Baby poo can be soft and runny, especially with breastfeeding. Diarrhoea is more likely when there is a clear change from your baby’s usual pattern, with unusually watery poos, often more frequently. The important questions are how your baby is feeding, whether they are passing urine and how well they seem.

A baby under 6 months with suspected gastro or diarrhoea should be checked by a doctor promptly. Young babies can lose fluid quickly. Do not wait for a set number of dirty nappies before asking for help.

When diarrhoea needs urgent care

A baby aged 3 months or younger with a temperature of 38°C or higher needs immediate emergency-department assessment. Call 000 if your baby is unresponsive, very difficult to wake, struggling to breathe or having a seizure for the first time.

Go to hospital urgently if your baby has signs of severe dehydration, cannot keep fluids down and is becoming dehydrated, or has green vomit. Seek prompt medical assessment for blood in the poo, persistent or severe tummy pain, poor feeding, a clear reduction in wet nappies or worsening illness. Do not assume these changes are simply teething or a routine tummy upset.

Our baby fever guide explains the age-based fever advice. If you are unsure about the urgency, call Healthdirect on 1800 022 222; emergency symptoms need 000 or emergency care without delay.

Normal poo and a change worth checking

The colour, texture and frequency of poo change with age and feeding. One loose nappy alone does not establish diarrhoea, and a normal pattern for one baby can be different from another’s. Look for a noticeable change together with how your baby is behaving and feeding.

Infection, often a virus, is a common cause of diarrhoea. Medicines or other conditions can also be involved. The cause cannot be worked out from colour alone, and antibiotics are not automatically needed. Let a clinician assess the pattern rather than changing medicines or formula yourself.

Pregnancy, Birth and Baby’s poo guide is useful for understanding the normal range.

Watch hydration closely

Diarrhoea and vomiting can remove more fluid than a baby is taking in. Notice:

• fewer wet nappies or less urine than usual
• a dry mouth or lips
• unusual quietness, low energy or increasing sleepiness
• sunken eyes, cold limbs or mottled skin, particularly with a baby who seems very unwell.

Severe dehydration needs urgent hospital care. Do not wait for every sign to appear. A young baby with poor intake or suspected dehydration needs professional advice even when the temperature is normal.

Feeds and fluids

Keep offering breastfeeds, usually more often. If you use formula, offer smaller, frequent feeds at the normal strength while arranging the advice your baby needs. Do not add extra water to formula.

Oral rehydration solution can replace lost fluid and salts, but a young baby’s plan should be guided by a clinician. If milk or other fluids are not staying down, ask for help promptly rather than repeatedly trying different drinks. A clinician may recommend a temporary oral-rehydration plan and explain when to resume usual feeds.

Do not give homemade salt-and-sugar mixtures, sports drinks or plain water as a substitute for a young baby’s milk feeds. Avoid guessing a fluid volume from advice intended for an older child. Babies who already eat solids can be offered their usual age-appropriate foods as tolerated; do not force food or impose a prolonged restrictive diet.

Do not give medicines to stop diarrhoea unless your baby’s doctor specifically recommends them. Speak to the prescriber if you suspect a medicine is contributing to the illness.

Protect the skin and reduce spread

Change soiled nappies promptly. Clean gently, pat the skin dry and use an appropriate barrier cream if needed. Our nappy-changing guide covers practical care.

Wash your hands with soap and water after changing nappies and before preparing food or feeds. Clean contaminated surfaces and avoid sharing towels. Follow your childcare service’s and local health advice about returning after vomiting or diarrhoea.

When to check back

Follow the clinician’s review plan. Seek help sooner if feeds or urine output drop, vomiting continues, blood appears, pain persists or your baby becomes more unwell. A general statement that gastro can last several days is not a reason to wait with a deteriorating baby.

Sources and further reading

• Royal Children’s Hospital: Gastroenteritis
• Royal Children’s Hospital: Dehydration in babies and children
• Royal Children’s Hospital: Gastroenteritis clinical guideline
• Pregnancy, Birth and Baby: Poos and wees
• Healthdirect: Fever in babies and children

General Australian health information. Babies with illness need advice suited to their age, feeding and medical history.