Quick Overview
Dehydration occurs when the body loses more fluids than it takes in and no longer has enough water to function normally. Mild dehydration can often be managed with oral fluids, but severe dehydration is a medical emergency that requires prompt medical care. Knowing the warning signs can help you decide when urgent evaluation is necessary.
What Is Dehydration?
Dehydration happens when fluid loss exceeds fluid intake. Water is essential for normal bodily functions, including temperature regulation, circulation, and organ function. When dehydration becomes severe, these systems can be disrupted, leading to serious complications.
Anyone can become dehydrated, but the condition is more serious in infants, children, and older adults, who are more vulnerable to rapid fluid loss and its effects.
Common Causes of Dehydration
Verified causes of dehydration include:
- Not drinking enough fluids
- Excessive sweating, especially in hot weather or during physical activity
- Vomiting or diarrhea
- Fever or illness
- Certain medications, such as diuretics
- Medical conditions such as diabetes or kidney disease
Who Is Most at Risk?
Groups at higher risk for dehydration and its complications include:
- Infants and young children
- Older adults
- People with chronic medical conditions
- Individuals taking medications that increase urination
- People exposed to high heat or intense physical exertion
Dehydration Symptoms by Severity
Mild to Moderate Dehydration
Symptoms may include:
- Thirst
- Dry mouth or lips
- Fatigue
- Dark-colored urine or reduced urination
- Mild dizziness or lightheadedness
Mild to moderate dehydration often improves with oral fluids, including water or oral rehydration solutions.
Severe Dehydration
Severe dehydration can impair circulation and lead to complications. Symptoms may include:
- Inability to drink or keep fluids down
- Confusion or altered mental status
- Rapid heart rate
- Very low urine output
- Cool or clammy skin
Severe dehydration typically requires medical supervision and intravenous (IV) fluids.
When Is Dehydration an Emergency?
Dehydration becomes an emergency when symptoms are severe, worsening, or prevent adequate oral hydration, or when mental status changes occur. In these cases, medical treatment is needed right away.
Signs You Should Go to the ER for Dehydration
Emergency Warning Signs in Adults
Seek emergency care if dehydration is accompanied by:
- Confusion or disorientation
- Dizziness, fainting, or collapse
- Very little or no urination for an extended period
- Rapid heartbeat or rapid breathing
- Extreme weakness or lethargy
- Inability to keep fluids down due to vomiting
- Cool or clammy skin
- Seizures or loss of consciousness
Emergency Warning Signs in Babies and Children
Children can become dehydrated quickly. Emergency care is needed if a child shows:
- Very few or no wet diapers over several hours
- No tears when crying
- Sunken eyes
- A sunken soft spot on the head (fontanelle) in infants
- Unusual drowsiness, difficulty waking, or listlessness
- Irritability or confusion
Dehydration and Heat-Related Illness
Dehydration commonly occurs with heat exposure. Not drinking enough fluids during hot weather or physical exertion increases the risk of heat-related illnesses, including heat exhaustion and heatstroke. Heatstroke is a life-threatening condition and can be fatal without immediate medical treatment.
ER vs. Urgent Care for Dehydration
- Emergency care is recommended for severe symptoms, confusion, fainting, seizures, inability to keep fluids down, or signs of shock.
- Mild dehydration can often be managed outside the ER, but worsening symptoms should prompt emergency evaluation.
What Happens at the ER for Dehydration?
In emergency settings, clinicians may:
- Assess dehydration severity
- Check vital signs
- Perform blood tests to evaluate electrolytes
- Perform urine tests
- Provide oral fluids when possible
- Administer IV fluids for moderate to severe dehydration
- Monitor and correct electrolyte imbalances
- Observe patients until symptoms improve
Possible Complications of Severe Dehydration
If not treated promptly, severe dehydration can lead to:
- Electrolyte imbalances
- Kidney problems, including kidney failure
- Low blood pressure
- Shock
- Seizures
- Worsening heat-related illness
Some of these complications can be life-threatening.
How to Help Prevent Dehydration
Prevention focuses on maintaining adequate fluid intake:
- Drink fluids regularly, especially in hot weather or during illness
- Replace fluids lost through sweating, vomiting, or diarrhea
- Use oral rehydration solutions when recommended
- Monitor children and older adults closely
- Avoid prolonged heat exposure and take cooling breaks
- Include water-rich foods such as fruits and vegetables
When to See a Doctor or Call Emergency Services
Seek immediate medical care or call emergency services if dehydration is associated with:
- Loss of consciousness
- Severe confusion or disorientation
- Seizures
- Signs of shock
- Inability to keep fluids down
These symptoms may indicate a life-threatening emergency.
Frequently Asked Questions
When should you go to the ER for dehydration?
You should go to the ER if dehydration causes severe symptoms such as confusion, fainting, seizures, very low urine output, or inability to keep fluids down.
Is dehydration an emergency?
Dehydration can become an emergency when it is severe or prolonged. Mild dehydration is often manageable with oral fluids, but severe dehydration requires medical care.
Can dehydration cause fainting or seizures?
Yes. Severe dehydration can lead to fainting or seizures, often related to low blood pressure or electrolyte imbalances.
Can dehydration cause muscle cramps?
Yes. Muscle cramps are a recognized symptom of dehydration.
How long do people stay in the hospital for dehydration?
There is no high-quality evidence supporting a specific duration. Length of stay depends on severity, response to treatment, and individual health factors.
ER or urgent care for dehydration — which should I choose?
Emergency care is recommended for severe symptoms such as confusion, fainting, seizures, or inability to keep fluids down. Mild cases may not require ER care.
How much water should I drink to avoid dehydration?
There is no high-quality evidence supporting a single universal amount. Fluid needs vary based on age, activity level, weather, and health conditions.
What happens if you don’t drink water for 24 hours?
There is no high-quality evidence supporting a single predictable outcome. Effects vary widely depending on individual health and conditions.
APA References List
Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. (2024, September 10). Heat-related illnesses. https://www.cdc.gov/niosh/heat-stress/about/illnesses.html
Cleveland Clinic. (2023, June 5). Dehydration. https://my.clevelandclinic.org/health/diseases/9013-dehydration
Cleveland Clinic. (2024, October 1). Heat stroke: Symptoms, treatment & recovery. https://my.clevelandclinic.org/health/diseases/21812-heatstroke
Mayo Clinic Staff. (2025, May 2). Dehydration: Diagnosis & treatment. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/dehydration/diagnosis-treatment/drc-20354092
Mayo Clinic Staff. (2025, May 2). Dehydration: Symptoms & causes. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/dehydration/symptoms-causes/syc-20354086
MedlinePlus. (2023, August 5). Dehydration (MedlinePlus Medical Encyclopedia). National Library of Medicine. https://medlineplus.gov/ency/article/000982.htm
MedlinePlus. (2023, December 29). Dehydration. National Library of Medicine. https://medlineplus.gov/dehydration.html
National Health Service. (n.d.). Dehydration. https://www.nhs.uk/conditions/dehydration/
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.). Symptoms & causes of diarrhea. https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/symptoms-causesWhen to Go to the ER for Dehydration
Signs of a Dehydration Emergency
How to Use This Guide
This article is organized by severity and decision-making.
- Start with the Quick Overview if you need fast guidance.
- Use the Symptoms by Severity and ER vs. Urgent Care sections to decide where to seek care.
- Refer to When to See a Doctor and the FAQs for common questions based on verified medical evidence.
Quick Overview
Dehydration occurs when the body loses more fluids than it takes in and no longer has enough water to function normally. Mild dehydration can often be managed with oral fluids, but severe dehydration is a medical emergency that requires prompt medical care. Knowing the warning signs can help you decide when urgent evaluation is necessary.
What Is Dehydration?
Dehydration happens when fluid loss exceeds fluid intake. Water is essential for normal bodily functions, including temperature regulation, circulation, and organ function. When dehydration becomes severe, these systems can be disrupted, leading to serious complications.
Anyone can become dehydrated, but the condition is more serious in infants, children, and older adults, who are more vulnerable to rapid fluid loss and its effects.
Common Causes of Dehydration
Verified causes of dehydration include:
- Not drinking enough fluids
- Excessive sweating, especially in hot weather or during physical activity
- Vomiting or diarrhea
- Fever or illness
- Certain medications, such as diuretics
- Medical conditions such as diabetes or kidney disease
Who Is Most at Risk?
Groups at higher risk for dehydration and its complications include:
- Infants and young children
- Older adults
- People with chronic medical conditions
- Individuals taking medications that increase urination
- People exposed to high heat or intense physical exertion
Dehydration Symptoms by Severity
Mild to Moderate Dehydration
Symptoms may include:
- Thirst
- Dry mouth or lips
- Fatigue
- Dark-colored urine or reduced urination
- Mild dizziness or lightheadedness
Mild to moderate dehydration often improves with oral fluids, including water or oral rehydration solutions.
Severe Dehydration
Severe dehydration can impair circulation and lead to complications. Symptoms may include:
- Inability to drink or keep fluids down
- Confusion or altered mental status
- Rapid heart rate
- Very low urine output
- Cool or clammy skin
Severe dehydration typically requires medical supervision and intravenous (IV) fluids.
When Is Dehydration an Emergency?
Dehydration becomes an emergency when symptoms are severe, worsening, or prevent adequate oral hydration, or when mental status changes occur. In these cases, medical treatment is needed right away.
Signs You Should Go to the ER for Dehydration
Emergency Warning Signs in Adults
Seek emergency care if dehydration is accompanied by:
- Confusion or disorientation
- Dizziness, fainting, or collapse
- Very little or no urination for an extended period
- Rapid heartbeat or rapid breathing
- Extreme weakness or lethargy
- Inability to keep fluids down due to vomiting
- Cool or clammy skin
- Seizures or loss of consciousness
Emergency Warning Signs in Babies and Children
Children can become dehydrated quickly. Emergency care is needed if a child shows:
- Very few or no wet diapers over several hours
- No tears when crying
- Sunken eyes
- A sunken soft spot on the head (fontanelle) in infants
- Unusual drowsiness, difficulty waking, or listlessness
- Irritability or confusion
Dehydration and Heat-Related Illness
Dehydration commonly occurs with heat exposure. Not drinking enough fluids during hot weather or physical exertion increases the risk of heat-related illnesses, including heat exhaustion and heatstroke. Heatstroke is a life-threatening condition and can be fatal without immediate medical treatment.
ER vs. Urgent Care for Dehydration
- Emergency care is recommended for severe symptoms, confusion, fainting, seizures, inability to keep fluids down, or signs of shock.
- Mild dehydration can often be managed outside the ER, but worsening symptoms should prompt emergency evaluation.
What Happens at the ER for Dehydration?
In emergency settings, clinicians may:
- Assess dehydration severity
- Check vital signs
- Perform blood tests to evaluate electrolytes
- Perform urine tests
- Provide oral fluids when possible
- Administer IV fluids for moderate to severe dehydration
- Monitor and correct electrolyte imbalances
- Observe patients until symptoms improve
Possible Complications of Severe Dehydration
If not treated promptly, severe dehydration can lead to:
- Electrolyte imbalances
- Kidney problems, including kidney failure
- Low blood pressure
- Shock
- Seizures
- Worsening heat-related illness
Some of these complications can be life-threatening.
How to Help Prevent Dehydration
Prevention focuses on maintaining adequate fluid intake:
- Drink fluids regularly, especially in hot weather or during illness
- Replace fluids lost through sweating, vomiting, or diarrhea
- Use oral rehydration solutions when recommended
- Monitor children and older adults closely
- Avoid prolonged heat exposure and take cooling breaks
- Include water-rich foods such as fruits and vegetables
When to See a Doctor or Call Emergency Services
Seek immediate medical care or call emergency services if dehydration is associated with:
- Loss of consciousness
- Severe confusion or disorientation
- Seizures
- Signs of shock
- Inability to keep fluids down
These symptoms may indicate a life-threatening emergency.
Frequently Asked Questions
When should you go to the ER for dehydration?
You should go to the ER if dehydration causes severe symptoms such as confusion, fainting, seizures, very low urine output, or inability to keep fluids down.
Is dehydration an emergency?
Dehydration can become an emergency when it is severe or prolonged. Mild dehydration is often manageable with oral fluids, but severe dehydration requires medical care.
Can dehydration cause fainting or seizures?
Yes. Severe dehydration can lead to fainting or seizures, often related to low blood pressure or electrolyte imbalances.
Can dehydration cause muscle cramps?
Yes. Muscle cramps are a recognized symptom of dehydration.
How long do people stay in the hospital for dehydration?
There is no high-quality evidence supporting a specific duration. Length of stay depends on severity, response to treatment, and individual health factors.
Popular Questions People Ask
ER or urgent care for dehydration — which should I choose?
Emergency care is recommended for severe symptoms such as confusion, fainting, seizures, or inability to keep fluids down. Mild cases may not require ER care.
How much water should I drink to avoid dehydration?
There is no high-quality evidence supporting a single universal amount. Fluid needs vary based on age, activity level, weather, and health conditions.
What happens if you don’t drink water for 24 hours?
There is no high-quality evidence supporting a single predictable outcome. Effects vary widely depending on individual health and conditions.
References (APA 7th Edition)
Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. (2024, September 10). Heat-related illnesses. https://www.cdc.gov/niosh/heat-stress/about/illnesses.html
Cleveland Clinic. (2023, June 5). Dehydration. https://my.clevelandclinic.org/health/diseases/9013-dehydration
Cleveland Clinic. (2024, October 1). Heat stroke: Symptoms, treatment & recovery. https://my.clevelandclinic.org/health/diseases/21812-heatstroke
Mayo Clinic Staff. (2025, May 2). Dehydration: Diagnosis & treatment. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/dehydration/diagnosis-treatment/drc-20354092
Mayo Clinic Staff. (2025, May 2). Dehydration: Symptoms & causes. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/dehydration/symptoms-causes/syc-20354086
MedlinePlus. (2023, August 5). Dehydration (MedlinePlus Medical Encyclopedia). National Library of Medicine. https://medlineplus.gov/ency/article/000982.htm
MedlinePlus. (2023, December 29). Dehydration. National Library of Medicine. https://medlineplus.gov/dehydration.html
National Health Service. (n.d.). Dehydration. https://www.nhs.uk/conditions/dehydration/
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.). Symptoms & causes of diarrhea. https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/symptoms-causes