Signs of dehydration

Category: General & Whole-Body Symptoms · All general symptoms

What it can feel like

Dehydration means the body has lost more water than it has taken in. Early signs are thirst, a dry mouth, darker urine and passing urine less often; as it worsens there can be dizziness, a racing pulse, headache, confusion and, in babies, fewer wet nappies and a sunken soft spot.

Possible causes

A symptom can have many causes, and most are not serious. The lists below group conditions this symptom can be associated with — common causes first. They are possibilities to discuss with a clinician, not a diagnosis.

Common causes

Dehydration can be associated with vomiting and diarrhoea, fever, hot weather, hard exercise, alcohol, and not drinking enough during illness — a particular risk for older people who may not feel thirsty.

Other possible causes

Significant dehydration can develop with severe infections, uncontrolled diabetes, kidney problems, or medicines that increase urine output, and it can itself strain the kidneys and circulation if it is not corrected.

Red flags — when to seek help promptly

Being unable to keep any fluids down
Confusion, severe dizziness, fainting or a very fast heartbeat
Passing very little or no urine for many hours
A baby who is drowsy, has a sunken soft spot, or has had few wet nappies
Vomiting or diarrhoea with blood, or in someone frail or elderly

What a clinician may do

A clinician will check pulse, blood pressure (including on standing), skin and mouth dryness, and how much urine you are passing. Blood tests for kidney function and salts, and a urine test, show how severe it is; treatment is fluids by mouth or, if needed, a drip.

Watch: related videos

Examination and clinical videos from the MedicalVideos.com library relevant to this symptom. Some clinical footage is graphic — that is the nature of a medical video library.

▶ WatchSigns of dehydrationWatch on MedicalVideos.com

Related guides on MedicalVideos.com

Frequently asked questions

How can I tell if my child is dehydrated?

Watch for fewer wet nappies or trips to the toilet, a dry mouth, no tears when crying, unusual sleepiness and a sunken soft spot in babies. Trust your instinct — a child who is not drinking and is becoming drowsy needs same-day assessment.

Are sports drinks or oral rehydration better than water?

For mild dehydration from illness, oral rehydration solutions replace water and salts in the right balance and are a good choice, especially for children and older people. Water is fine for simple thirst after exercise or heat.

Related symptoms — General & Whole-Body Symptoms

Chills Excessive sweating Excessive thirst Fatigue Feeling cold all the time Feeling generally unwell (malaise)

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Please note: This page is educational information about a symptom. A symptom alone cannot diagnose any condition, and the causes listed here are possibilities, not a diagnosis. If you are worried about a symptom — especially one that is new, severe, getting worse or not going away — please see your own clinician, who can examine you and arrange tests. In an emergency, call your local emergency number.