Dehydration: Symptoms, Causes and Complications

Dehydration is a condition that can occur when the loss of body fluids, mostly water, exceeds the amount that is taken in and your body does not have enough water and other fluids to carry out its normal functions.

Updated: June 16, 2022

Dehydration is a condition that can occur when the loss of body fluids, mostly water, exceeds the amount that is taken in and your body does not have enough water and other fluids to carry out its normal functions.
Our body contains almost 75 percent water, and it is essential for our survival. Even low levels of dehydration can cause headaches, lethargy, and constipation. Water is found inside cells, within blood vessels, and between cells in our body. Our bodies have its own water management system and the thirst mechanism tells us when we need to increase fluid intake.
Water is constantly lost throughout the day as we breathe, sweat, urinate and defecate . Along with the water, small amounts of salts or electrolytes are also lost. This loss can be replaced by drinking fluids. If dehydration begins to occur, our body will move water around to the areas where it is needed.
Dehydration can be easily reversed by increasing fluid intake that contain electrolytes or salts that are lost during activity, but severe cases of dehydration require immediate medical attention. Although infants and children are at highest risk for dehydration, many adults and especially the elderly have significant risk factors.

Symptoms of Dehydration:

The most common symptoms of dehydration include thirst, darker urine, and decreased urine production. The color of urine is one of the best indicators of hydration level of a person. Clear urine indicates you are well hydrated where as darker urine means you are dehydrated.
Usually in older adults, dehydration can occur without thirst. This is why it is important to drink more water when ill or during hot weather.
As the condition progresses from mild to moderate dehydration, symptoms include:

  •     dry mouth
  •     lethargy
  •     headache
  •     weakness in muscles
  •     dizziness

Symptoms of severe dehydration include:

  •     lack of sweating
  •     sunken eyes
  •     shriveled and dry skin
  •     delirium
  •     fever
  •     low blood pressure
  •     increased heart rate
  •     unconsciousness

Symptoms of dehydration in infants and children may include:

  •     a sunken fontanel (soft spot on the top of the head)
  •     no wet diaper for 3 or more hours
  •     dry tongue and mouth
  •     irritable
  •     no tears when crying
  •     sunken cheeks and/or eyes

Causes of Dehydration:

Dehydration can be due to not drinking enough water, losing too much water or a combination of both. When you are sick or busy, or because you lack access to safe drinking water when you are traveling, hiking or camping, it is not possible to drink enough water.
Other dehydration causes include:


This is the most common cause of dehydration and related deaths. Diarrhea prevents absorption of water from food in large intestine. The body excretes too much water, leading to dehydration.

Vomiting :

This leads to a loss of fluids and makes it difficult to replace water by drinking. If you have vomiting along with diarrhea, you lose even more fluids and minerals. 

Sweating :

The cooling mechanism of your body releases a significant amount of water. Hot and humid weather and vigorous physical activity can further increase fluid loss from sweating. Similarly, a fever can cause an increase in sweating and may dehydrate the patient, especially if there is also diarrhea and vomiting.

Diabetes :

High blood sugar levels cause increased urination and fluid loss.

Frequent urination :

This is caused by certain medical condition especially uncontrolled diabetes. But also can be due to alcohol and medications such as diuretics, antihistamines, blood pressure medications and antipsychotics.

Burns :

Blood vessels can become damaged, causing fluid to leak into the surrounding tissues.

Complications of Dehydration:

Untreated dehydration can lead to serious complications which can include:

Hypovolemic shock or Low blood volume shock:

This is one of the most serious, and sometimes life-threatening, complications of dehydration. It occurs when low blood volume causes a drop in blood pressure and a reduction in the amount of oxygen reaching tissues in your body.

Heat injury:

If you do not drink enough fluids when you are exercising vigorously, you may end up with a heat injury. This could be ranging in severity from mild heat cramps to heat exhaustion or potentially life-threatening heatstroke.


This is due to electrolyte imbalance. Electrolytes such as potassium and sodium help carry electrical signals from cell to cell. If your electrolytes are out of balance, the normal electrical messages can become mixed up which can lead to involuntary muscle contractions and sometimes to a loss of consciousness.

Urinary and kidney problems:

Prolonged or repeated cycle of dehydration can cause urinary tract infections, kidney stones and even kidney failure.

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