By , July 26th 2013. Last reviewed 31st December 2022.

What is a medical definition of dehydration?

The term dehydration refers to a lack of water in your body; it originates from the Latin “de-” (removal) and Greek “hydros” (water). By definition, dehydration is a loss of more than 1% of body weight due to a water loss [1,2]. So, if you weigh 150 pounds and unintentionally lose more than 1.5 pounds in a short time (few hours to days), you can assume you are dehydrated.

Synonyms for dehydration include hypohydration and water deficiency.

What does dehydration mean in lay terms?

Dehydration means “dryness of the body.” What happens to your body during dehydration is similar to what happens to a plum when it dries and turns into a prune.

Why do we need water?

Most processes in the body cells can occur only in the presence of water. Water also enables the blood flow, excretion of waste substances with the urine, lubrication of the gastrointestinal and respiratory tract and sweating. Without sufficient amount of water, your body cannot function properly [2,3].

Symptoms and Signs

  • Mild dehydration: thirst, dry mouth, increased heart rate, dark yellow urine (check urine color chart) and 1-3% loss of body weight.
  • Moderate dehydration: dry lips, tiredness, dizziness, dark yellow urine and 4-6% loss of body weight.
  • Severe dehydration: severe thirst, fatigue and headache, brown urine and loss of more than 6% of body weight.

Dehydration is considered acute when it lasts for a day at most, and chronic when it lasts for more than a day.


Dehydration develops when you consume less water than you lose from your body. Common causes:

  • In infants and small children: diarrhea
  • In adults: insufficient drinking, excessive sweating, severe diarrhea or vomiting, excessive urination
  • In elderly: insufficient drinking due to decreased sense of thirst, diuretics use

Anyone can get dehydrated in any part of the year: in summer, winter or at any time.

Diagnosis and Treatment

A doctor can make a diagnosis of dehydration from symptoms, signs, skin turgor test and blood and urine tests.

Treatment of mild and moderate dehydration is by drinking water and of severe dehydration by an infusion of the fluids into a vein.


If severe dehydration is not treated promptly, it can result in serious complications, such as seizures, hypovolemic shock, heat stroke, acute kidney failure or blood clots and, eventually, death.

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