Dehydration happens when your body loses more fluid than it takes in, through sweating, diarrhoea, vomiting, fever or simply not drinking enough. Babies, young children and older adults become dehydrated fastest, and severe dehydration can be life-threatening.
A child with diarrhoea who is still playing and drinking is very different from one who is floppy with no tears. Knowing the signs means you will know which one needs a clinic today.
Signs in adults
- Feeling thirsty
- Dark yellow, strong-smelling urine
- Passing urine less often
- Dry mouth, lips and eyes
- Headache, tiredness and dizziness, especially on standing
- Muscle cramps
Signs in babies and young children
- Fewer wet nappies (for example, none in 6 hours or more)
- A sunken soft spot (fontanelle) on top of the head
- Few or no tears when crying
- Dry mouth
- Unusually sleepy, floppy or irritable
- Cold hands and feet
Get urgent help if a baby or child is very drowsy, floppy or hard to wake, has not passed urine for 12 hours, has sunken eyes, or is breathing fast. In adults, seek urgent care for confusion, fainting, a very fast heartbeat or no urine all day.
Why oral rehydration solution works
When you lose fluid through diarrhoea or vomiting, you also lose salts. Oral rehydration solution (ORS) contains the right balance of salt and sugar so the gut absorbs water faster than plain water alone. The World Health Organization credits ORS with saving millions of children’s lives.
- Use ready-made sachets from a pharmacy and mix exactly as instructed
- Give small, frequent sips, especially if vomiting: a spoonful every minute for a child
- Keep breastfeeding babies
- Avoid sugary fizzy drinks and undiluted juice, which can make diarrhoea worse
Who is most at risk?
- Babies and young children
- Older adults, who may not feel thirsty
- People with diabetes or kidney disease
- People taking diuretics
- Anyone with diarrhoea and vomiting, fever, or working in heat
How much should you drink?
Needs vary with climate, activity and health. Pale yellow urine is a simple sign you are drinking enough. See our guide to how much water you need.
“But surely plain water is enough to rehydrate?”
For mild thirst, yes. But diarrhoea and vomiting also drain salts. Oral rehydration solution replaces both and is absorbed faster, which is why it has saved millions of children’s lives.
Your next step: keep a few ORS sachets in your home first aid kit, and share this guide with new parents.
Related: Heat exhaustion vs heat stroke
Sources: World Health Organization, diarrhoeal disease fact sheet and oral rehydration salts guidance; NHS dehydration advice; NICE guideline CG84, diarrhoea and vomiting in children.
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