Dehydration

Overview

Dehydration happens when your body loses more fluid than it takes in. This means your body doesn't have enough water and other fluids to work properly. Even mild dehydration can make you feel tired, thirsty, and dizzy. Severe dehydration needs urgent medical care.

Yes, dehydration is very common. Many people experience mild dehydration at some point, especially during hot weather, after exercise, or when ill with vomiting or diarrhoea.

Dehydration can affect anyone, but it is more common in babies, young children, older adults, and people with chronic health conditions like diabetes or kidney disease. People who exercise intensely, work outdoors in the heat, or cannot get enough fluids are also at higher risk.

Symptoms

Common symptoms

• Thirst
• Dry mouth, lips, and eyes
• Dark yellow or strong-smelling urine
• Passing urine less often than usual
• Feeling tired or sleepy
• Headache
• Dizziness or lightheadedness

Symptoms in children

• Dry mouth and tongue
• No tears when crying
• Few wet nappies (less than 6 in 24 hours)
• Sunken eyes or cheeks
• Sunken soft spot on the top of the head (fontanelle)
• Irritability or listlessness (low energy)

Symptoms in older adults

• Confusion or memory problems
• Dizziness or falls
• Dry skin that stays 'tented' when pinched
• Less frequent urination
• Dark urine
• Low blood pressure

Causes

Main causes

• Not drinking enough water or other fluids
• Vomiting or diarrhoea from illness (like stomach flu or food poisoning)
• Excessive sweating from exercise or hot weather
• Fever that increases fluid loss
• Conditions that increase urination, such as uncontrolled diabetes or certain medications

Risk factors

• Being very young (babies and young children)
• Being older (over 65 years)
• Living in a hot or humid climate
• Exercising intensely without drinking enough
• Having a chronic illness like kidney disease or diabetes
• Taking diuretics ('water pills') or other medications that increase urination
• Being unable to access or drink fluids (e.g., during illness or confusion)

When to see a doctor

See a doctor urgently if:

• You or your child has emergency symptoms listed above
• You cannot keep fluids down due to vomiting or diarrhoea for more than 24 hours
• You have signs of severe dehydration (confusion, rapid heart rate, no urine for 8 hours)

Book a routine appointment if:

• You have mild dehydration that does not improve with drinking fluids after 24 hours
• You have ongoing diarrhoea or vomiting that lasts more than 2 days in adults
• You are concerned about dehydration due to a chronic condition (e.g., diabetes or kidney disease)

Diagnosis

Doctors diagnose dehydration by asking about your symptoms, checking your vital signs (pulse, blood pressure, temperature), and doing a physical exam. They may look for signs like dry skin, dry mouth, and low blood pressure.

Tests that may be done

• Urine test: can check how concentrated your urine is (a sign of dehydration)
• Blood tests: measure electrolyte levels (like sodium and potassium) and kidney function

What to expect at your appointment

If you see a doctor for dehydration, they will quickly assess your level of dehydration. For mild cases, they may recommend drinking fluids at home. For more severe cases, they may give you fluids through a vein (intravenous or IV) to rehydrate you faster. This usually takes a few hours in a clinic or hospital.

Treatment

The main goal of treatment is to replace the fluid and electrolytes (salts) your body has lost. For mild dehydration, drinking water or an oral rehydration solution (a mix of water, sugar, and salt) is usually enough. For moderate to severe dehydration, medical treatment with IV fluids may be needed. Most people recover fully within hours to a day.

Self-care at home

• Drink small amounts of water frequently – a few sips every 5 to 10 minutes – especially if you are nauseous.
• Use an oral rehydration solution (available from pharmacies) – these are better than plain water if you have lost salts through vomiting or diarrhoea.
• Avoid drinks that can make dehydration worse, such as alcohol, coffee, tea, or sugary fizzy drinks.
• Rest and stay in a cool place if you feel dizzy or overheated.
• For children with diarrhoea, continue breastfeeding or formula feeding, and offer oral rehydration solution between feeds as directed.

Medical treatments

If you are moderately or severely dehydrated, or cannot keep fluids down, a healthcare provider may give you fluids directly into a vein (intravenous infusion). This quickly restores your body's fluid and electrolyte balance. In hospital, they will also treat the underlying cause, such as infection or vomiting. They monitor your response and adjust treatment as needed.

When is surgery considered?

Surgery is not a treatment for dehydration. However, if dehydration leads to complications (like kidney failure or electrolyte imbalance), you may need further medical care, but surgery is rarely needed.

Living with this condition

Most people recover from dehydration without any long-term effects. After an episode, continue drinking plenty of fluids throughout the day. Pay attention to your thirst and urine colour – pale yellow means you are well-hydrated. If you have a condition that increases your risk (like diabetes or kidney disease), work with your doctor to manage it.

Lifestyle tips

• Carry a water bottle with you and sip throughout the day.
• Set reminders to drink if you often forget.
• Eat water-rich foods like fruits (watermelon, oranges) and vegetables (cucumber, lettuce).
• Drink extra fluids before, during, and after exercise.
• In hot weather or when sick, increase your fluid intake.

Diet and exercise

A balanced diet with plenty of fruits and vegetables helps maintain hydration. During exercise, drink water before you feel thirsty. For prolonged or intense exercise, a sports drink (with electrolytes) may help, but water is fine for most activities. Avoid heavy meals and caffeine before exercise, as they can dehydrate you.

Mental health and emotional wellbeing

Severe dehydration can cause confusion and irritability, which can be distressing. If you or a loved one experiences confusion during dehydration, seek medical help. Once rehydrated, mood and thinking usually return to normal. If you feel anxious about getting dehydrated again, talk to your doctor – they can help you create a plan to stay hydrated safely.

Prevention

Yes, in most cases dehydration can be prevented by drinking enough fluids every day, especially in hot weather, during illness, or when exercising. Listen to your body – thirst is a sign you already need fluid. Aim for pale yellow urine as a sign of good hydration.

Vaccines

There is no vaccine for dehydration. However, vaccines can prevent illnesses (like diarrhoea from rotavirus) that can lead to dehydration. Talk to your doctor about recommended vaccines for you and your family.

Screening programmes

Routine screening for dehydration is not needed for most people. However, if you have a chronic condition or are at high risk, your doctor may check your hydration status during regular appointments. For older adults or people in care homes, staff may monitor urine output and offer fluids regularly.

Complications

If left untreated

• Urinary tract infections and kidney stones from concentrated urine
• Heat cramps, heat exhaustion, or heat stroke from overheating
• Low blood volume (hypovolaemia) that can lead to fainting or shock
• Seizures from electrolyte imbalances (especially low sodium or potassium)
• Kidney failure in severe or prolonged cases

Long-term outlook

With prompt treatment, most people recover completely from dehydration within a day. Even severe dehydration has a good outlook when treated quickly. The key is to notice the early signs and act – drinking fluids or seeking medical help when needed. By staying aware, you can prevent most complications and stay healthy.

Find support

International organisations

• World Health Organization (WHO) – Dehydration Management ↗

Local organisations

• NHS – Dehydration ↗ · UK
• CDC – Tips for Preventing Heat-Related Illness ↗ · USA
• Health Direct – Dehydration ↗ · Australia

Helplines

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