Vomiting and Diarrhoea: Rehydration Is the Whole Job — and How to Spot Dehydration

Acute gastroenteritis is one of the most common childhood emergencies. Most cases are viral and self-limiting — the danger isn't the virus, it's dehydration. So the entire job of home care is one thing: getting fluid and electrolytes back in.

Rehydration: the method matters more than the fluid

What to use: oral rehydration solution (ORS) is first choice — its salt-to-sugar ratio is optimised for absorption.

❌ What not to use: sports drinks (too much sugar, wrong electrolyte balance), plain water alone (dilutes electrolytes in volume), and sugary juice or fizzy drinks (hyperosmolar — they worsen diarrhoea).

How to give it — this is the critical part:

Small and often: 5–10ml at a time, every 5 minutes.

Give a vomiting child a full cup and it will almost certainly come straight back up. Use a spoon or an oral syringe so the stomach can tolerate and absorb it. After a vomit, pause 10 minutes, then restart small.

Keeping this rhythm through the night is often what prevents a trip to the drip.

About food

Don't withhold food. The old "rest the gut" advice has been overturned — resuming normal feeding early shortens the illness and limits weight loss.

Breast milk or formula: keep going, no dilution needed
On solids: offer what they'll take, favouring easily digested foods (rice, noodles, banana, potato), low in fat and sugar
Avoid: sugary drinks, greasy food, and large amounts of dairy (some children get temporary lactose intolerance during the acute phase)

Grading dehydration

Mild (manage at home): slightly dry lips, marginally less urine, generally alert.

Moderate (see a doctor): clearly dry mouth, markedly reduced urine (over 6 hours dry in an infant), few tears when crying, slightly sunken eyes or fontanelle, low energy, reduced skin elasticity.

Severe (emergency, go now): no urine, clearly sunken eyes, skin that stays tented when pinched, drowsy and hard to rouse, rapid breathing, cold mottled extremities.

A practical home metric: track the nappies. Over 6 hours dry in an infant, or 8 in a toddler, means hospital.

Other reasons to seek care

Vomit containing blood or dark green bile
Blood or redcurrant-jelly appearance in stool
Severe persistent abdominal pain, distension, or guarding the belly
Persistent high fever, lethargy or seizures
Any vomiting and diarrhoea in a baby under 3 months
Vomiting beyond 24 hours with nothing staying down, or diarrhoea beyond 7 days

Three things not to do

❌ Don't give anti-diarrhoeal medicines on your own: agents like loperamide carry serious risks in young children, and diarrhoea is how the pathogen leaves
❌ Don't self-prescribe antibiotics: most acute gastroenteritis is viral — antibiotics don't help and damage gut flora
❌ Don't fast them: proven to prolong the illness

Limiting spread

Rotavirus and norovirus are extremely contagious. Handwashing is the key control — soap and running water, since alcohol gels work poorly against norovirus. Clean vomit-contaminated surfaces with a chlorine-based product, wash their utensils separately, and keep children home for 48 hours after symptoms stop. Rotavirus vaccination effectively prevents severe disease.

Compiled from mainstream paediatric gastroenteritis guidance. Not medical advice — dehydration progresses quickly in small children, so seek care when in doubt.