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.


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 mouthsores, or you’re sick to your stomach.


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.