Baby diarrhea: causes, warning signs and what to do
Diarrhea is one of the more unsettling things to deal with in a young baby, and it can be hard to know straight away whether what you are seeing is something to worry about or simply a phase that will pass on its own. The good news is that most cases in babies are caused by a short-lived viral infection and resolve within a week, without any special treatment. Understanding what diarrhea actually looks like in babies, what to watch for, and exactly when to get help will make the whole experience easier to navigate.
What counts as diarrhea in babies?
This is one of the most common points of confusion, and for good reason: the range of what is "normal" for baby stools is enormous, and what looks alarming to a new parent is often completely fine.
Diarrhea in a baby does not mean a certain number of dirty nappies per day. It means a sudden change from what is normal for your baby. Specifically, stools that are more frequent than usual, looser or more watery than usual, and often more foul-smelling than usual.
Breastfed babies can naturally have very soft, runny, or even liquid-looking stools, often described as mustard yellow and slightly seedy. Some breastfed babies produce a dirty nappy after every feed, while others may go several days without one. Both ends of this range are normal. Runny, frequent stools in a breastfed baby who has always had runny, frequent stools are not diarrhea.
Formula-fed babies tend to produce firmer, less frequent stools that are typically pale yellow to tan in colour. Their normal range is narrower than that of breastfed babies.
In both cases, what matters is the change from your baby's established pattern. If your baby normally has two nappies a day and suddenly has six, and the stools are much more watery than usual, that is diarrhea. If your breastfed baby has always had five runny nappies a day and nothing has changed, that is not.
Common causes of diarrhea in babies
Knowing what might be behind your baby's diarrhea can help you work out how concerned to be and what to expect.
Viral gastroenteritis is the most common cause by far. Viruses such as rotavirus and norovirus cause inflammation of the gut, leading to diarrhea, and often vomiting as well. These infections are very common in babies and young children and usually resolve on their own within five to seven days. Rotavirus vaccination, offered routinely in the UK and many other countries, significantly reduces the risk of severe rotavirus illness.
Antibiotic side effects are another frequent cause. Antibiotics work by killing bacteria, but they do not distinguish between harmful bacteria and the helpful bacteria that live in the gut. Disrupting this balance often causes loose stools for the duration of the antibiotic course and sometimes for a short time after.
Dietary changes can loosen stools, particularly when a baby starts on solid foods, when a new food is introduced too quickly, or when a baby has too much fruit or fruit juice. High-sugar drinks can draw extra water into the gut and speed up digestion.
Food intolerance or cow's milk protein allergy can cause persistent or recurring loose stools, often with other symptoms such as skin rashes or excessive wind. This is worth raising with your GP if diarrhea keeps coming back without an obvious cause.
Teething is often blamed for diarrhea, and many parents notice loose stools around the time their baby is cutting a tooth. The NHS notes that teething does not directly cause diarrhea. However, extra saliva production, chewing on objects, and generally putting more things in the mouth during teething may play a role. If your baby has loose stools during teething, monitor them as you normally would and seek advice if it persists.
Bacterial infections are less common in the UK and other high-income settings, but can occur from contaminated food or water. Bacterial gastroenteritis sometimes produces blood or mucus in the stool, which is always a reason to contact your GP.
How to care for your baby at home
For most cases of diarrhea in a baby who is otherwise well and showing no signs of dehydration, good home care is all that is needed.
Continue breastfeeding. If you are breastfeeding, carry on and offer the breast more frequently than usual. Breast milk contains antibodies that actively help your baby fight the infection, and it is easy to digest. There is no reason to stop or reduce breastfeeds.
Continue formula feeds as normal. If your baby is formula-fed, continue offering their usual formula at the usual concentration. Do not dilute formula. A common instinct is to make formula weaker during illness, but this reduces the nutrition your baby receives and can make dehydration more likely rather than less.
For older babies on solids, continue to offer their usual foods in small amounts, often. Appetite may be reduced during illness and that is fine. Avoid fruit juice, sports drinks, or any sugary drink, as these can make diarrhea worse.
Extra fluids for babies over six months. For babies who have started solids, small sips of water between feeds can help keep them hydrated, particularly if the weather is warm.
Good hygiene. Wash your hands thoroughly with soap and water after every nappy change, before preparing food, and before feeding your baby. Change nappies on a surface that can be wiped clean. This is especially important with viral gastroenteritis, which spreads very easily.
There are also a few things you should not do. Do not give anti-diarrhoea medicines to babies or children: they are not safe for children under 12. Do not give fruit juice or sports drinks. Do not dilute formula. And do not stop feeds in an attempt to rest the gut: keeping up feeds is the most important thing you can do to prevent dehydration.
Watching for dehydration
Dehydration is the main risk when a baby has diarrhea, and it is worth understanding what to look for. Babies can lose fluids quickly, and young babies have fewer reserves than older children or adults.
Signs of dehydration to watch for include:
- Fewer wet nappies than usual. A rough guide is fewer than four wet nappies in 24 hours.
- A dry mouth or lips.
- No tears when your baby cries.
- Sunken eyes, or a sunken fontanelle (the soft spot on top of your baby's head).
- Pale, mottled, or bluish-tinged skin.
- Unusual sleepiness, limpness, or difficulty waking.
- Refusing feeds.
Counting wet nappies is one of the most practical things you can do when your baby has diarrhea. Keeping a note of how many wet nappies your baby produces in each 24-hour period gives you and your doctor useful information, and it also helps you notice a downward trend early. You can log nappies in Cubby to stay on top of this without relying on memory.
If you notice signs of dehydration, contact your GP or call 111 promptly. Dehydration in young babies can worsen quickly and should not be left to monitor at home without advice.
When diarrhea needs medical attention
Most cases of baby diarrhea do not require a doctor visit. But some situations need prompt medical attention, and it is important to know what those are.
Contact your GP, call 111, or go to your nearest A&E department if:
- There is blood or mucus in your baby's stool.
- The diarrhea has lasted more than two weeks.
- Your baby has a high fever: above 38C if they are under three months old, or above 39C if they are older.
- Your baby is under three months old and has any diarrhea at all.
- You can see signs of dehydration, as described above.
- Your baby seems very unwell, is unusually floppy or difficult to rouse, or you are worried for any reason.
Trust your instincts. You know your baby. If something feels wrong, get help. It is always better to call and be reassured than to wait when you are unsure.
Oral rehydration salts
If your baby shows signs of dehydration, a doctor or pharmacist may recommend oral rehydration salts (ORS). In the UK, Dioralyte is the most widely used brand. ORS sachets contain a precise balance of salts, sugars, and water that help the gut absorb fluids more effectively than plain water alone.
ORS should be used on medical advice, not as a first-line home treatment. If a doctor or pharmacist recommends them, give small, frequent sips rather than large amounts at once. Giving too much too quickly can cause vomiting.
Oral rehydration salts are not a substitute for continuing feeds. Breastfeeds and formula feeds should continue alongside ORS, as your baby still needs the nutrition they provide.
When it passes and what to expect
Viral gastroenteritis, the most common cause of diarrhea in babies, usually resolves within five to seven days. The worst of it is often over by day three or four, and stools gradually firm up over the following days.
It is common for stools to remain softer than usual for a couple of weeks after an episode of gastroenteritis, even once your baby is clearly recovering and feeding normally. This is not a sign that something is still wrong. The gut lining needs a little time to fully recover.
You may have heard of the BRAT diet (bananas, rice, applesauce, toast) as a remedy for diarrhea. Neither the NHS nor the AAP (American Academy of Pediatrics) recommends the BRAT diet for babies or children. There is no proven benefit, and restricting your baby to these foods during illness reduces the nutrition available at a time when the body needs it most. Offer your baby their normal foods in small, frequent amounts and let their appetite guide you.
Frequently asked questions
How many dirty nappies counts as diarrhea?
There is no single number, because normal stool frequency varies enormously between babies. A breastfed newborn may produce a dirty nappy after every feed, while another baby of the same age may go several days between nappies. Diarrhea means a sudden change from what is normal for your baby: more frequent stools, looser or more watery consistency, and often a stronger smell. It is the change from your baby's own baseline that matters, not a fixed number.
Can teething cause diarrhea in babies?
The NHS states that teething does not directly cause diarrhea. However, many parents notice looser stools around the time teeth come through. This may be because babies produce more saliva during teething and swallow it, or because they chew on objects that carry bacteria. If your baby has loose stools while teething, keep an eye on them as you normally would. If the diarrhea is frequent, very watery, or lasts more than a day or two, contact your GP rather than assuming teething is the sole cause.
Should I stop formula feeds if my baby has diarrhea?
No. If your baby is formula-fed, continue their normal feeds as usual. Do not dilute formula, as this reduces the nutrition your baby receives and will not help clear the diarrhea faster. Stopping or diluting feeds can make dehydration more likely. The same applies to breastfeeding: continue to offer the breast and feed as often as your baby wants. Breast milk contains antibodies that help your baby fight infection and is easy to digest.
What are the signs of dehydration from diarrhea?
Signs of dehydration in a baby include fewer wet nappies than usual (fewer than four in 24 hours), a dry mouth, no tears when crying, sunken eyes or a sunken fontanelle (the soft spot on the top of the head), pale or mottled skin, unusual sleepiness or limpness, and refusing feeds. If you notice any of these signs, contact your GP or call 111 promptly. Dehydration in young babies can develop and worsen quickly.
Can I give anti-diarrhoea medicine to my baby?
No. Anti-diarrhoea medicines such as loperamide (Imodium) must not be given to children under 12 years old. They are not safe for babies and will not help. If you are concerned about your baby's symptoms, speak to your GP or pharmacist, who may recommend oral rehydration salts such as Dioralyte if your baby shows signs of dehydration.
When does baby diarrhea need a doctor?
Contact your GP, call 111, or go to A&E if your baby has blood or mucus in their stool; if the diarrhea has lasted more than two weeks; if your baby is under three months old and has any diarrhea; if your baby has a high fever (above 38C if under three months, above 39C in older babies); if you notice any signs of dehydration such as fewer wet nappies, dry mouth, sunken eyes, or unusual sleepiness; or if your baby seems very unwell or you are worried for any reason. Trust your instincts: if something feels wrong, get help.
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