Approved by the Cancer.Net Editorial Board, 07/2016

Dehydration occurs when a person does not take in enough fluid or loses too much fluid and cannot replace it. Every cell and organ depends on water, and without it the human body cannot function properly. The water in your body performs the following essential functions:

  • Removes waste and toxins

  • Transports nutrients and oxygen

  • Controls heart rate and blood pressure

  • Regulates body temperature

  • Lubricates joints

  • Protects organs and tissue, including the eyes, ears, and heart

  • Creates saliva

Although it is possible to go for a long time without food, people cannot live without water for more than a few days. People receiving cancer treatment may be at a higher risk for dehydration due to treatment side effects, such as diarrhea and vomiting.

Signs and symptoms of dehydration

The longer you go without taking in enough fluid, the more dehydrated you will become. Although thirst is one way your body alerts you to drink more, other symptoms of dehydration include:

  • A dry or sticky mouth or a swollen tongue

  • Fatigue or weakness

  • Irritability

  • Dizziness or lightheadedness

  • Nausea

  • Headaches

  • Constipation

  • Dry skin

  • Weight loss

  • Dark yellow urine or a decrease in urination

Severe dehydration, which can be life-threatening and needs immediate medical treatment, can cause the following symptoms:

  • Extreme thirst

  • Fever

  • Rapid heartbeat

  • Lack of urination for more than eight hours

  • Sunken eyes

  • Inability to sweat

  • Inability to produce tears

  • Low blood pressure

  • Disorientation or confusion

Talk with your health care team about any symptoms you may experience, including any new symptoms or a change in symptoms.

Causes of dehydration

You lose water every day through natural body functions, such as breathing, sweating, and going to the bathroom. Most people easily replace that fluid through drinking and eating. However, certain conditions affect the body’s ability to stay hydrated, requiring a conscious effort to take in more fluids. In fact, waiting to drink until you are thirsty is often not enough because you may be dehydrated and not feel thirsty.

Causes of dehydration include:

  • Diarrhea and vomiting. Cancer treatments, such as chemotherapy, can cause these side effects, which increase dehydration risk. If you have an ostomy or ileostomy your fluid needs may be very specific so talk with your health care team about how much fluid you need. Ostomies and ileostomies are surgical openings in the body that allow waste to exit.

  • Fever. A high fever can result in dehydration. People receiving cancer treatment may be at risk for developing infections that can cause fever.

  • Age. Infants, children, and older adults are at greater risk for dehydration. Although young children do not weigh much, they pass water and electrolytes out of the body frequently. Electrolytes are minerals that help regulate the body.

As a person gets older, the body slowly loses the ability to conserve water. Older adults are also at risk because they are less likely to sense that they are thirsty and may not eat or drink enough, especially if they live alone. Illnesses, disabilities, and some medications may also contribute to dehydration.

  • Chronic illness. Many diseases increase dehydration risk and/or the need for fluids. For example, people with uncontrolled diabetes urinate frequently. Kidney disease and cystic fibrosis (a disease in which thick mucus affects the lungs and digestive system) can also increase dehydration risk.

  • Medications. Some medications can cause a person to urinate or sweat more than normal. Talk with your health care team to find out if this is a possible side effect of any medications you are taking.

  • Fluid loss. If you have tubes that drain fluid this may cause you to lose extra fluid. You may need to replace these lost fluids by drinking more liquids to prevent dehydration.

  • Environment. Living, working, and exercising in a hot or humid environment increase the need for fluids. People living at high altitudes, from 8,000 feet to 12,000 feet above sea level, also need more fluids because their bodies lose water as they work to take in more oxygen.

  • Exercise. Everyone loses water through sweat, and people who engage in physical activity generally produce a significant amount of sweat. Even if you do not see sweat, you are likely sweating. The more you exercise, the more fluid you need to replace.

  • Other factors. Women and overweight or obese individuals are at greater risk for dehydration.

Diagnosing dehydration

Your doctor can use several different methods to diagnose dehydration, including:

  • Taking your vital signs, which include your temperature, blood pressure, and pulse.

  • Pressing on your fingertips. Fingertips that do not return to pink after pressing can indicate dehydration.

  • Gently pinching the skin on the back of your hand, arm, or other area. Skin that is slow to snap back can indicate dehydration.

Your doctor may also recommend laboratory tests, including:

  • Urine tests to determine the level of dehydration or to identify a health issue that may be causing dehydration

  • Blood tests to examine factors such as your electrolytes and kidney function

Treating dehydration

Relieving side effects is an important part of cancer care and treatment. This is called symptom management, palliative care, or supportive care. Treatment for dehydration depends on its severity. For mild dehydration:

  • Suck on ice chips or popsicles if you have trouble drinking or eating.

  • Apply moisturizer to cracked lips and medication to mouth sores so that drinking and eating are less painful.

  • If you are able to drink, take in small amounts of fluid frequently instead of a large amount at once. Drinking too much at once may cause vomiting.

  • Keep a water bottle with you at all times, and sip from it throughout the day.

  • Drink a large glass of water before bed and when you wake up each morning.

  • If you have diarrhea, choose beverages that have sodium and potassium to help replace these lost minerals.

  • If you have fatigue, keep ice and drinks within reach so you do not have to get up more often than necessary.

If you are not vomiting or experiencing diarrhea and are moderately dehydrated, your doctor may recommend your drink an oral rehydration solution. Severe dehydration requires fluids to be given intravenously (IV, through a vein).

Preventing dehydration

The following tips can help you keep your body's fluid balance in check.

  • Drink lots of fluids. The amount of fluid needed each day to stay hydrated depends on your health and lifestyle. Ask your doctor how much water you should drink. If you dislike plain water, try drinking flavored water or adding a slice of lemon. Other fluids, such as milk, juice, and tea, also count.

  • Eat foods with high water content. While drinking water is the best hydration source, many foods contain water and can help replenish lost fluids. Choose foods like lettuce (95% water), watermelon (92% water), and broccoli (91% water). Soups, popsicles, and yogurt also have high water content.

  • Manage side effects. If you are having a cancer treatment that is causing nausea, vomiting, or diarrhea, talk with your doctor about ways to prevent or manage these side effects.

  • Don't wait to drink. Make a conscious effort to drink enough on a regular basis and more often when you begin feeling ill, before you exercise, or before you go outside in hot weather. Ensuring that you are well hydrated before you lose water can help reduce your risk for dehydration.

More Information

Side Effects of Chemotherapy

When to Call the Doctor During Cancer Treatment

Nutrition Recommendations During and After Treatment

Additional Resource

MedlinePlus: Dehydration