Diarrhea: All You Need to Know, Doctor-Reviewed

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4 min read

Healthy Matters

The majority of the population has experienced diarrhea at one point or another. It may have been caused by having your favorite street food, touching your mouth with hands contaminated with germs, or as a reaction to certain medicines. It is very common in all people, particularly in children younger than five.


What is diarrhea?

Diarrhea occurs when you have 3 or more bowel movements in a day with abnormally soft, loose and watery stools. Nausea, vomiting, fever, abdominal pain and cramps, and bloating may accompany. Most cases can get better without treatment.


Types of diarrhea

  • Acute: lasting 1 or 2 days and clearing up without the need for medical care.
  • Persistent: lasting at least 2 weeks and less than 4 weeks.
  • Chronic: lasting 4 or more weeks.

Diarrhea is usually not serious, but it can be dangerous if complications occur, such as dehydration (thirst, dry mouth and dark-colored urine, etc.) and malabsorption (bloating, changes in appetite and weight loss, etc.). 


IMPORTANT: Infection-related diarrhea can spread via contaminated food and drinks, and sometimes air droplets of matters from vomiting. Stay at home from school or work until you have recovered and do not have diarrhea for at least 2 days.

What causes diarrhea?


Acute diarrhea and persistent diarrhea

Diarrhea, especially when acute and persistent, is mainly caused by intestinal infections.

  • Viruses: viral gastroenteritis is one common cause of acute diarrhea, especially in children. Other causative viruses include norovirus and rotavirus.
  • Bacteria: e.g. Campylobacter, E. coli and Salmonella. They cause diarrhea in a few hours after having contaminated food or fluids.
  • Parasites: e.g. Cryptosporidium enteritis and Giardia lamblia. Chronic diarrhea can appear if an infection does not go away in a short time or you have intestinal diseases, e.g. Inflammatory Bowel Disease and Celiac Disease. Electrolyte and hormonal imbalances can also cause diarrhea.
  • Food allergies: e.g. milk, eggs and seafood
  • Lactose intolerance
  • Fructose (sugar in fruits) intolerance or a diet rich in sugars
  • Artificial sweeteners: e.g. mannitol, which can be found in sugar-free sweets
  • Traveller’s diarrhea: diarrhea when traveling abroad, mostly due to contaminated food or drinks
  • Antibiotics: e.g. amoxicillin and cefuroxime. Antibiotics kill both good and bad bacteria, leading to rapid growth of another bacteria called C. Difficile that also causes diarrhea.
  • Antacids with magnesium: e.g. magnesium hydroxide
  • Chemotherapy: e.g. methotrexate and doxorubicin

When to see a doctor

See your doctor if you do not get better after OTC treatment or your symptoms worsen. You should also visit your doctor immediately if any of the following conditions happen:

  • Persistent diarrhea
    • Adults: more than 48 hours
    • Infants and children: more than 24 hours
  • Children under 12 months
  • High temperature (102°F or 39°C or higher)
  • Repetitive vomiting
  • 6 or more loose stools in 24 hours
  • Severe abdominal pain or rectal pain
  • Black stool
  • Blood or mucus in stool, bleeding from the buttocks
  • Symptoms of dehydration, e.g. feeling thirsty and decreased urination
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How to treat diarrhea


Replenish water and salt

It is important to replenish fluids and salts (e.g. sodium and potassium) while having diarrhea. Infants and children are at increased risk of dehydration. Oral rehydration salts (e.g. Oralite) are available over-the-counter in Hong Kong. Mix with the recommended amount of water, and sip little and slowly until diarrhea stops. You can also make it at home by mixing 6 level teaspoons of sugar, half level teaspoon of salt and 1L of clean drinking water together.


OTC antidiarrheals medications

Most diarrhea goes away without treatment. However, you can still use OTC antidiarrheals if needed, such as Charcoal tablets. Loperamide, bismuth subsalicylate (avoid if allergic to aspirin) and dioctahedral smectite generally are not advised unless absolutely necessary. OTC medications should not be given to infants and children aged below 12 as they can be dangerous. Always consult your doctor or pharmacist before taking them.



Your doctor may prescribe antibiotics if it is caused by bacteria, for example azithromycin and ciprofloxacin, and antiparasitics, such as mebendazole, to eradicate parasites.



Probiotics, for example lactobacillus, are good microorganisms that help increase the amount of good bacteria in your gut. They may be useful in managing antibiotic-induced diarrhea. Chronic diarrhea is treated according to the underlying diseases. If you have diarrhea from medications, talk to your doctor or pharmacist so they can help you adjust them. Viral diarrhea often goes away on its own. There are no particular antiviral drugs for treatment. 


If you would like to know where to buy medicines in Hong Kong, please check out this article:

What you can do to feel better

  • Avoid dairy products, spicy food, food or drinks high in fats, sugars or fibers or anything caffeinated.
  • Babies and young children can have their usual breast milk or formula diet.
  • Drink plenty of fluids and take small sips if needed.
  • Avoid vigorous exercise even if your diarrhea is mild.

How to prevent diarrhea

  • Oral vaccines are available for infants to prevent rotavirus infection (causes of viral gastroenteritis) in the private sector in Hong Kong. Contact your doctor for more information. First immunization should be done by the age of 8 weeks.
  • Ensure good personal hygiene, for instance proper handwashing with soap and water for about 20 seconds frequently.
  • Clean and disinfect anything, such as clothes and toys, with vomit on it separately with hot water.
  • Do not share towels, drinking glasses or eating utensils.
  • Pay attention to food and water hygiene, including when traveling, e.g. wash fruits and vegetables before eating, drink boiled water only, eat meat that is thoroughly cooked and served hot, and maintain refrigerators at a suitable and safe temperature for keeping food.
  • You may also take antibiotics prescribed by your doctor to prevent traveler’s diarrhea, for example levofloxacin and rifaximin. Other medications include bismuth subsalicylate and probiotics.


Dr. Lily Wong 黃淑婷醫生 is a family practitioner at The London Medical Clinic. She is both a registered general practitioner and a pharmacist in the UK and HK. Having lived and worked as a general practitioner for many years in busy practices in London, she relocated to Hong Kong with her family a few years ago. Dr. Wong has also been appointed Honorary Assistant Professor in the Department of Family Medicine at Hong Kong University, for her teaching of medical students.

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This article was independently written by Healthy Matters and is not sponsored. It is informative only and not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be relied upon for specific medical advice.

Dr. Wong Shu Ting Lily
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