What Is Dehydration?

A man working outside sweats and drinks from a bottle of water

Ned / Getty Images

Dehydration occurs when your body loses more fluids than it takes in. It is a common problem that can affect someone of any age, but dehydration is particularly prevalent among older adults. In fact, it's estimated between 17% and 28% of all older adults in the U.S. experience dehydration. Infants and young children are also at increased risk, as are other populations based on medical, lifestyle, and environmental factors.

There are several types of dehydration which largely depend on whether water and sodium are lost from the body at the same time or at different rates. If you are dehydrated, you likely feel extremely thirsty and may also be fatigued and have dark urine. Dehydration can become serious, with the condition being a common cause of hospital admission. Before it gets to that point, dehydration is oftentimes treatable—and preventable—with fluid intake.

Types of Dehydration

There are three primary forms of dehydration. Because the characteristics and causes of the types differ, healthcare providers will determine which type of dehydration you are experiencing and tailor your treatment accordingly. Here is a closer look at each type of dehydration:

  • Isotonic dehydration: This type of dehydration occurs when you lose water and sodium together. Typically, this results from vomiting, diarrhea, sweating, and burns. Kidney disease, high blood sugar (hyperglycemia), and Addison's disease can also lead to isotonic dehydration.
  • Hypertonic dehydration: When your water losses exceed your sodium losses, you have hypertonic dehydration. Fever, increased breathing, and diabetes insipidus (a rare condition that causes you too produce too much urine) can lead to hypertonic dehydration.
  • Hypotonic dehydration: This type of dehydration is mostly the result of diuretics, or water pills. When hypotonic dehydration occurs, you lose more sodium than water.

Dehydration Symptoms

The severity of your dehydration will play a role in your symptoms. Most people who are dehydrated are thirsty. Other signs and symptoms of dehydration include:

  • Fatigue
  • Dry skin and lips
  • Dark urine or decreased urine output
  • Headaches
  • Muscle cramps
  • Lightheadedness
  • Dizziness

Signs of significant dehydration include:

Many times, dehydration is mild. Sometimes it can become severe enough that it is life-threatening. Signs that you should get immediate medical attention include:

  • Fainting
  • Heart palpitations or rapid heartbeat
  • Confusion
  • Lack of urination
  • Rapid breathing

In infants and young children, signs and symptoms of dehydration can be:

  • Dry mouth and tongue
  • No tear production when crying
  • No wet diapers for at least three hours
  • High fever
  • Unusual sleepiness
  • Irritability
  • Eyes that look sunken

What Causes Dehydration?

Water helps your body perform a variety of functions. For instance, water plays a part in regulating your temperature, lubricating joints, and removing waste from your body. As you sweat, urinate, and make bowel movements, water leaves your body.

So that your body can continue to function properly, you need to replace the water you lose. If you are not taking in enough fluid—whether that's through water or another type of beverage—to replenish your lost water, you can become dehydrated.

Risks of Dehydration

There are a number of factors that can increase your risk of dehydration, including:

  • Intense exercise
  • Hot climates, particularly if you are exercising or working
  • Certain medications
  • Illness
  • Fever
  • Lack of access to water
  • Medical conditions, such as those that lead to increased urination or sweat

The most common reasons people get dehydrated are diarrhea, sweating, and vomiting. Because they more often vomit and have diarrhea, infants and young children are particularly at risk for dehydration.

Older adults are also at higher risk for dehydration because, as people age, they can lose their sense of thirst, so they don't drink enough fluids.

You're at risk of dehydration if you don't take in enough fluids. You're less likely to drink enough if you:

  • Are sick
  • Are nauseous
  • Have a sore throat or mouth sores

How Is Dehydration Diagnosed?

There's no one definitive way to test for dehydration. Instead, healthcare providers often use a variety of approaches to diagnose dehydration. In addition to doing a physical exam and checking your vital signs, providers might also order blood tests and urine tests. Here are some of the tests a healthcare provider might use to diagnose dehydration:

  • Electrolyte test: A healthcare provider may order blood tests to check your electrolyte levels, especially your potassium and sodium levels. These minerals help balance the fluids in your body. When they are not at appropriate levels, you can become dehydrated.
  • Kidney function test: Sometimes a healthcare provider will order blood tests to check your kidney function. Your kidneys play an important role in removing water and waste from your body, but if they are not functioning properly, you can become dehydrated.
  • Urine test: The level of sodium—as well as other markers—in your urine can be help healthcare providers determine if you are dehydrated.
  • Weight measurement: When available, healthcare providers can compare your previous weight to your current weight to identify dehydration. Typically, a weight loss of 3% or more over seven days may indicate dehydration.

The healthcare provider will also likely ask you about whether you have been engaging in anything that increases your risk of dehydrations, such as staying in the heat or heavily exercising.

Treatments for Dehydration

Your treatment for dehydration will vary depending on the severity of your condition and the underlying cause.

For those with mild dehydration, you can replenish lost fluids by consuming water. To make it easier—especially if you are vomiting and have a hard time keeping down drinks—try sipping water or sucking on ice cubes.

If blood tests show your electrolytes are low, you can drink a sports drink. For children who are dehydrated, there are special rehydration solutions available in stores.

If your dehydration is severe, you may need to have your fluids replenished with a intravenous at the hospital.

How to Prevent Dehydration

The best way to prevent dehydration is to ensure you are drinking plenty of water—or other beverage—each day. Experts generally recommend drinking approximately nine cups of fluid each day if you are a woman and 13 cups per day if you are a man. That said, your exact needs will vary based on your age, medical conditions, and activity level.

If you regularly work in high heat, it's recommended that you drink 8 ounces (oz) of water every 15 to 20 minutes. Drinking in short bursts is more efficient and safer than drinking large amounts less frequently. To prevent any potential side effects of drinking too much water, avoid drinking more than 48 oz in an hour.

You should also drink extra fluids when you are sick. You shouldn't wait until you are dehydrated to drink fluids—drink extra if you have a fever, are vomiting, or have diarrhea.

Related Conditions

Sometimes dehydration is a side effect of a health condition. Here are some conditions that tend to increase the likelihood of dehydration. If you have one of these conditions, it is important to ask a healthcare provider for tips on how to stay hydrated.

  • Swallowing difficulties: People with dysphagia, or difficulty swallowing, are more prone to dehydration. In fact, the prevalence of dehydration in people with dysphagia ranges anywhere from 44% to 75%.
  • Diabetes: People with diabetes are more prone to dehydration—especially when their blood sugar is high. What's more, experiencing extreme thirst is one of the first signs of diabetes in those who have not been diagnosed.
  • Dementia: When someone has dementia, they are often unable to communicate they are thirsty—or they may not even recognize the feeling of thirst. For this reason, they are highly susceptible to dehydration.
  • Cancer: Dehydration is a common side effect of cancer treatment. Not only can radiation and chemotherapy cause dehydration, but people also experience diarrhea, vomiting, and other symptoms that can lead to dehydration.
  • Kidney disease: Your kidneys play an important role in removing water and waste from your body. But when you have kidney disease, your kidneys do not function as they should, increasing your risk for dehydration.

Experiencing Dehydration

If you are someone who frequently gets dehydrated due to your exercise schedule, work environment, or medical conditions, it is important to take steps to regularly hydrate your body.

It is also helpful to work with a healthcare provider on a hydration plan that works for you—especially because everyone's hydration needs are different. With careful planning and consistent hydration, you can reduce the likelihood that your dehydration escalates to a severe case requiring medical intervention.

Frequently Asked Questions

  • What fruits hydrate you fast?

    Typically, you get 20% of the fluid you need from the food you eat. Fruits with an 80% water content or more are a great choice for hydration. Some fruits have an even higher water content. For instance, strawberries and watermelon have 92% water content, and cucumbers have 96% water content.

  • Does coffee or tea dehydrate you?

    Because the caffeine in coffee and tea can have a slight diuretic effect—meaning it increases urine production—many people often assume that these beverages dehydrate you. However, some research has shown that the diuretic effect is minimal.

  • Can you drink lots of water and still be dehydrated?

    Medical conditions might play a role in your inability to quench your thirst. For instance, with diabetes insipidus, your kidneys are not able to retain water, which causes you to pass large amounts of urine despite drinking a lot.

  • How long does dehydration last?

    If your dehydration is moderate to severe, your recovery time will depend on the amount of fluids and electrolytes you need to become rehydrated. The cause of your dehydration also matters. Some medical conditions like kidney disease can cause chronic dehydration, so dehydration may be an ongoing issue.

Was this page helpful?
13 Sources
Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Taylor K, Jones EB. Adult dehydration. In: StatPearls. StatPearls Publishing; 2022.

  2. MedlinePlus. Dehydration.

  3. MedlinePlus. Dehydration.

  4. Centers for Disease Control and Prevention. Water and healthier drinks.

  5. Shaheen NA, Alqahtani AA, Assiri H, Alkhodair R, Hussein MA. Public knowledge of dehydration and fluid intake practices: variation by participants' characteristicsBMC Public Health. 2018;18(1):1346. doi:10.1186/s12889-018-6252-5

  6. Academy of Nutrition and Dietetics. How much water do you need.

  7. Centers for Disease Control and Prevention. Heat stress: Hydration.

  8. Reber E, Gomes F, Dähn IA, Vasiloglou MF, Stanga Z. Management of dehydration in patients suffering swallowing difficultiesJ Clin Med. 2019;8(11):1923. doi:10.3390/jcm8111923

  9. American Diabetes Association. Type 2 overview: Diabetes symptoms.

  10. Sfera A, Cummings M, Osorio C. Dehydration and cognition in geriatrics: A hydromolecular hypothesis. Front Mol Biosci. 2016 May 12;3:18. doi:10.3389/fmolb.2016.00018

  11. American Cancer Society. Dehydration and lack of fluids.

  12. UCLA Health. 15 foods that help you stay hydrated.

  13. Zhang Y, Coca A, Casa DJ, Antonio J, Green JM, Bishop PA. Caffeine and diuresis during rest and exercise: A meta-analysis. J Sci Med Sport. 2015 Sep;18(5):569-74. doi:10.1016/j.jsams.2014.07.017

Related Articles