Diarrhea in Babies: What’s Normal, What’s Not, and Why It Happens

Diarrhea is one of the most common reasons parents worry about their baby’s health. Loose, frequent stools can look alarming, particularly in very young babies, but in many cases diarrhea is short-lived and not a sign of serious illness.

Because infant bowel movements vary widely depending on age, feeding method, and diet, it can be difficult to know when diarrhea is normal and when it requires medical attention. In this article, we explain what diarrhea is, how to recognize it in babies, common causes, and when it’s important to see a doctor.

What is diarrhea?

Diarrhea is a medical term used to describe frequent, watery bowel movements. It may sometimes (but not always) contain mucus or blood and can have a foul smell.

Diarrhea can be acute, meaning it occurs suddenly and lasts for less than four weeks, or chronic, meaning it lasts longer than four weeks.

Diarrhea is not a condition in itself; it is a symptom of an underlying issue. There are many reasons why babies and children develop diarrhea. Most causes are not serious and will either resolve on their own or improve with simple dietary changes. Because many episodes of diarrhea are short-lived, the exact cause is not always identified.

How to tell if your baby has diarrhea

Infant stools are normally quite runny, especially when a baby is breastfed. Many babies will occasionally have one or several stools that are much looser, a different color, or a little more smelly than usual. Without other physical symptoms, loose watery bowel movements do not necessarily mean your baby is unwell.

Although changes in bowel habits can be related to a change in your baby’s diet (or a breastfeeding mother’s diet), diarrhea does not automatically mean a food or milk allergy or intolerance is involved. Babies may experience brief episodes of diarrhea from time to time for no identifiable reason.

If your baby is healthy, gaining weight well, and has plenty of wet diapers (six or more per day), frequent watery bowel movements are usually not a cause for concern.

If your concern is less about bowel movements and more about irritability or wakefulness, it may be helpful to consider other common reasons for these behaviors. In babies who are otherwise healthy and thriving, irritability and wakefulness are more often related to factors other than gastrointestinal discomfort.

(See infant colic for more information).

Your breastfed baby

It can be difficult to tell when a breastfed baby has diarrhea because healthy, thriving breastfed infants naturally have frequent, watery bowel movements that are not considered diarrhea.

Normal stools for an exclusively breastfed baby are soft or runny and often contain little white flecks that look like seeds. The color is generally yellow, mustard, or orange, but stools may occasionally have a greenish tinge. A breastfed baby may poop up to 10 times a day or may not poop for up to 10 days. Either extreme — or anything in between — can be perfectly normal when a baby is healthy and thriving.

You may suspect your breastfed baby has diarrhea if their bowel movements:

• are much more frequent than normal (for your baby)
• are frothy
• are “explosive” (shoot out with force)
• change color suddenly
• contain mucus or blood
• are unusually smelly

Other signs of illness in your baby, such as fever, vomiting (not to be confused with spitting up linked with gastro-esophageal reflux), poor feeding or nasal congestion, make the diagnosis of diarrhea more likely.

Your formula-fed baby

It is often easier to recognize diarrhea in a formula-fed baby because changes in bowel habits tend to be more noticeable. Formula-fed babies usually have firmer stools than breastfed babies; however, runny bowel movements can still be normal in many healthy, thriving formula-fed babies.

Normal stools for a formula-fed baby are generally soft and paste-like in consistency. Stool color can vary from grayish-green, yellow, tan, or brown, depending on the type of infant formula used. Bowel movements typically occur one to two times each day, or once every one to two days.

When your baby is eating solid food

Whether your baby is breastfed or formula-fed, the color, consistency, and frequency of bowel movements often change once solid foods are introduced. Stool color can vary widely depending on what has been eaten. Consistency usually thickens to a paste or formed stool and may contain undigested food; however, some foods can still result in looser bowel movements.

Changes in stool frequency and consistency, even from day to day, are common at this stage.

What causes diarrhea?

Babies and children can experience acute or chronic diarrhea. Babies (particularly breastfed babies) may also have frequent, loose, watery bowel movements that are completely normal and not a sign of illness.

Acute diarrhea is by far the most common form of diarrhea in babies and young children. Epidemiological studies suggest that young children in the United States experience, on average, around one to two episodes of diarrhea per year. Acute diarrhea is most often caused by:

• food poisoning
• an acute infectious illness
• an allergy or sensitivity to a food (or foods) eaten occasionally
• a reaction to medications used once or for a short period of time
• stress

In many cases, the exact cause of an acute episode of diarrhea is never identified. Because most diarrhea resolves on its own, determining the specific cause is often unnecessary.

Chronic diarrhea occurs far less often than acute diarrhea. In some cases, what is perceived as chronic diarrhea is actually the normal bowel pattern of a healthy infant. When chronic diarrhea does occur in babies and children, it is more commonly due to:

• unrecognized food sensitivities or allergies to foods eaten regularly (including milk)
• a chronic infectious illness
• a reaction to medications used regularly over a long period
• an underlying medical, digestive, metabolic, or functional disorder
• previous gastrointestinal surgery

1. Infectious illnesses

Symptoms of a gastro-intestinal infection (which includes food poisoning) are...

• fever;*
• nausea;
• vomiting;
• diarrhea;
• abdominal cramps;
• lack of appetite - refusing food (this may include fluids).

* Fever is a significant symptom of an infective illness and is not associated with any of the other reasons for diarrhea as discussed in points 2 to 6 below.

Food Poisoning

Food poisoning occurs after eating food or drinking water contaminated with germs such as bacteria or parasites. Unlike breast milk (which is naturally free of harmful germs), infant formula and solid foods can contain small amounts of bacteria.

When a baby or child is healthy, their immune system can usually cope with low levels of germs commonly found in food, including infant formula. However, if there is an overgrowth of these germs, which can occur with improper food storage, or if food becomes contaminated from another source, such as through poor hand hygiene, the body’s defenses may respond by trying to eliminate the germs.

This response often results in frequent watery bowel movements (diarrhea) and, in many cases, vomiting.

Gastrointestinal infection

Gastrointestinal infections (also known as gastroenteritis, stomach flu, tummy bug, or infectious diarrhea) can be caused by a wide range of viruses, bacteria, fungi, or parasites (such as protozoa, tapeworms, or roundworms) that enter a child’s body.

Viral infection
Viruses cause most acute episodes of diarrhea. Many different viruses can be responsible, including rotavirus, norovirus, cytomegalovirus, herpes simplex virus, and viral hepatitis. Viral gastrointestinal infections often involve vomiting for one or two days, with diarrhea lasting up to a week. These infections are usually not serious and typically require no specific treatment other than careful monitoring and prevention of dehydration, which can be a serious complication.

Bacterial infection
Less commonly, bacteria cause acute diarrhea. Salmonella, Campylobacter, Escherichia coli (E. coli), and Shigella are among the most common bacterial causes of diarrhea in Western countries. These infections can result in more severe illness and require prompt medical assessment for appropriate treatment. Babies and young children can become dehydrated quickly when bacterial gastrointestinal infection is present.

Parasitic infection
Occasionally, acute or chronic diarrhea may be caused by parasitic infection, most commonly Giardia lamblia. This parasite occurs more frequently in children attending childcare settings but can also be spread through contaminated drinking water. Other parasites that can cause diarrhea in children and adults include Entamoeba histolytica and Cryptosporidium.

2. Food or milk allergy or intolerance

Babies and young children have a higher incidence of food and milk allergies or intolerances than adults. This is largely due to the immaturity of their digestive and immune systems. Gastrointestinal symptoms may develop when nutrients such as carbohydrates, proteins, or fats found in milk or foods are poorly digested or tolerated.

Gastrointestinal symptoms can also occur as a result of sensitivity or allergic reactions to other substances present in foods, including naturally occurring compounds or added chemicals such as food additives, food enhancers, or salicylates.

Gastrointestinal symptoms of food or milk allergy or intolerance may include:

• vomiting
• excessive gas
• abdominal bloating
• abdominal cramps
• mucus or blood in stools
• diarrhea, with watery stools occurring hours after eating a particular food
• poor weight gain or weight loss in infants

Symptoms affecting the skin, nose, or lungs are more commonly associated with allergic reactions. (See milk allergy and intolerance for further information.)

Food intolerance or milk allergy

Diarrhea is a major symptom of an allergy or intolerance to proteins contained in milk or other foods. Where diarrhea is related to poorly digested proteins contained in infant formula (which is a formula fed infant's main source of nutrition) diarrhea will be chronic and weight will be affected (until more suitable milk is provided).

Variations in both the severity of diarrhea and subsequent affect on weight gained may be seen with respect to allergies or intolerances to other foods, due to the fact that these foods are often offered on a irregular basis and are not a major source of nutrition for babies and children. Or in the situation of an allergy or intolerance to proteins transferred in breast milk, symptoms are dependant on how often the food is consumed by a breastfeeding mother.

Lactose Intolerance

The inherited form of lactose intolerance is rare before the age of 4 years. In babies and young children, secondary lactose intolerance can be the reason for continued diarrhea following a bout of infectious diarrhea. Or lactose intolerance can occur as a result of inflammation of the intestines due to an untreated milk protein allergy or intolerance.

Lactose Overload

Lactose overload (also known as 'functional lactase deficiency') can be the reason for diarrhea in very young babies. Frequent watery bowel movements may develop due to an inability of many very young babies to digest all of the lactose contained in large volumes of milk. This is more common during in the early weeks of life but some babies can be affected for many months. Lactose overload is frequently misdiagnosed as lactose intolerance).

Carbohydrate Malabsorption

Carbohydrate malabsorption is also common in babies and young children due to immaturity of their digestive system. Young babies lack sufficient quantities of dietary enzymes necessary to break down the many different carbohydrates (which include sugars) contained in foods and fruit juice, hence diarrhea and other gastric symptoms can develop if these foods are offered too early (before 4 months) or in large quantities.

Children consuming large volumes of drinks with high sugar content e.g. fruit juice may also experience diarrhea due to carbohydrate malabsoption. Eating large quantities of 'sugar-free' sweets can also result in diarrhea in children and adults.

3. Medications

Many medications — including prescribed, over-the-counter, and herbal products — that are commonly given to babies and children can cause gastrointestinal side effects. In some cases, these effects may also occur when a breastfeeding mother is taking medication.

Examples include:

• Antibiotics (or exposure through breast milk when a nursing mother is taking antibiotics)
• Laxatives
• Antacid medications
• Prokinetic medications, used to alter gastric emptying in the management of gastro-esophageal reflux (some of which are now rarely prescribed due to safety concerns)
• Caffeine, found in cola drinks, tea, or coffee (which can be transferred through breast milk)
• Alcohol (ethanol), which may be present in some colic or wind preparations or transferred through breast milk

These medications may cause gastrointestinal side effects, including:

• reduced appetite
• nausea
• abdominal bloating due to excessive gas
• vomiting
• diarrhea (or, in some cases, constipation)

4. Stress

Emotional stress can contribute to diarrhea in babies and children. Stress affects the gut through the nervous system, altering gut motility and digestion. In response to stress, the bowel may move more quickly, reducing the time available for fluid absorption and resulting in looser stools.

In babies and young children, stress does not necessarily relate to emotional upset in the way adults experience it. Stressors may include illness, pain, fatigue, hunger, changes in routine, overstimulation, separation from a caregiver, or unfamiliar environments. Even positive changes, such as travel or starting childcare, can temporarily affect bowel habits.

Stress-related diarrhea is usually short-lived and tends to resolve once the underlying stressor is removed or the child adapts. When a child is otherwise healthy and thriving, stress alone is not a cause for concern but may help explain brief episodes of loose stools where no medical cause is identified.

5. Medical conditions, metabolic and functional disorders

The least common causes of chronic or recurrent diarrhea in babies and young children are underlying medical conditions, metabolic disorders, or functional disorders. Although there are many such conditions, they are rare.

When these conditions cause chronic diarrhea, they are typically associated with poor growth or weight loss. If a child is otherwise healthy and gaining weight appropriately, there is usually no reason for concern about these conditions.

However, if a baby or young child has ongoing diarrhea and is struggling to gain weight, a doctor may investigate further using appropriate diagnostic tests.

When to see a doctor

Seek medical advice if:

• your child has a fever
• vomiting lasts longer than 12 hours
• your child shows signs of dehydration
• stools contain blood or pus, or are black in color
• stools are foul-smelling or appear oily
• severe diarrhea lasts longer than 48 hours

For babies younger than three months, contact your doctor promptly if vomiting or diarrhea develops.

What tests might the doctor do?

Medical history and physical examination
Your child’s doctor will examine your child for signs of illness and ask about diet, feeding patterns, and recent changes. If you are breastfeeding, you may also be asked about your own diet and medication use.

Stool testing
You may be asked to collect a stool sample, which can be sent to a laboratory to check for bacteria, parasites, or other signs of infection.

Blood and urine tests
These tests may be used to rule out certain medical conditions or illnesses.

Dietary elimination
In some cases, elimination diets may be used to assess whether a food allergy or intolerance is contributing to diarrhea. This may involve changing infant formula or temporarily avoiding specific foods to see whether symptoms improve.

FAQ's

1. Is diarrhea a serious problem?

This very much depends on what is causing the diarrhea. Some children can become very unwell and may vomit, refuse fluids and become listless when they have diarrhea, while others may appear to be totally unaffected (except for the diarrhea).

Diarrhea can be dangerous for children under the age of 3 years, mostly due to the associated risk of dehydration, which in small children can occur in as little as 1 or 2 days if diarrhea is severe. While only a small number of children become dehydrated during an episode of infectious diarrhea, it's something all parents need to watch for.

2. How long will diarrhea last?

Diarrhea due to food poisoning often lasts for only 1 or 2 days. Rotavirus, which is the most common cause of infectious diarrhea, usually resolves in 3 to 9 days. Diarrhea lasting for longer than a week without any signs of improvement may require stool cultures or other diagnostic tests to determine the exact cause and the most appropriate treatment.

3. Is necessary to stop milk and dairy foods?

This really depends on whether your child is also vomiting or if she is dehydrated. While your child is vomiting your doctor may advise you to offer only clear fluids, such as oral rehydration solutions, for a short time before recommencing your child's regular diet.

If your baby is breastfed, breastfeeding should be continued as breast milk contains antibodies which will assist your baby's body to recover sooner. Offer more frequent breastfeeds while your baby has infectious diarrhea. You can also offer oral rehydration fluids between breastfeeds.

If your baby is formula fed, switching to a soy based infant formula while your baby has diarrhea may be helpful. A soy infant formula contains fiber (Isomil F) which can be effective at slowing down bowel movements. Don't dilute your baby's formula instead offer oral rehydration fluids between formula feeds. If diarrhea lasts for longer than a week your doctor may recommend using a soy infant formula or lactose-free formula for a few weeks before switching back to your baby's regular formula.

In past generations, parents were advised to automatically "avoid all dairy foods including milk" for at least 24 hours when a child has diarrhea, and then return milk at 1/2 strength for a period of time. More recent studies suggest that this practice is unnecessary and in some situations may be harmful because in most cases it does not shorten the length of the illness and it may deprive the child of much needed energy (calories/kilojoules) from milk and food. Where your child's appetite remains, restricting milk and dairy foods may result in your child becoming cranky due to hunger.

Yogurt can help to actively treat diarrhea from any cause. Yogurt contains probiotics such as Bifidus and Acidophalis which are friendly bacteria. Research has shown that probiotics can shorten the duration and severity of diarrhea. (Bifidus rather than Acidophalis, is recommended for babies younger than 12 months.)

4. What can my child eat?

Where your child has a good appetite, regular meals should be offered. A BRAT diet (bananas, rice, applesauce and dry toast) can be a good start. Carrots, rice cereal, potatoes may also help to slow down stools. Avoid other fruit or fruit juices until your baby's stools are back to normal, which should be within a week or so.

However, depending on how ill your child feels, she may not want to eat, so it's important not to pressure her. Fluids are much more important during an episode of infectious diarrhea. Where your child is not eating an oral rehydration solution should be offered. (See dehydration for more information).

5. Is there anything to avoid when a child has diarrhea?

• Never force your child to eat. A few days without food will cause her no harm, but a few days without fluids can. So focus your efforts on encouraging her to drink oral rehydration fluids.
• Do not give sugary drinks such as pop (soft drinks) Kool-Aid® (cordials) or fruit juice/drinks, Jell-O®, sweetened tea, broth or rice water. These have the wrong amounts of water, salts and sugar and could make your child's diarrhea worse.
• Do not give antidiarrheal medications to babies or children unless advised to do so by a doctor. Diarrhea is one way your child's body fights infection. Antidiarrheal medications may prevent her body from getting rid of the infection OR may conceal an underlying medical problem.

6. When is it safe to send my child back to day care?

This really depends on the cause of your child's diarrhea. Acute diarrhea is often highly infectious, meaning it can easily spread from one person to another. Day care facilities have strict guideline which exclude children from attending if they have infectious diarrhea. A doctor will be able to tell you when your child is well enough to return to day care.

7. How is diarrhea transmitted?

Germs are easily passed from one person to another (or sometimes from an animal to a person) by our hands or in food or drinking water. The most common way these germs are spread from people not washing their hands.

The germs are spread onto food, surfaces or other objects from persons with diarrhea (or who have changed the diaper of a child with diarrhea) who fail to adequately wash their hands. If others eat these foods or touch these surfaces and objects and fail to wash their own hands before they eat (or feed an infant), these germs can enter their body causing them to suffer and infectious diarrhea.

Because babies often suck their own hands; the hands of others; or just about any object they can get into their mouth, they are at greater risk of infectious diarrhea, particularly if they attend day care center.

8. Is it safe to continue to breastfeed when a mother has infectious diarrhea?

Yes! The organisms causing diarrhea are not transferred through breast milk. Breast milk has properties that will help to protect your baby from a gastro-intestinal infection, so continued breastfeeding is recommended. Because the organism can be transferred by hands, additional care needs to be taken with hand washing while any family member has infectious diarrhea, to avoid passing it to a baby or child.

Preventing diarrhea in babies and children

1. Take care with hygiene

• Wash your hands: before preparing formula; before feeding your baby; after changing your baby's diaper; before eating.
• Carefully clean formula bottles and sterilize them or allow to air dry if your baby is over 6 months old.
• Boil water used for making infant formula.
• Refrigerate prepared formula. (See Preparing and warming formula).
• Never reuse formula. Discard any unused formula within an hour of originally warming it for feeding.
• Transport formula carefully when you are out and about with your baby.
• Clean and boil or sterilize pacifiers regularly. Never put your baby's bottle or pacifier into your own mouth.
• Clean toys regularly with hot soapy water and dry in the sun.
• Clean surfaces with mild bleach at times of infectious diarrhea in any family member.
• Take care when cleaning your baby's diaper area to avoid spreading poop to the urethra area (the hole where urine comes out). Clean your baby's diaper area from front to back (especially important for baby girls).
• Do not retract your uncircumcised baby boy's foreskin. You do not need to clean under his foreskin until the end of puberty (which is sometime between to age of 12 and 18 years).

2. Avoid exposure to infectious illnesses

• Avoid taking a very young baby into crowded places such as shopping centers.
• Avoid knowingly exposing your baby to people with infectious illnesses.
• Where possible avoid the use of crowded child care centers before the age of 12 months.

3. Diarrhea due to medications

• Avoid the use of unnecessary medications.
• Avoid medications that contain ethanol (alcohol).
• Limit your caffeine intake if you are breastfeeding.
• Be aware of infant reactions to medications taken by a nursing mother.
• Discuss the possibility of side effects of individual medications with your doctor or pharmacist.

4. Diarrhea due to food or milk allergy or intolerance

• Breastfeed for as long as possible.
• Avoid starting solids too soon.
• Introduce only one new food at a time, spaced at intervals of 3 days apart, to observe for reactions.
• Do not give your baby fruit juice, except when treating constipation. (Fruit juice is not necessary for a balanced diet. Eating fruit and drinking water is a better alternative).
• See lactose overload for advice on feeding management.

DISCLAIMER: This information should not be used as a substitute for the medical care and advice of your child's doctor. There may be variations in treatment that your child's doctor may recommend based on individual facts and circumstances

By Rowena Bennett

About Rowena

Rowena Bennett (RN, RM, CHN, MHN, IBCLC) is a leading infant-feeding and sleep specialist and author of several books on infant feeding and behaviour, including the widely acclaimed “Your Baby’s Bottle-Feeding Aversion: Reasons & Solutions". With over three decades of clinical experience across child health, midwifery, mental health, and lactation, she has helped thousands of families worldwide understand and resolve complex feeding challenges through her evidence-based, baby-led approaches.

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