Dehydration: Symptoms, Types, Causes and Treatment

Dehydration is a common and sometimes overlooked condition that affects people of all ages. Whether it’s due to illness, exercise, heatwaves, or simply forgetting to drink enough water, dehydration can have significant effects on the body’s normal functioning. Understanding its symptoms, types, causes, and most effective treatments is critical for maintaining health—especially for vulnerable groups like children and the elderly.

Symptoms of Dehydration

Recognizing the symptoms of dehydration early can make all the difference. The body gives clear signals when it's running low on fluids, but not all of them are obvious. Some people may experience only mild thirst, while others can develop severe symptoms that require immediate medical attention.

Symptom	Who is Affected	Severity	Source
Thirst	All ages	Mild to Severe	3 5 10
Dry mouth/tongue	All ages	Mild to Moderate	3 4 5 10
Decreased urine	All ages	Mild to Severe	2 10
Headache	Children, adults	Mild to Moderate	5 10
Fatigue	All ages	Mild to Severe	5 10
Sunken eyes	Children, elderly	Moderate/Severe	2 3
Poor skin turgor	Children, elderly	Moderate/Severe	1 2 3
Confusion	Elderly, terminally ill	Moderate/Severe	3 14
Dizziness	All ages	Moderate	10

Table 1: Key Symptoms

Understanding the Range of Symptoms

Dehydration doesn't always look the same. Mild dehydration might cause little more than thirst and a dry mouth, but even at this stage, there can be subtle effects on mood and concentration—especially in women and children 5 10. Moderate dehydration often brings more noticeable symptoms, including headaches, fatigue, decreased urine output (noticeably darker urine), and sometimes dizziness or lightheadedness 5 10.

Children

In infants and young children, dehydration can escalate quickly. Key signs include:

• Abnormal capillary refill time (taking longer than 2 seconds for color to return after pressing the skin)
• Absent tears when crying
• Dry mucous membranes (inside of the mouth, tongue)
• Sunken eyes
• General ill appearance

A combination of three or more of these findings is a strong indicator of dehydration in children 1 2.

Elderly

Older adults may not always feel thirsty, even when dehydrated. Instead, look for:

• Dryness and furrows on the tongue
• Dry mouth and mucous membranes
• Upper body muscle weakness
• Confusion or speech difficulties
• Sunken eyes

These signs are especially important as confusion and muscle weakness can easily be misattributed to other conditions in the elderly 3.

Mood and Cognitive Effects

Even mild dehydration—just a 1% loss of body weight—can affect mood, concentration, and cause headaches. This is particularly notable in healthy young adults but can impact all age groups 5.

Symptoms in the Dying and Terminally Ill

In terminally ill patients, symptoms like dry mouth and thirst are common, but not always directly linked to dehydration based on serum measurements. The relationship between hydration, symptom relief, and quality of life in these patients is complex and debated 4 14.

Types of Dehydration

Not all dehydration is created equal. The type depends on the balance of water and electrolytes lost, which shapes both the symptoms and the best way to treat it.

Type	Key Feature	Common Causes	Source
Isotonic	Equal loss of water and salt	Diarrhea, vomiting	6 7
Hypertonic (Water loss)	More water lost than salt	Fever, sweating, diabetes	6 7
Hypotonic (Salt loss)	More salt lost than water	Diuretics, salt-wasting conditions	6 7

Table 2: Types of Dehydration

Isotonic Dehydration

This is the most common type, especially in children. Both water and sodium (salt) are lost in roughly equal amounts, leading to decreased volume in the bloodstream and tissues. Typical causes include diarrhea and vomiting 6 7.

Hypertonic Dehydration (Water Loss)

Here, the body loses more water than salt, raising blood sodium levels (hypernatremia). This type is often caused by prolonged fever, excessive sweating, inadequate water intake, or uncontrolled diabetes. Symptoms may include intense thirst and neurological disturbances 6 7.

Hypotonic Dehydration (Salt Loss)

In this scenario, more sodium is lost than water, lowering blood sodium (hyponatremia). It can result from diuretic use, adrenal insufficiency, or certain kidney problems. The loss of sodium is more dangerous than water loss because it can lead to circulatory collapse, especially if not recognized and treated appropriately 6 7.

Causes of Dehydration

Dehydration can result from a range of everyday factors or underlying health issues. Knowing the cause is key to both prevention and effective treatment.

Cause	Typical Triggers	At-Risk Groups	Source
Diarrhea/Vomiting	Infection, food poisoning	Children, elderly	2 6 10
Excessive sweating	Heat, exercise	Athletes, outdoor workers	5 7 10
Inadequate intake	Poor access, neglect, confusion	Elderly, infants	3 6 10
Fever	Infection	All ages	6 7
Medications	Diuretics, laxatives	Chronic illness patients	6 7
Chronic disease	Diabetes, kidney issues	All ages	6 7

Table 3: Common Causes of Dehydration

Gastrointestinal Losses

The most frequent cause is acute illness leading to diarrhea and vomiting. This is why dehydration is a major concern during episodes of gastroenteritis, particularly in children and the elderly 2 10.

Excessive Sweating and Environmental Exposure

People who work or exercise in hot environments can quickly become dehydrated from sweat losses. Athletes are especially at risk, as even mild dehydration impairs mood and concentration 5 10.

Insufficient Fluid Intake

Some people simply do not drink enough, either due to poor access to water, a diminished sense of thirst (as seen in the elderly), or confusion and cognitive impairment 3 6 10. Infants are also at higher risk because they rely on caregivers to provide fluids.

Medical and Drug-Related Causes

Certain medications, especially diuretics and laxatives, can increase fluid loss. Chronic diseases like diabetes (due to high blood sugar leading to increased urination) and kidney disorders can also promote dehydration 6 7.

Special Considerations: The Elderly and Terminally Ill

Elderly individuals may have a reduced sense of thirst, and those with mobility or cognitive issues may be unable to access fluids easily. In terminally ill patients, dehydration may result from a combination of decreased intake, increased losses, and disease processes. The role of artificial hydration in this group remains controversial 3 4 14.

Treatment of Dehydration

Prompt and appropriate treatment can quickly reverse dehydration and prevent serious complications. The approach depends on the severity and underlying type.

Treatment	Best For	Notes	Source
Oral Rehydration (ORT)	Mild/moderate	First-line in most cases	11 12
Intravenous fluids	Severe, unable to tolerate ORT	Urgent cases, shock	12 13
Subcutaneous fluids (hypodermoclysis)	Mild/moderate, elderly	Alternative to IV	6 14
Treat underlying cause	All	E.g., stop vomiting, treat infection	6

Table 4: Treatment Approaches

Oral Rehydration Therapy (ORT)

ORT involves drinking a solution of water, salts, and sugar (glucose). It is highly effective and safe for most cases of mild to moderate dehydration, especially in children with diarrhea 11 12.

• How it works: The glucose helps the intestine absorb sodium and water more effectively.
• Effectiveness: Studies show ORT is as effective as intravenous fluids in most cases, with fewer complications and a shorter hospital stay 12.
• When to use: Whenever the person can drink and is not vomiting persistently.

Intravenous Fluids

For severe dehydration, or when oral fluids cannot be kept down due to vomiting or altered consciousness, intravenous (IV) fluids are necessary. Rapid restoration of circulating volume is especially important in shock 12 13.

• Recommendations: Rapid (1–2 hour) IV fluid replacement is favored over slower “deficit therapy” because it restores circulation quickly and allows for earlier resumption of oral feeding 13.

Subcutaneous Fluids (Hypodermoclysis)

This method involves infusing fluids just under the skin. It’s particularly useful for mild to moderate dehydration in elderly or palliative care patients, especially when IV access is difficult 6 14.

Treating the Underlying Cause

Addressing the root cause—whether it’s stopping diarrhea, treating an infection, or adjusting medications—is essential for preventing recurrence 6.

Special Considerations in the Terminally Ill

The decision to treat dehydration in terminally ill patients is complex. While some symptoms (like delirium or confusion) may improve with hydration, others (such as thirst or dry mouth) may not, and over-hydration can lead to additional problems. The benefits and burdens of artificial hydration should be weighed individually 4 14.

Conclusion

Dehydration is a multifaceted clinical problem, but one that is largely preventable and treatable when recognized early. Here’s a summary of the key points:

• Symptoms range from thirst and dry mouth to confusion, sunken eyes, and poor skin turgor. Children and the elderly may show distinct signs 1 2 3 5 10.
• Types of dehydration are classified by the balance of water and sodium lost: isotonic, hypertonic, and hypotonic, each with unique implications 6 7.
• Causes include diarrhea, vomiting, excessive sweating, insufficient intake, certain medications, and chronic diseases. Elderly and infants are especially vulnerable 2 3 6 7 10.
• Treatment is centered on oral rehydration for mild/moderate cases, intravenous fluids for severe cases, and subcutaneous fluids as an alternative in some populations. Treating the underlying cause and careful consideration in terminally ill patients are crucial 6 11 12 13 14.

Staying hydrated is a simple yet powerful way to support overall health—recognize the signs, understand the risks, and respond quickly to keep yourself and those you care for safe.