Digestive Health

The Complete List of What Causes Severe Diarrhea

By Kim Crawford, M.D. Last updated: September 6, 2018
what causes severe diarrhea


Acute, Sub-acute and Chronic Diarrhea

Are you spending too much time on the toilet? We sure don’t like to “talk poop,” do we? However, when there is something wrong, we sure know it. If you want to know the causes of diarrhea and what causes severe diarrhea, then we first need to clarify a couple of things.

What is severe diarrhea? Generally, it’s “severe” when people have more than 5 watery bowel movements per day. Really severe diarrhea can be secretory meaning water gushes into the colon; it can (literally) cause 50 trips to the bathroom day/night. Also, what some people call moderate, others call severe. I’ll reveal everything that can cause acute (happens all of a sudden), sub-acute (comes on gradually) and chronic (lasts more than 4-6 weeks) diarrhea.

What causes Severe Diarrhea that’s an Acute Illness?

Gastrointestinal viruses are probably the most common reason for acute (sudden onset) diarrheal illness. The Norwalk virus, cytomegalovirus, and even hepatitis all cause acute, often severe diarrheal illness. Bacteria can also cause acute problems. We can get “food poisoning” from salmonella, shigella and E. coli from our kids, and campylobacter (which is the only “zoonotic” bacterial diarrheal illness) from our dogs!

Zoonotic means animal to human transmission is possible. So, if your dog is treated for “campy,” he/she can give it to you too! Finally, in the “acute” category, let me add two unrelated things. Stress can cause acute diarrhea which is short lived as will the elusive C.difficile bacterial infection that follows a course of antibiotics. This can be dangerous; seek medical help immediately for post-antibiotic-treatment diarrhea.

If there is blood in the stools, really severe (“explosive”) symptoms or weight loss, seek medical care ASAP. The diagnosis might be ulcerative colitis or Crohn’s disease. (These are usually not categorized as “acute,” so they’ll be re-mentioned.)

The Causes of Diarrhea we call “sub-acute”

Parasites are rare if you haven’t been out of the country, but not unheard of especially if you have been swimming in lakes. Most parasitic diseases are not what people label as a cause of severe diarrhea. Usual symptoms include uncomfortable cramping, gas, bloating and some diarrhea. The most common causes of  “traveler’s diarrhea” are giardia and cryptosporidium.

Note: I’ll classify the remaining causes of diarrhea which people find to be severe as “chronic.” Chronic means it lasts more than 4-6 weeks and quite often will vary in intensity and severity. Let’s start out with common issues which you can easily discern.

What Causes Chronic (Often Severe) Diarrhea

 Lactose intolerance

what causes severe diarrhea As they teach us in medical school, common things are common. Lactose intolerance causes gas, bloating, cramping and diarrhea when you consume milk.

The solution for this is easy. Follow the anti inflammatory diet which strictly limits your dairy intake and, for your occasional raw yogurt or non-pasteurized cheese take the enzyme lactase. You can find good cashew milk and almond milk which do not contain gut-damaging carrageenan or guar gum to substitute for milk. Alternatively, you can follow a Paleo diet as well.

If this doesn’t fix the problem, there is more to it than lactose intolerance.

Controlling dairy if you have this problem will get rid of diarrhea, heal bloating without drugs (lactase is an enzyme; not a real drug), and will eradicate heartburn which is occasionally a feature of being lactose intolerant.

Beans Causing Gas and diarrhea

Some people don’t have enough enzymes to digest the fibrous part of certain beans. Try feeding your dog beans, and it will have the same effect. (I’m not kidding, but you’ll laugh!) However, for those with this problem, it’s not a laughing matter. If Beano (not a drug) doesn’t take care of the problem, then it’s not the beans. So, what else?

Celiac Disease and Gluten Intolerance

True celiac disease causes very severe symptoms for the wheat-eater who suffers from this disorder. Celiac disease is fairly easy to diagnose (see this blog) and a gluten free diet is mandatory for not just GI, but overall health.

There is ongoing research linking gluten in general to not only gastrointestinal upset but immune system depression, dementia and more.the causes of diarrhea

My feeling is we’ll keep finding more evidence about our inability to digest our current U.S.-made GMO gluten-containing products. In fact, I am convinced there will be more evidence forthcoming. My colleague, Dr. David Perlmutter is ahead of his time with his recommendation to do so. Here is his list of gluten free foods and recipes.

I now avoid all gluten and recommend you do the same. This may seem drastic, but it is my official recommendation.

Food Intolerances

Intolerance to a particular food or food group is different from a food allergy. Food allergies produce hives, rashes, throat swelling and what we recognize as allergic symptoms. Intolerance to food can cause any type of GI symptom, including severe diarrhea. Some people with non-celiac gluten sensitivity will have severe diarrhea when they eat gluten containing products.

Some people will have diarrhea when they eat lectin-containing foods such as kidney beans which are not adequately presoaked. I feel (and the bulk of the literature is starting to support this opinion) that everyone with multiple food intolerances has leaky gut (more on this to come).

Irritable Bowel Syndrome

Very often doctors will not have a solution or diagnosis for things like abdominal bloating, alternating constipation and diarrhea (what they call irritable bowel syndrome), chronic constipation, and so on. Of course, it can be IBS—the diarrheal-type which may involve bouts of severe diarrhea. There are pharmaceuticals which mask IBS. Actual treatment for IBS involves healing the leaky gut that is invariably a part of this syndrome.

Bile Acid Malabsorption

There are at least 25% of patients with IBS-diarrhea that end up being diagnosed as having bile acid malabsorption for a variety of reasons. Again, I wonder what percentage of these patients also have leaky gut?

Laxatives, Medications, and Sugars

If you are using too many laxative medications, you’ll give yourself diarrhea. Natural products such as 5-HTP (used to elevate serotonin levels) can cause diarrhea if the dosage is too high “for your system.” Medications (such as antacids) which contain magnesium can cause diarrhea. Finally, sugars such as sorbitol (chewing gum), mannitol and even fructose can cause diarrhea.

Inflammatory Bowel Disease

Both Crohn’s Colitis and Ulcerative Colitis can begin with watery, severe diarrhea. An editorial note here about these two disorders. Biologics are not necessarily necessary. Some cases of inflammatory bowel disease can be put into remission with the right combination of gut-fixing measures and a plethora of different probiotics. Don’t say yes to biologics unless you have explored this option.

SIBO and Candida

Small-intestinal bowel overgrowth means that the normally sterile end of the small bowel (the jejunum) receives a reflux of bacteria from the colon. This causes a host of symptoms including diarrhea. It usually occurs in the face of systemic illness, chemotherapy, repeated rounds of antibiotics and so on. The same conditions can produce candida (yeast) overgrowth in the colon; causing a range of symptoms including severe diarrhea.

Microcytic Colitis

Collagenous colitis and Lymphocytic colitis are sometimes associated with NSAID use. They can present with symptoms of severe diarrhea. Traditional treatment involves steroids. Recent literature shows a positive cure rate for lymphocytic colitis with Pepto-Bismol, of all things.

Leaky Gut

We can apply this diagnosis (in my opinion) to well over half the population. If you have been eating processed foods, GMO-foods, and grain-fed animal products, this is gut-disruptive. If you have taken or are taking NSAID’s, PPI antacids, antibiotics or many other pharmaceuticals, this is gut-disruptive.

Further, if you have had toxin exposure (mycotoxins or even dust mites); this is gut-disruptive. The symptoms are slow-to-evolve and include food intolerances initially (usually). As the GI lining gets more and more porous (hence the moniker leaky gut), the reactions become more systemic. Symptoms such as rashes, joint pains, and even cognitive difficulties have been attributed to this disorder.

Left untreated, it can progress to being the causative trigger for auto-immune disorders in the gut and elsewhere. This is treatable and curable. Read the articles linked above or search “leaky gut” in the search box below.


As you can see, the causes of diarrhea that may or may not “present” as severe are numerous. A proper diagnosis is, of course, necessary for accurate treatment. Don’t mask symptoms. Uncover the root cause and clean up your gut. A healthy gut means a healthy immune system and a healthy brain.

Even though it’s not a conversation-starter, it’s a popular topic. (“Diarrhea” is the fourth most googled “GI” condition!) I don’t expect anyone to share this on their Facebook page, but I sure do hope you share it with a loved one who needs help.


  1. Is it possible for leaky gut to “turn into” Crohn’s disease?

    • Gene-that’s a great question. Clinical studies have shown that leaky gut does indeed predispose us to auto-immune disease with Crohn’s being rightup there as a risk. This means if you have diarrhea or other symptoms being caused by what someone has diagnosed as leaky gut (please DO see a professional-hopefully someone in my field or a functional GI Specialist) you need the “right treatment.” Please see the blogs how to fix your gut and supplements for leaky gut. Sometimes you will not get the “full enchilada.” But again, DO see a Specialist and do NOT let symptoms just keep occurring or you can risk all sort of issues such as nutrient deficiencies, intestinal strictures and so on. Best of luck to you, Dr.Kim

  2. Really complete blog-I have a friend-true story-who will need to read it-thanks-she has gone Dr to Dr and I now think she has leaky gut.

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