Dehydration: learn first aid

Adult first aid for someone who may have dehydration including signs and symptoms to look out for, as well as steps to take in an emergency.

What is dehydration?

Dehydration occurs when fluid and essential salts are lost from the body and not replaced. Dehydration can be the result of excess sweating during sports activities or exposure to the sun or hot humid conditions.

Signs and symptoms of dehydration

Someone with dehydration might have been sweating a lot due to hot temperatures, exertion, illness or losing fluids from vomiting and diarrhoea.

They may have:

  • a dry mouth with dry or cracked lips
  • a headache or be dizzy and confused
  • darker urine
  • less frequent urination.

Babies and young children may have pallid skin and sunken eyes. Young babies may have a sunken fontanelle (the soft spot on the top of the head). Learn heat-related first aid treatment for babies and children.

First aid steps to help someone who is dehydrated

Step 1. Get them to rest.

Reassure the person and help them to sit down.

A woman wearing a red shirt helps another woman wearing a grey shirt across the room

Step 2. Give them plenty of fluids (not energy or fizzy drinks, or alcohol) to drink.

Drinking water will replace lost fluids. If you have them isotonic sports drinks will help replace salts lost through sweating.

Close-up shot of a woman drinking a glass of water

Step 3. If their condition gets worse, seek medical advice.

Close up shot of an iPhone with the numbers 999 dialled

More basic first aid learning for dehydration

When dehydration is not addressed, it can lead to other heat-related illnesses such as heat exhaustion and heatstroke. 

Learn the symptoms and basic first aid treatment for heat exhaustion and heatstroke so you can keep yourself and others safe during hot weather.

You can also test your knowledge with our heat exhaustion quiz in the British Red Cross free First aid app.

Or, learn first aid treatment and symptoms for heat exhaustion and heatstroke in babies and children.