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Managing Cancer Care

Dehydration and Lack of Fluids

The cells in your body must have a certain amount of liquid to function well. This is called hydration or being hydrated.

When you don't have enough fluid in your body or do not have enough where it’s needed in the body it is called dehydration.

What causes dehydration?

When your body puts out more fluid than it takes in, you can become dehydrated. A person can become dehydrated for many reasons, whether they have cancer or not. It can happen because a person does not eat or drink enough, or because they are losing excessive amounts of fluids.

Here are some conditions or side effects that can lead to dehydration in a person who has cancer:

  • Vomiting
  • Diarrhea
  • Fever with or without an infection
  • Bleeding
  • Loss of appetite or simply not taking in enough fluids; Keep in mind that fluid comes from both food and drink, so a person who isn’t eating must drink more to make up the difference.
  • Procedures and surgeries can cause fluid to be lost

What to look for

  • Dry mouth and lips
  • Thirst
  • Dizziness or weakness
  • Trouble swallowing dry food
  • Dry, sticky mouth that makes it hard to talk
  • Dry skin, skin that “tents” (stays up) when lightly pinched
  • A swollen, cracked, or dry tongue
  • Higher than normal body temperature with or without chills
  • Rapid weight loss (See Weight Changes)
  • Little or no urine
  • Constipation
  • Fatigue
  • Sunken eyeballs
  • Poor appetite and no thirst (Dehydrated people often feel less hungry and thirsty.)

What the patient can do

  • Keep a food and fluid diary.
  • Drink fluids. Sometimes iced fluids are easier.
  • Remember that food contains fluid. Try to eat fruits, vegetables, soups, gelatins, Popsicles, and other moist foods.
  • Use lotion often to soften dry skin.
  • Try to get rid of the cause of dehydration, such as vomiting, diarrhea, or fever. (See these sections for information on these causes.)
  • Apply lubricant to lips to avoid painful cracking.
  • Fill a small cooler with juice boxes, bottled water, or other drinks and keep it next to you, if it’s tiring to get up.
  • Suck ice chips to relieve dry mouth if you can’t drink enough liquid.

What caregivers can do

  • Offer cold or cool liquids every hour or so. If the patient is very weak, try giving liquids with a small medication syringe that you can get at a pharmacy.
  • Encourage the patient to eat small meals several times a day if they can.
  • Include moist foods, soups, and fruit smoothies (made with ice in a blender) as snacks.
  • Keep an intake and output diary by tracking food and fluid intake and by watching the urine output.
  • Check the patient often to be sure they haven’t become confused.
  • When the patient stands up after sitting or when getting up from bed, encourage them to do it slowly. Stand nearby, in case they get dizzy or feel faint.
  • If the patient gets dizzy or feels faint, offer fluids and have them sit or lie down.

Call the cancer care team if the patient

  • Can’t take in or hold down liquids
  • Has vomiting, diarrhea, or fever that last for more than 24 hours
  • Has urine that’s either very dark or only comes in a small amount, or if there’s no urine for 12 hours or more
  • Has dizziness or faints when standing up, even after drinking fluids
  • Becomes confused or disoriented

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

Besser J, Grant BL, American Cancer Society. What to Eat During Cancer Treatment. Atlanta, GA: American Cancer Society; 2018.

Gallegos C, Brito-de la Fuente E, Clave P, Costa A, Assegehagn G. Nutritional aspects of dysphagia management. Adv Food Nutr Res. 2017;81:271-318.

National Comprehensive Cancer Network (NCCN). Clinical practice guidelines in oncology: Palliative care. Version 2.2019. Accessed at on January 21, 2020.


Last Revised: February 1, 2020

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