRONIC DEHYDRATION?

Do you find yourself feeling perpetually dehydrated? Visit our post Do You Have Chronic Dehydration for an understanding of what causes it and how it harms our health.

• Another study of dehydrated people suffering headaches and other symptoms showed that simply rehydrating helped ease symptoms—and that in some cases completely relieved symptoms.
• Still more research into tension headache causes and migraine causes showed that people who drank six cups of water more than they usually drank during the day reported fewer instances of tension headaches and dehydration migraines along with less severe migraine symptoms.

Dehydration Causes

About 60 percent of your body consists of water, so it’s no surprise that staying well hydrated is vital for many bodily functions. If you don’t drink enough water, your heart, kidneys, digestive system, and cognitive function can suffer.

You’re at risk for dehydration if:

• You’ve exercised vigorously without replacing fluids lost by sweat.
• You have a medical condition that might cause frequent urination (for example, diabetes).
• You take medications that might increase urination (for example, diuretics like hydrochlorothiazide, which is used to treat high blood pressure).
• You deliberately cut back on your fluid intake because excessive urination caused by medications means you are having to get up several times at night to go to the bathroom.
• You have been vomiting due to a foodborne illness such as salmonella.
• You have diarrhea, which limits the amount of water absorbed from food by your digestive tract.

Signs of Dehydration

Your dehydration headache can best be prevented by ensuring that you don’t become dehydrated—but how can you tell if you are? It’s likely that you’ll notice other symptoms as well as your headache. Some common signs that might flag the underlying causes for your dehydration headache include:

• Thirst: This typically sets in if your body loses 1 to 2 percent of its water content (for example, due to perspiration during vigorous exercise). However, keep in mind that if you’re older, you may not feel thirsty even when you are. Dehydration also is a big risk in older people suffering from dementia conditions such as Alzheimer’s disease.
• Fatigue: This occurs because having insufficient fluids in your body causes a drop in your blood volume, meaning your heart has to work harder to pump blood through your circulatory system.
• Dry skin: This is a sign often used by doctors to assess dehydration. Hydrated skin typically snaps down again immediately if pinched. Pinching the skin on the back of your hand is a simple method of checking whether your body had enough fluids.
• Muscle cramps: These can occur if the nerves that feed your muscles are surrounded by too little water.
• Infrequent urination and urinating in smaller amounts: If you’re urinating less than usual, you likely aren’t drinking enough.
• Dark-colored urine: This is a sign that urine is more concentrated than normal due to dehydration. Ideally, urine should be a pale straw color.
• Dizziness: This occurs because of reduced blood volume due to too little fluid in your body.
• Cognitive changes: Studies suggest that dehydration can affect your attention, memory, reasoning abilities, and reaction times as well as cause irritability.

Dehydration Headache Treatment and Prevention

Painkillers such as acetaminophen or ibuprofen can help ease a dehydration headache. But the best way to prevent one is to ensure you drink enough fluids. The Institute of Medicine recommends that women take in about 91 ounces of fluids per day and that men take in about 125 ounces. It doesn’t have to be water only—your fluid intake total can include any other fluids (tea, for example). You also can factor in fluids contained in foods; soup is an obvious example, and some fruits and vegetables are high in water—examples include watermelon, apples, grapefruits, lettuce, and broccoli.

Keep in mind that fluid requirements rise in hot weather, if you’re engaging in physical activity, and if you’re experiencing vomiting and diarrhea due to illness. (See also our post Avoid Heatstroke This Summer.)

If you think you have dehydration symptoms from exercising, take a break and rest until you’ve had time to rehydrate, and if you’re dehydrated due to vomiting and diarrhea, consider replenishing your electrolyte levels. Electrolytes include sodium, potassium, and magnesium, which are present in blood, body tissues, and body fluids. A proper balance is essential for such bodily processes as heart function.

Originally published in 2016, this post is regularly updated.