Dehydration: Symptoms, Causes, Treatment & Red Flags

Introduction

Dehydration occurs when fluid loss is greater than fluid intake ^[1,5]. The body then lacks enough fluid to work as it should ^[1,5].

Too little fluid intake can cause dehydration ^[1,2]. A rise in fluid loss can also cause it [1-3]. In many cases, both problems occur at once ^[2,3].

Common causes include vomiting, diarrhea, fever, and heavy sweating ^[1,2]. Frequent urination and not drinking enough are also common causes ^[1,2].

Anyone can become dehydrated ^[5]. Risk is higher for babies, children, older adults, and people with long-term health problems ^[3,5]. Athletes and people active in hot places also face added risk ^[2,9].

This guide covers dehydration symptoms, causes, treatment and emergency warning signs. It also explains how signs may differ by age.

Overview: What Dehydration Is and Why It Matters

How fluid loss affects the body

The body loses water each day through sweat, urine, stool, tears, and breathing ^[10]. Drinks and foods that contain water replace these normal losses ^[10].

Dehydration starts when the body cannot replace fluid fast enough ^[1,5]. The body may also lose key salts, such as sodium and potassium ^[10].

These salts are called electrolytes. They help the body’s cells and organs work as they should ^[3,4]. A lack of fluid and electrolytes can harm the kidneys and other organs ^[3,4].

Dehydration may also affect blood flow and brain function ^[3]. Severe fluid loss can lead to shock ^[3,9]. Shock is a life-threatening problem caused by poor blood flow to the organs.

Mild, moderate, and severe dehydration

Dehydration may be mild, moderate, or severe ^[2,7]. These levels reflect how much fluid was lost or not replaced ^[2,7].

Mild dehydration often gets better when the person drinks more fluid ^[5,6]. Some moderate cases need fluids through a vein ^[8]. These are called intravenous or IV fluids.

Severe dehydration is a life-threatening emergency ^[2,7]. It needs medical treatment right away ^[2,5].

It may be hard to judge the level of dehydration at home. A health professional may look at symptoms, age, and recent fluid loss ^[3,4]. The person’s ability to drink also helps guide treatment ^[4].

People at higher risk

Babies and young children can become dehydrated during vomiting or diarrhea ^[5]. They rely on adults to notice the signs and offer fluids.

Older adults also have a higher risk ^[2,3,5]. They start with less water in their bodies than younger adults ^[5]. Some also take medicines that raise fluid loss ^[5].

Other high-risk groups include:

• People with diabetes or other long-term illnesses ^[2,3].
• People who take diuretics, also called water pills ^[2,5].
• Athletes who exercise in hot weather ^[2,9].
• Outdoor workers who spend long periods in heat ^[9,10].
• People who feel too sick or sick to their stomach to drink ^[2].
• People with a sore throat or mouth sores ^[2].

Knowing dehydration symptoms, causes, treatment and emergency warning signs can help people act early. This is vital for anyone at higher risk.

Symptoms by Severity and Age

Dehydration symptoms can range from mild thirst to shock ^[3]. The signs may vary by age and by the amount of fluid lost ^[3,4].

Early and mild-to-moderate symptoms

Common early symptoms may include:

• Thirst ^[6,8].
• A dry mouth or tongue ^[8].
• Headache ^[6,8].
• Tiredness ^[6,8].
• Dizziness or feeling faint ^[6,8].
• Weakness ^[3].
• Dark urine ^[7].
• Urinating less than usual ^[7].

Thirst is often an early signal that the body needs fluid ^[8]. Yet a person may already have mild dehydration when thirst starts ^[6].

Urine can offer useful clues. Dark urine or less urine may occur with mild or moderate dehydration ^[7]. These changes do not prove dehydration on their own.

Older adults may not feel strong thirst as fluid levels fall ^[2,3]. For this reason, thirst alone is not a good early warning sign for them ^[2,3].

Signs of severe dehydration

Severe dehydration can affect the brain and blood flow ^[3]. It may lead to organ damage or shock without fast treatment ^[3,9].

Signs of severe dehydration may include:

• Confusion or a sudden change in awareness ^[3].
• Fainting or loss of consciousness ^[3].
• Very little or no urine ^[2,7].
• Fast breathing ^[2,7].
• A fast pulse ^[2,7].
• Severe weakness ^[3].
• Collapse or poor response ^[3,9].
• Other signs of shock ^[3,9].

Confusion, fainting, very low urine output, fast breathing, and a fast pulse are serious warning signs ^[2,3,7]. Shock can mean that dehydration has become life-threatening ^[3,9].

Dehydration may also occur with heatstroke ^[6,10]. Heatstroke is a life-threatening illness caused by heat ^[10]. Suspected heatstroke needs emergency care ^[10].

Symptoms in babies and children

Babies and young children may not be able to describe how they feel. Adults must watch their drinking, actions, and urine output.

Signs in babies and children may include:

• Fewer wet diapers than normal ^[5].
• No tears when crying ^[5].
• A dry mouth or tongue ^[5].
• Unusual sleepiness ^[5].
• Low energy ^[5].
• A sunken soft spot on an infant’s head ^[5].
• Irritability ^[5].
• Poor drinking ^[5].

Vomiting and diarrhea are common causes of dehydration in young children ^[5]. Risk rises if a child cannot replace the lost fluid ^[4,5].

A change in body weight can help assess dehydration in a child ^[4]. A health professional may compare the child’s current and recent weights ^[4].

Prompt advice is important when a child cannot keep fluids down. It is also important if signs get worse or fluid loss continues.

Symptoms in older adults

Older adults may have a weaker thirst response ^[2,3]. This makes thirst an unreliable early sign of dehydration ^[2,3].

Their risk may also rise due to lower body water levels ^[5]. Illnesses and medicines can add to this risk ^[3,5].

Caregivers can watch for weakness, less urine, or changes in awareness ^[3,7]. They should not wait for the person to report thirst ^[2,3].

Causes and Risk Factors

Dehydration may come from fluid loss, low fluid intake, or both [1-3]. More than one cause may be present.

Illness-related fluid loss

Vomiting and diarrhea can cause a large loss of body fluid ^[1,2]. They can also remove key salts, such as sodium and potassium ^[10].

Fever can also cause dehydration ^[1,2,10]. At the same time, illness may make a person less willing to drink ^[2].

Nausea can reduce fluid intake ^[2]. So can a sore throat, mouth sores, or poor appetite during illness ^[2].

Young children face added risk from vomiting and diarrhea ^[5]. Adults should watch their urine, fluid intake, and level of awareness.

Heat, exercise, and inadequate intake

Heavy sweating is a common cause of dehydration ^[1,2]. Exercise in hot weather can cause even greater fluid loss ^[2,5,9].

Hot weather can cause dehydration when a person does not drink enough ^[5]. This can happen even without hard exercise ^[5].

People active in high heat often need more fluid ^[9]. Drinking before strong thirst starts may help prevent mild dehydration ^[6].

Travel or limited access to drinks may lead to low intake. People who rely on others for drinks may need extra support.

Long sun or heat exposure can lead to dangerous heat illness ^[10]. Dehydration and heatstroke can both be life-threatening without treatment ^[10].

Medicines and medical conditions

Frequent urination can cause dehydration ^[1,2]. Uncontrolled diabetes may cause a person to urinate too much ^[2,7].

Some medicines can also increase urine output ^[1,2]. Diuretics are one example ^[2,7]. These medicines help the body remove water through urine.

Long-term health problems may raise dehydration risk ^[3]. Diabetes and kidney problems are examples ^[2,3].

Some health problems reduce the wish or ability to drink. Examples include:

• Nausea ^[2].
• A sore throat ^[2].
• Mouth sores ^[2].
• Feeling too ill to eat or drink ^[2].
• Memory or thinking problems ^[3].
• Trouble reaching or preparing a drink.

These barriers are more serious when fluid loss is also high. Caregivers may need to offer drinks often and keep them close by.

Treatment and Diagnosis

Treatment replaces the fluid and electrolytes that the body has lost ^[4]. The best treatment depends on age, cause, and severity ^[4].

Home care for mild dehydration

Mild dehydration can often be treated by drinking fluids ^[5,6]. Small, frequent sips may be easier during vomiting or nausea.

Water may help with mild fluid loss when a person can drink normally. An oral rehydration solution may be better after vomiting or diarrhea ^[4,10].

An oral rehydration solution is a drink made to replace water and electrolytes ^[4]. It can replace salts lost through vomiting or diarrhea ^[4,10]. These solutions are often used for babies and children with these illnesses ^[4].

Use a prepared oral rehydration product as directed. Keep watching the person’s symptoms and urine output during home care.

Get medical advice if the person cannot keep fluids down. Help is also needed if fluid loss continues or symptoms get worse.

Do not force a drink into someone who is confused or not fully awake. A person who cannot swallow safely should not receive oral fluids.

When medical treatment is needed

Some moderate cases need IV fluids ^[8]. IV fluids enter the body through a vein.

Severe dehydration needs urgent medical treatment ^[2,7]. It may require IV fluid and electrolyte replacement ^[2,4,7].

Health professionals also treat the cause of fluid loss ^[3,4]. Causes may include vomiting, diarrhea, fever, or frequent urination [1-4]. Heat-related illness may also need urgent care ^[10].

Do not delay emergency care to keep trying home treatment. Confusion, collapse, or shock can mean oral fluids are not enough ^[3,9].

How clinicians assess dehydration

A health professional may start by asking about symptoms ^[4]. The person may also receive a physical exam ^[4].

No single symptom or test proves every case. Clinicians use several findings to judge the person’s condition ^[3,4].

Weight change may support a dehydration assessment in children ^[4]. A recent weight from before the illness can help with comparison ^[4].

Blood tests may check:

• Sodium levels ^[4].
• Potassium levels ^[4].
• Kidney function ^[4].

A urinalysis is a test of the urine. It can support a dehydration assessment and show how severe it may be ^[4]. It may also help check for a bladder infection ^[4].

The test results are reviewed with the person’s signs and history ^[3,4]. This full review helps guide the type of treatment ^[3,4].

When to See a Doctor: Emergency Warning Signs and Prevention

When dehydration is an emergency

Seek emergency care for:

• Confusion or a major change in awareness ^[3].
• Loss of consciousness ^[3].
• An inability to wake the person ^[3].
• Fainting or collapse ^[3].
• Severe weakness ^[3].
• Very little or no urine ^[2,7].
• Fast breathing ^[2,7].
• A fast pulse ^[2,7].
• Signs of shock ^[3,9].
• Suspected heatstroke ^[10].

Severe dehydration is a life-threatening emergency ^[2,7]. It can cause brain problems and shock ^[3].

Do not delay urgent care while trying to give drinks. This is vital if the person is confused or poorly responsive. Do not give oral fluids to someone who cannot swallow safely.

When to contact a healthcare professional

Get prompt medical advice for:

• Vomiting or diarrhea that does not stop.
• An inability to keep fluids down.
• Symptoms that get worse after oral fluids.
• Reduced urination that does not improve.
• Signs of dehydration in a baby or young child.
• Signs of dehydration in an older adult.
• Dehydration in someone with a long-term illness ^[3,5].
• Symptoms linked to a medicine that raises urine output ^[1,2].

Vomiting, diarrhea, fever, and frequent urination can cause major fluid loss ^[1,2]. Early help is vital for people at higher risk ^[3,5].

Practical dehydration prevention

Drink fluids often instead of waiting for strong thirst. This is very important for older adults ^[2,3]. Their thirst response may not warn them early enough ^[2,3].

Increase fluid intake during hot weather or exercise ^[5,9]. Drink more when heavy sweating occurs ^[1,2]. Plan for access to drinks before outdoor work or travel.

Other useful steps include:

• Keep drinks easy to reach.
• Offer children fluids often during illness.
• Track wet diapers in babies.
• Watch for less urine or darker urine ^[7].
• Offer older adults drinks on a regular plan.
• Replace fluid lost during vomiting, diarrhea, or fever ^[1,2].
• Use oral rehydration solution when fluid and salts are lost ^[4,10].
• Arrange help for people who cannot get drinks on their own.

Prevention should fit the person’s age and health needs. People with long-term illnesses may need advice from their care team.

Conclusion

Early action may stop dehydration from becoming severe. Many mild cases improve with oral fluids ^[5,6].

An oral rehydration solution replaces both fluid and electrolytes ^[4]. It may help replace losses from vomiting or diarrhea ^[4,10].

Moderate dehydration may need IV fluids ^[8]. Severe dehydration needs urgent medical treatment and IV replacement may be required ^[2,4,7].

Confusion, fainting, very little urine, fast breathing, and a fast pulse are emergency warning signs ^[2,3,7]. Shock, altered awareness, or suspected heatstroke also need emergency care ^[3,10].

Do not rely on home treatment when these severe signs appear. Seek immediate medical help.