What Causes Diarrhea

What Causes Diarrhea

What Causes Diarrhea

If your baby's stools suddenly become more frequent and more watery, she may have diarrhea. There are many causes of diarrhea. Find out how to tell if your baby has diarrhea, what may have caused it, and what you can do to ease her discomfort.

What is diarrhea?

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

Diarrhea can be acute which means it occurs suddenly and lasts for less than 4 weeks or chronic which means it lasts for longer than 4 weeks.

Diarrhea is not a condition; it is a symptom of a condition. There are numerous reasons why babies and children develop diarrhea, most are not serious and will either pass on their own or can easily be treated by a change in diet.  Because most episodes of diarrhea are short lived you may not always discover the cause.

How to tell when 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 child is ill.

Although changes in bowel habits can be related to a change in your baby's diet (or a nursing mother's diet), diarrhea doesn't automatically mean a food or milk allergy or intolerance is involved. Your child may experience brief episodes of diarrhea from time to time for no identifiable reason.

If your baby is healthy and is gaining good amounts of weight and also has lots of wet diapers (6 or more) each day, frequent watery bowel movements are not a cause for concern.

If your main concern is not so much related to your baby's bowel movements but due to irritability and wakefulness it may be wise to also consider the many other reasons for these behaviors to develop. More often than not, where a child is healthy and thriving, the reasons for irritability and wakefulness have nothing to do with gastric discomfort. (See infant colic for more information.)

Your breastfed baby

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

Normal stools for an exclusively breastfed baby are soft or runny and contain little while flecks that look like seeds. The color is generally yellow mustard or orange but occasionally may have a greenish tinge. Your breastfed baby may poop up to 10 times a day or may not poop for a up to 10 days and either extreme or anything between can be perfectly normal where your baby is healthy and thriving.

You may suspect your breastfed baby has diarrhea if her bowel movements...

  • are much more frequent than normal (for your baby);
  • are frothy;
  • are 'explosive' (i.e. shoot out with force);
  • change color;
  • contain mucus or blood;
  • are 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 much easier to tell when a formula fed baby develops diarrhea, because changes in bowel habits are more easily recognizable. Formula fed babies tend to have firmer stools compared to breastfed babies, and yet runny bowel movements can still be very normal in many healthy, thriving formula fed babies.

Normal stools for a formula fed baby are generally soft paste consistency, the color can vary from grayish green, yellow, tan or brown, depending on the type of infant formula used. The frequency of bowel movements for formula fed babies generally ranges from 1 or 2 times each day, to once every 1 or 2 days.

When your baby is eating solid food

Whether your baby is breastfed or formula fed, the color, consistency and frequency of her bowel movements can change once she starts eating solid foods. The color can vary greatly depending on what has been eaten. The consistency will generally thicken to a paste or formed stool and may contain undigested food; however some foods can cause runny bowel movements.  Changes in the frequency and consistency of stools, even on a day to day basis, are common.

What causes diarrhea?

Babies and children can experience acute or chronic diarrhea. Babies (particularly breastfed babies) can also have frequent loose watery bowel movements which are perfectly normal and not a sign that anything is wrong!

Acute diarrhea is by far the most common form of diarrhea in babies and children.  In the United States, children under 3 years old get sick with diarrhea 1.3 to 2.3 times a year on average.  Acute diarrhea is generally due to... 

  • food poisoning;
  • an acute infectious illness;
  • an allergy or sensitivity to a food (or foods) which is ingested occasionally;
  • a reaction to medications used once or for only a short time;
  • stress. 

Most of the time you won't find out exactly what's causing and acute episode of diarrhea, and since most diarrhea goes away by itself, the cause often doesn't matter.

Chronic diarrhea occurs far less often than acute diarrhea. (Often, what is perceived as chronic diarrhea, are the normal bowel movements of a healthy infant). In the rare incidences of chronic diarrhea in babies and children the reasons are generally due to...

  • unrecognized sensitivities or allergies to foods ingested regularly (this can include milk);
  • a chronic infective illness;
  • a reaction to medications used regularly over a long period;
  • a medical condition; digestive disorder; metabolic disorder; or functional disorder;
  • past gastro-intestinal 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 occurs from eating food or drinking water contaminated with germs such as bacteria and parasites. Unlike breast milk (which has no germs), infant formula and solid foods contain some germs. When your child is healthy, her body's immune system can handle low doses of germs which are commonly found in foods (including infant formula).

However, if there is an overgrowth of these germs (which can result from improper storage) or if food becomes contaminated by germs from another source (which occurs as a result of poor hand washing) her body's defenses will try to 'flush out' these germs by creating frequent watery bowel movements (diarrhea), and in many instances vomiting.


Gastro-intestinal infections (also known as gastroenteritis, stomach flu, tummy bug or infectious diarrhea) can be caused by any of many different viruses, bacteria, fungus or parasites (protozoa, tape worms or round worms) which can enter your child's body.

Viral infection:  Viruses cause most acute episodes of diarrhea. Many viruses cause diarrhea including Rotavirus, Norwalk virus, Cytomegalovirus, Herpes Simplex virus and viral hepatitis. A viral gastro-intestinal infection, in which vomiting may last for 1 or 2 days and diarrhea for up to a week, is not often serious and requires no treatment, except for prevention of what can be a serious complication, dehydration.

Bacteria infection: Occasionally bacteria causes acute diarrhea. Salmonella, Campylobacter, E.choli and Shigella are the most common types of bacterial infections causing diarrhea in western societies. These cause serious illness, which need an immedia medical assessment for proper treatment.  A child can quickly become severely dehydrated if they have a bacterial gastro-intestinal infection. 

Parasite infection: Occasionally acute or chronic diarrhea may be explained by an infection with the parasite Giardia Lamblia. Although occurring more commonly in children attending childcare centers, this parasite can also be spread in drinking water. Other parasites that cause diarrhea in children and adults include Entamoeba Histolytica and Cryptosporidium. 


Although occurring far less commonly than a gastro-intestinal infection, an untreated urinary tract infection (UTI) can be another reason for chronic diarrhea in babies and young children.

Signs of a UTI in babies and young children can vary greatly. The characteristic symptoms of a UTI commonly seen in adults are absent in babies and young children. Often the only indications of a UTI in babies and young children are non-specific symptoms such as...

* Fever is present in most babies and toddlers but often absent in babies younger than 1 month. Fever can also be absent in toddlers and children with recurrent or long-standing infections.

2. Food/milk allergy or intolerance

Babies and young children have an increased incidence of food/milk allergies and intolerances compared to adults, due to their immature digestive and immune systems. Gastric symptoms (described below) may develop as a result of poor digestion of nutrients such as carbohydrates, proteins or fats, found in milk or foods.

Gastric symptoms can also develop as a result of a sensitivity or allergic reaction to other chemical substances that are added to, or occur naturally in foods, e.g. food enhancers, food additives or salicylates. 

Gastric symptoms of food/milk allergies* or intolerance include...

  • vomiting;
  • excessive gas;
  • abdominal bloating;
  • abdominal cramps;
  • mucus or blood in stools;
  • diarrhea - watery stools occurring hours after eating a particular food;
  • failure to gain weight or weight loss in infants. 

* Other symptoms affecting the skin, nose and lungs are often linked with an allergic reaction.  (See milk allergy and intolerance for more on these.)


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. 


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 (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 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 (prescribed, over-the-counter and herbal) commonly given to babies and children such as...

  • Antibiotics - or where a nursing mother is taking antibiotics.
  • Laxatives.
  • Antacid medications
  • Prokinetics - medications used to speed up gastric emptying in the treatment of gastro-esophageal reflux disease e.g. cisapride (Propulsid®) and metroclopramide (Reglan®, Maxalon®)
  • Caffeine - contained in cola drinks, tea or coffee (caffeine can be transferred in breast milk)
  • Alcohol (ethanol) - contained in some colic/wind mixtures (or transferred in breast milk) 

...have side effects that include (among others)... 

  • Lack of appetite.
  • Nausea.
  • Abdominal bloating due to excessive gas.
  • Vomiting
  • Diarrhea (or constipation).

4. Stress

Emotional distress can cause diarrhea in children. 

5. Medical conditions, metabolic and functional disorders

The least common reason for chronic or recurrent diarrhea in babies and young children are the hundreds of rare medical conditions, metabolic and functional disorders, which involve the digestive tract as well as many conditions affecting other body systems. 

All conditions and disorders which are capable of causing chronic diarrhea will involve 'failure to thrive' or weight loss. Where your child is generally healthy and gains good amounts of weight there is no reason for you to be unnecessarily concerned about these conditions. However, where your child struggles to gain weight, your child's doctor may investigate the possibilities of these conditions through the use of diagnostic test.

When to see a doctor 

  • If your child has a fever.
  • If your child has been vomiting for more than 12 hours.
  • If your child show signs of dehydration.
  • If stools containing blood or pus, or are black in color.
  • If stools are foul smelling or appear 'oily-looking'.
  • If severe diarrhea lasts for longer than 48 hours.
  • In babies younger than 3 months call your doctor as soon as vomiting or diarrhea appears.

What tests might the doctor do?

Medical history and physical examination: Your child's doctor will examine your child for signs of illness. He/she will ask you about your child's diet and eating habits (or about your diet and use of medications if you are breastfeeding your baby). 

  • Stool culture: The doctor may provide you with a small container for you to collect a sample of your baby's poop to be sent to a laboratory for analysis, to check for bacteria, parasites or other signs of disease or infection.
  • Blood and urine tests may be used to rule out certain medical illnesses or conditions.
  • Elimination diets may be used to find out if a food allergy or intolerance is causing your child's diarrhea. The doctor may recommend changing your baby's formula or avoiding certain foods to see whether the diarrhea ceases in response to changes in diet.


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 Acidophaliswhich 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 

Written by Rowena Bennett

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