Dehydration: Signs, Symptoms, Causes, and Prevention

Things to Know about Dehydration

Dehydration refers to a state of reduced total body water (TBW) volume below the normal level due to mainly intracellular fluid loss without a proportional reduction in cellular electrolytes such as sodium and potassium. Physiologically, dehydration simultaneously occurs with hypovolemia, which refers to a state of extracellular volume depletion. Dehydration and/or hypovolemia, which both essentially describe states of body fluid loss, occur when fluid losses exceed fluid intake, as seen with gastrointestinal, renal, or skin losses.

Common manifestations of total body water volume depletion vary based on the degree of fluid floss but can include increased thirst, lassitude, postural dizziness, prolonged capillary refill time, decreased urine output, muscle cramps, abnormal vital signs, sunken eyes, dry mucous membranes, decreased skin turgor, as well as symptoms and signs of electrolyte abnormalities.

Additional complications relating to dehydration and hypovolemia are rare because the human body has compensatory mechanisms that serve to protect against the development of excessive fluid loss. In rare circumstances, hypovolemic shock, renal failure, thrombosis, as well as dangerous metabolic and neurological syndromes may complicate dehydration and/or hypovolemia.

What is Dehydration?

Dehydration is body water loss without a proportional reduction in sodium and potassium. This causes water to move from the intracellular into the extracellular fluid compartment. The net result of dehydration is approximately75% intracellular fluid loss and a resultant rise in serum sodium concentration in the blood known as hypernatremia.

Dehydration usually occurs concurrently with hypovolemia. Hypovolemia, or intravascular volume depletion, occurs when sodium-containing isotonic fluids are lost from the gastrointestinal tract, in urine, from the skin, or are sequestered into internal spaces.

Dehydration and hypovolemia are frequently used interchangeably, even in medical literature and by medical doctors. These two conditions are associated with different pathophysiologic mechanisms and produce different clinical symptoms and signs.

Since dehydration and hypovolemia often coexist in an individual, this article will discuss a syndrome of overall fluid loss, which contains aspects of both dehydration and hypovolemia, resulting in total body water reduction.

Depletion of body water results from increased fluid loss, decreased fluid intake, or both.

The most common sources of increased fluid loss include the following factors.

  • Gastrointestinal losses: vomiting, diarrhea
  • Renal losses: excessive diuretic use, diabetes, and other complex pathologies
  • Skin losses: sweating, burns, fever

The most common causes of decreased fluid intake include the following factors.

  • Insufficient water intake, particularly in debilitated or critically ill elderly individuals.
  • Illnesses such as pharyngitis and tonsillitis when individuals have difficulty (dysphagia) or pain (odynophagia) during swallowing and may avoid fluid intake.

Fluid volume depletion can manifest in a variety of symptoms and signs. General symptoms include thirst, headache, lack of energy, weakness, postural dizziness, and fatigue. Physically an individual may have dry skin, dry mucus membranes, and reduced tears. Dehydrated and hypovolemic patients often have a variety of hemodynamic, metabolic, and electrolyte abnormalities that are not readily appreciable in non-clinical settings.

What are the Levels of Dehydration?

The levels of dehydration are as follows.

  • Mild: 3-5% weight loss
  • Moderate: 6-9% weight loss
  • Severe: Greater than 10% weight loss or severe.

These levels are defined in a study on dehydration and volume depletion published in the World Journal of Nephrology.

Mild dehydration occurs when fluid depletion results in 3-5% weight loss. Mild dehydration is characterized by slightly increased thirst and possibly slightly decreased urinary output. Cognitive function, vital signs, capillary refill time of less than 2 seconds, and the appearance of eyes, skin, and mucous membranes all remain normal.

Moderate dehydration occurs when fluid depletion results in 6-9% weight loss. Moderate dehydration is characterized by the following symptoms.

  • Lack of energy or lassitude in adults
  • Irritability in children
  • Moderately increased thirst
  • Elevated heart rate
  • Decreased blood pressure, especially blood pressure that drops soon after standing
  • Weak pulse
  • Increased respiratory rate
  • Sunken eyes and decreased flow of tears or lacrimation
  • Cool, clammy skin with reduced elasticity
  • Moderately delayed capillary refill time of 2-3 seconds
  • Dry mucous membranes
  • Moderately decreased urinary output

Severe dehydration occurs when fluid depletion results in more than 10% weight loss. It is also called hypovolemic shock. Severe dehydration is characterized by the following symptoms.

  • Impaired consciousness and drowsiness
  • Marked irritability in children
  • Extreme thirst
  • Variable heart rate depending on degree of fluid loss
  • Marked decrease in blood pressure
  • Peripheral pulses that are almost absent and difficult to appreciate
  • Abnormal breathing patterns and decreased rate of breathing
  • Deeply sunken eyes and absent lacrimation
  • Cold, clammy skin with patchy and irregular colors
  • Markedly decreased skin elasticity, the skin will “tent” upon being pulled
  • Markedly delayed capillary refill time of greater than 3 seconds
  • Extremely dry mucous membranes
  • Markedly decreased or completely absent urine production

The three levels of dehydration are compared in the following chart.

Mild, moderate, and severe dehydration compared

What are the Causes of Dehydration?

The causes of dehydration include the following factors.

  • Not drinking enough water
  • Increased fluid loss through the gastrointestinal tract
  • Increased fluid loss through the kidneys 
  • Increased fluid loss through the skin

Insufficient fluid intake that fails to replace fluids lost through normal physiologic processes can be a cause of dehydration. Conditions that can lead to decreased fluid intake include impaired or altered mental activity, neurologic diseases which impair the thirst mechanism, head and neck diseases that cause difficulty or pain with swallowing, old age, severe debilitation, and voluntary refusal to drink water such as during fasting.

The amount of water to drink varies based on gender, climate, and physical activity among other factors, though 2-3 liters per day is a good starting basis for consideration.

Fluid losses through the gastrointestinal tract are significant contributors to dehydration. Vomiting and diarrhea can produce significant dehydration, particularly in children and the elderly. According to the Mother and Child Health and Education Trust, dehydration related to diarrheal diseases is one of the biggest killers of children in the modern world, killing approximately 2.2 million children every year, 80% of whom are 2 years old or younger.

Renal causes of excessive fluid loss leading to dehydration are mostly related to chronic diseases of the kidney or medications used to control hypertension. Fluid loss through the skin can occur during periods of excessive sweating and heat, burns, or dermatological diseases which affect the integrity of the skin.

This diagram shows the main causes of dehydration.

Dehydration can be caused by what we take into the body, and by how our bodies work

What Foods and Drinks can Cause Dehydration?

Foods and drinks that can cause dehydration include herbs and berries that possess “natural diuretic” properties as well as caffeinated beverages and alcohol.

  • Certain herbs and berries: Parsley, dandelion, hawthorn, and juniper are thought to possess diuretic properties, which means that they increase the production of urine by the kidneys. According to registered dietitian Julia Zumpano, RD, LD in a discussion about a similar topic with the Cleveland Clinic, “Herbs are not regulated or researched very well...” This means that the mechanisms by which these herbs and berries cause diuresis is not well known.
  • Caffeine found in coffee, tea, and other beverages: Caffeine is another natural diuretic. Caffeine is a methylxanthine compound that is able to increase urine output by increasing cardiac output and the net filtration rate in the kidneys. So does coffee dehydrate you? Yes, it can.
  • Alcohol: The dehydration of alcohol is because it is a diuretic, but the exact mechanisms of how alcohol and/or its metabolites increase urine production are unknown. The commonly accepted theory is that alcohol acts both directly and indirectly to inhibit the release of a pituitary hormone called vasopressin (antidiuretic hormone), which plays a major role in the regulation of water excretion. (R.M. Hobson 2010, Hydration Status and the Diuretic Action of a Small Dose of Alcohol.)

These foods and drinks that dehydrate you are not the only ones, but they are very common examples.

Who is at most Risk of Dehydration?

Those most at risk of dehydration are the following groups.

  • Infants and children: The pediatric population is more prone to dehydration because infants and children have higher metabolic needs that make them more susceptible to dehydration, experience increased insensible losses, and are often unable to communicate their needs or hydrate themselves, according to the American Academy of Pediatricians.
  • The elderly: The geriatric population is more likely to develop dehydration due to immobility from falls or debilitating illness, impaired thirst mechanism, and chronic diseases such as diabetes and renal diseases.
  • Outdoor workers:  Those who work or perform some other physical activity outdoors during hot conditions such as athletes, landscapers, or construction workers are also at increased risk of dehydration.

What are the Symptoms of Dehydration?

The symptoms of dehydration include the following signs.

  • Dry mouth and tongue
  • Increased thirst
  • Lack of energy (lassitude)
  • Postural dizziness
  • Prolonged capillary refill time
  • Decreased urine output
  • Muscle cramps
  • Abnormal vital signs
  • Sunken eyes
  • Dry mucous membranes
  • Decreased skin turgor
  • Signs of electrolyte abnormalities
  • Dehydration headache
  • Kidney pain dehydration and flank pain

This diagram lists some signs of potentially very serious dehydration.

Potential symptoms of major dehydration

Does Dehydration Cause Cramping?

Dehydration can cause cramping.

A muscle cramp is a sudden, involuntary, and painful contraction of one or more muscles according to Mayo Clinic. These cramps are frequently encountered in athletes during and after exercise. The current knowledge suggests that these exercise-associated muscle cramps (EAMC) are induced by either loss of electrolytes and fluid during exercise (dehydration-electrolytes theory) or by complex neurological mechanisms (neural theory).

The dehydration-electrolytes theory says hydration and muscle cramping are related in that the loss of fluid and essential electrolytes like sodium and potassium may be responsible for muscle cramps. However, research from Edith Cowan University (ECU) published in the Journal of the International Society of Sports Nutrition suggests that electrolyte loss rather than pure water loss is responsible for EAMCs.

Does Dehydration Cause High Blood Pressure?

Dehydration may transiently cause high blood pressure, although the link between water and blood pressure is normally one of dehydration lowering blood pressure.

The pumping of the heart results in pulsatile blood flow which exerts pressure against the walls of blood vessels. Factors determining blood pressure include cardiac output, volume and viscosity of blood, elasticity of vasculature, and other complex physiologic regulatory mechanisms.

Blood pressure during states of dehydration is more commonly low as blood volume due to fluid loss is decreased. This is referred to as hypotension and is a useful marker for moderate to severe dehydration.

During severe dehydration, transient increases in blood pressure may also be noted. This is the result of compensatory mechanisms which sense low circulating blood volume and constrict peripheral arteries to keep central organs such as the heart, brain, and kidney perfused. This creates a circulatory loop with a lesser volume in which the remaining blood volume can exert a higher pressure on vessels.

These are some of the fluids you can drink to help you recover from dehydration.

Rehydration is achieved by taking in more fluids, which can be more than just water

Does Dehydration Cause Diarrhea?

Dehydration does not cause diarrhea, but diarrhea can cause dehydration.

The World Health Organization (WHO) defines diarrhea as 3 or more loose or watery stools per day or more frequent passage than is normal for the individual.Diarrhea is an important cause of dehydration, particularly in children.

Can Dehydration Cause Fever?

Dehydration can cause a fever.

Fever is defined as an elevation of normal body temperature, usually greater than 38°C (100.4°F). Dehydration, particularly in the setting of heat exhaustion or heat stroke, can be associated with hyperthermia and fever-like symptoms due to dysregulation of central nervous system temperature regulation.

Can Dehydration Cause Headache?

Dehydration can cause headaches.

Dehydration is associated with intravascular volume contraction, which means there is less circulating blood volume. This can lead to decreased blood flow to the brain, which makes brain tissue shrink. The contracture of cerebral tissue can tug on nerves and vasculature leading to variable pain or headache, according to the National Headache Foundation.

What are the Complications of Dehydration?

The complications of dehydration include hypovolemic shock, renal failure, thrombosis, and dangerous metabolic and neurological syndromes that may complicate dehydration and/or hypovolemia.

Hypovolemic shock, which is characterized by circulatory collapse from intravascular fluid volume loss, is life-threatening. Poor perfusion during hypovolemic shock can have devastating effects on the brain, heart, and kidneys.

  • Effect on brain function: Hypertonic dehydration, which refers to the loss of water without a proportional reduction in electrolytes such as sodium and potassium, can have devastating effects on the brain. One such condition is Osmotic demyelination syndrome which is caused by acute severe hypernatremia which may occur in hypertonic dehydration (increased levels of sodium relative to water in the body). This condition is associated with loss of myelin insulation of central nervous system nerves which can lead to an altered level of consciousness, coma, locked-in syndrome, dysarthria, dysphagia, diplopia, and/or worsening quadriparesis.
  • Effect on heart function: Major intravascular fluid volume loss can lead to hemoconcentration, which is the formation of thickened, viscous blood which is prone to clotting and thrombus formation. A 2020 study from Hangzhou Normal University and the Aged Care Hospital Zhejiang in China found that acute heart failure patients with higher hemoconcentration were almost twice as likely to die within 2 years.
  • Effect on kidneys: In severely dehydrated patients acute kidney injury and renal failure may occur.

How is Dehydration Diagnosed?

Dehydration is diagnosed mainly by clinical assessment of symptoms and signs, which is then supported by laboratory analysis of blood and urine parameters by medical professionals. The clinical assessment for dehydration and hypovolemia involves a physical exam involving mainly the nervous system, cardiovascular system, and urinary system.

In adults, one can suspect dehydration when the following symptoms and signs are present.

  • Feeling tired
  • Feeling dizzy or lightheaded 
  • Feeling confused and disorientated
  • Feeling thirsty
  • Dry mouth, lips, and eyes
  • Weak and rapid pulse
  • Dark yellow and strong-smelling urine
  • Decrease in urine volume or frequency

In children, under the age of 5, one can suspect dehydration when the following symptoms and signs are present.

  • Drowsiness 
  • Irritability 
  • Rapid breathing
  • Few or no tears when crying
  • Sunken fontanelle (soft spot on an infant's head that bulges inward)
  • Dry mouth 
  • Dark yellow urine
  • No urination in last 12 hours
  • Cold, clammy, or mottled extremities 

The following diagram shows the different dehydration signs for children versus adults.

Children suffering from dehydration may show different symptoms than adults

What is the Treatment for Dehydration?

The treatment for dehydration is fluid replacement. The volume, composition, rate, and type of fluid replacement therapy is based on the degree of dehydration and hypovolemia, and the decision on how to perform the fluid replacement should be made by a medical professional. Besides for water, an oral rehydration solution (ORS) is frequently used, consisting of water, glucose, sodium, and potassium. There are numerous commercially available oral rehydration solutions that can be used during mild or even moderate dehydration, particularly in the setting of diarrhea.

This video from the UK’s St. John Ambulance first aid charity explains how to help someone who is suffering from dehydration.

Oral rehydration therapy is used for treating mild dehydration in both children and adults. This is for situations where patients have no hemodynamic instability such as low blood pressure and high heart rate, no depressed mental status, no refractory vomiting, and no comorbid conditions such as diabetes, heart failure, or kidney failure which could complicate dehydration.

This is a sample Oral Rehydration protocol, but following directions on the specific ORS purchased is most appropriate.

Sample Oral Rehydration Protocol for Dehydration 


Recommended ORS volume to provide over first 4 hours of fluid replacement therapy

How to administer



~2-4L for average(70kg) adult 

After determining the appropriate volume of ORS based on weight, divide this volume into smaller amounts to be given every 5 minutes over the course of 4 hours. 



~40-5.5 for average(70kg) adult

Adopted from Powers KS. Dehydration: Isonatremic, Hyponatremic, and Hypernatremic Recognition and Management. Pediatr Rev .2015; 36(7): p.274-285.

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