What is Dehydration? What Causes It?

Dehydration happens when your body doesn’t have as much water as it needs. Without enough, your body can’t function properly. You can have mild, moderate, or severe dehydration depending on how much fluid is missing from your body.

Causes

It’s normal to lose water from your body every day by sweating, breathing, peeing, and pooping, and through tears and saliva (spit). Usually you replace the lost liquid by drinking fluids and eating foods that contain water. If you lose too much water or don’t drink and eat enough, you can get dehydrated.

You can lose more water than usual with:

  • A fever
  • Diarrhea
  • Vomiting
  • Excessive sweating
  • Peeing a lot (Diabetes and some medications like water pills -- also called diuretics -- can make you pee more often.)

You may not replace the water you lose because:

  • You’re busy and forget to drink enough.
  • You don’t realize you’re thirsty.
  • You don’t feel like drinking because you have a sore throat or mouth sores, or you’re sick to your stomach.

Symptoms

Signs of mild or moderate dehydration include:

  • Thirst
  • Dry or sticky mouth
  • Not peeing very much
  • Dark yellow pee
  • Dry, cool skin
  • Headache
  • Muscle cramps

Signs of severe dehydration include:

  • Not peeing or having very dark yellow pee
  • Very dry skin
  • Feeling dizzy
  • Rapid heartbeat
  • Rapid breathing
  • Sunken eyes
  • Sleepiness, lack of energy, confusion or irritability
  • Fainting

Symptoms for babies and young children can be different than for adults:

  • Dry mouth and tongue
  • No tears when crying
  • Dry diapers for 3 hours
  • Sunken eyes, cheeks, soft spot on the top of the skull
  • Sleepiness, lack of energy, or irritability

Severe dehydration is a medical emergency and needs to be treated immediately.

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Who’s at Risk?

Anyone can get dehydrated, but the odds are higher for some people:

  • Babies and young children are the most likely to have severe diarrhea and vomiting, and they lose the most water from a high fever. The youngest can’t tell you they’re thirsty or get their own drink.
  • Older adults have less water in their bodies and often don’t realize they’re thirsty. If they can’t get around very well anymore, they may not be able to get a drink easily.
  • People who are ill with a cold or sore throat may not want to eat or drink.
  • People with a chronic disease such as type 2 diabetes can pee a lot if the disease is uncontrolled. They also may take medicines such as water pills, which make them go more often.
  • People who are active outside in hot and humid weather sometimes can’t cool down effectively because their sweat doesn’t evaporate. This can lead to a higher body temperature and need for more water.
WebMD Medical Reference Reviewed by William Blahd, MD on May 02, 2017

Sources

SOURCES:

MedlinePlus: “Dehydration.”

Mayo Clinic: “Dehydration.”

Johns Hopkins Medicine Health Library: “Dehydration and Heat Stroke.”

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