A sudden run of watery nappies can be unsettling, especially when your baby is too young to tell you how they feel. Baby diarrhoea is often caused by a short-lived stomach infection, but the main concern is how quickly a little one can lose fluid. Knowing what is normal, what dehydration looks like and when to get help makes those first hours easier to manage.
Is it diarrhoea or just normal baby poo?
Baby stools vary enormously. Breastfed babies often have soft, loose, yellow stools and may poo after many feeds. Formula-fed babies usually have somewhat firmer stools. A loose stools baby concern is therefore best judged against your child’s usual pattern, rather than against what adult poo looks like.
Diarrhoea means a noticeable change to more frequent, watery stools. Nappies may suddenly soak up liquid poo or leak more than usual. A single soft nappy, particularly in an otherwise happy, feeding baby, does not automatically mean illness.
What causes diarrhoea in babies?
Stomach bugs
A viral stomach infection, or gastroenteritis, is a common reason for diarrhoea in babies. A baby stomach bug may also bring vomiting, a temperature, reduced appetite and unsettled sleep. The infection spreads easily through contaminated hands and surfaces, particularly where nappies are changed.
Other possible triggers
Medicines such as antibiotics can change bowel habits. Food allergies or intolerances may also contribute, although they do not explain every runny nappy. If symptoms recur alongside feeding problems, eczema, blood in the stool or poor weight gain, discuss the pattern with your GP rather than changing milk independently.
Why dehydration matters more than the number of nappies
Every watery stool carries away water and salts. Vomiting can increase those losses while making it harder to replace them. Babies under one year, especially those under six months, have a higher risk of dehydration. The danger is not simply how many times they poo; it is whether they can keep taking in enough fluid.
Signs of dehydration to watch for
Check for fewer wet nappies than usual, a dry mouth, few tears when crying, sunken eyes or a sunken soft spot on the head. A baby who seems unusually irritable, drowsy or less responsive may also be dehydrated. Very watery stools can make it difficult to tell whether a nappy also contains urine.
If your baby has signs of dehydration, seek an urgent GP appointment or call NHS 111. Cold skin, marked pallor, rapid breathing, difficulty waking or reduced responsiveness can indicate a medical emergency.
A useful nappy-and-feeds check
Imagine your six-month-old has four unusually watery nappies before lunchtime. Instead of trying to diagnose the cause from stool colour alone, note when each watery stool occurred, when they last had a clearly wet nappy and how much milk they have taken. If vomiting begins, record that too. This timeline gives NHS 111 or your GP more useful information than simply saying they have had a bad tummy.
What to do at home if your baby is otherwise well
Continue breastfeeding or offering your baby’s usual formula. If they are vomiting, smaller feeds offered more frequently may be easier to manage. Never dilute formula: prepare it at its normal strength. For a baby on formula or solid foods, the NHS also advises small sips of water between feeds; water for babies under six months should first be boiled and cooled.
Oral rehydration solution, often called ORS, replaces fluid and salts lost through diarrhoea. A pharmacist or healthcare professional can advise which preparation is suitable and how to use it. Mix sachets exactly as instructed. If dehydration is suspected, get medical advice promptly rather than relying on home treatment alone. If your baby repeatedly vomits fluids or refuses feeds, seek urgent help.
If your baby eats solids and is not dehydrated, you can generally continue familiar age-appropriate foods as tolerated. During treatment for diagnosed dehydration, follow the clinician’s specific feeding advice. Avoid fruit juice and fizzy drinks, which can worsen diarrhoea, and do not give anti-diarrhoea medicine to a baby.
For related guidance, read about signs of dehydration in babies and what to do when your baby is vomiting. These symptoms often occur together, but the best response depends on your baby’s age and overall condition.
When should you contact a healthcare professional?
Call NHS 111 if you are worried about a baby under 12 months, if they stop breast or bottle feeding, have fewer wet nappies, cannot keep fluids down, have blood in their diarrhoea or have diarrhoea lasting more than seven days. An urgent GP assessment is also appropriate when dehydration is suspected or your baby is getting worse rather than better.
A temperature of 38°C or higher in a baby under three months needs urgent medical assessment. For babies aged three to six months, a temperature of 39°C or higher is also a reason to seek urgent advice. Trust changes in behaviour as well as the thermometer: an unusually floppy, difficult-to-wake baby needs immediate attention.
Call 999 or go to A&E for a baby who is unresponsive, struggling to breathe, has blue, grey or markedly blotchy skin, severe sudden tummy pain, or green vomit. Those symptoms require emergency assessment, even if diarrhoea appears mild.
How long does baby diarrhoea usually last?
With gastroenteritis, diarrhoea commonly lasts five to seven days, although it can take up to two weeks to resolve completely. Vomiting often improves sooner, usually within one or two days. The important trend is that your baby continues feeding, produces wet nappies and seems increasingly like themselves.
Wash your hands with soap and water after every nappy change, clean frequently touched surfaces and wash soiled fabrics separately. Keep your baby away from nursery or childcare until at least 48 hours after the last episode of diarrhoea or vomiting. Our guide to managing common baby stomach bugs can help with reducing spread around the family.
Frequently asked questions
Can a breastfed baby have diarrhoea?
Yes. Breastfed poo is naturally loose, but a sudden increase in very watery stools, particularly with vomiting or poor feeding, can suggest diarrhoea. Compare the change with your baby’s usual nappies.
Should I stop giving milk during diarrhoea?
No. Continue breastfeeds or normal-strength formula unless a healthcare professional specifically advises otherwise. Milk feeds provide valuable fluid and nutrition during recovery.
Is green baby poo a sign of infection?
Not necessarily. Stool colour can vary with feeding and digestion. A persistent change accompanied by frequent watery stools, blood, poor feeding or illness deserves medical advice. Green vomit is different: it needs emergency assessment.
When is diarrhoea dehydration an emergency?
Seek urgent advice for fewer wet nappies, a sunken soft spot, very few tears or unusual drowsiness. Call 999 for severe breathing problems, unresponsiveness or signs of shock, such as cold, pale or blotchy skin.
Helping your baby recover safely
Most episodes of baby diarrhoea improve with time and careful attention to fluids. Keep offering usual milk feeds, watch wet nappies and pay attention to changes in alertness. If something does not feel right, especially with a younger baby, contact NHS 111 or your GP early. Recognising dehydration and acting promptly matters far more than trying to stop every loose stool.