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The Many Causes of Diarrhea

The Many Causes of Diarrhea

Diarrhea is not a disease; it’s a by-product of some other condition that produces loose, watery stools with associated cramping and discomfort. The trick when diagnosing diarrhea is to find the underlying cause of this symptom, of which there can be many — everything from a mild “stomach flu” to irritable bowel syndrome (IBS) to cancer.

At Digestive Disease Consultants of Orange County, with locations throughout Orange County, California, our expert team of gastroenterologists understands that while everyone gets diarrhea from time to time, chronic diarrhea indicates an underlying medical condition that requires expert treatment. They’ve put together this guide to help you understand when diarrhea is just an annoyance and when you should seek out medical help.

Common causes of diarrhea

Many diseases, infections, and other conditions can cause diarrhea, including:


The Norwalk virus is often the cause of "stomach flu," also known as acute nonbacterial gastroenteritis. Illness from the infection begins 24-48 hours after exposure, and the symptoms persist from 12-48 hours. Other than resting and staying hydrated, there’s not much you can do; you have to let the infection run its course.

Rotavirus is a common cause of acute diarrhea in children, and the coronavirus that causes COVID-19 has also been linked with gastrointestinal symptoms, including nausea, vomiting, and diarrhea. Only testing can identify which virus is the cause.

Bacteria and parasites

Food or water that’s been contaminated with bacteria and/or parasites is the most common reason for food poisoning. And when traveling in developing countries where such contaminations are common, the diarrhea is often referred to as “traveler's diarrhea.”

Clostridium difficile is a hardy type of bacteria that causes serious infections and leads to explosive diarrhea. It most commonly occurs after a course of antibiotics or during a hospitalization where it’s easily spread.


A number of medications, such as most antibiotics, cause diarrhea as a side effect. You have a balance of naturally occurring bacteria in your digestive tract that aids digestion, but antibiotics destroy both good and bad bacteria, disturbing the normal balance and causing watery stool. Other medications known to cause diarrhea are chemotherapy drugs and antacids that contain magnesium.

Lactose intolerance

Lactose is a sugar found in dairy products. However, some people lack the enzyme that allows the body to digest it, resulting in diarrhea. Lactose intolerance tends to increase with age because enzyme levels drop after childhood.

Other digestive disorders

Inflammatory bowel disease, which includes Crohn's disease and ulcerative colitis, as well as celiac disease and irritable bowel syndrome, all affect the digestive tract, either causing damage to the tissues or preventing proper digestion. The end result? Diarrhea.

In addition, an overactive thyroid, diabetes, artificial sweeteners such as sorbitol and mannitol, or removal of the gallbladder can all lead to diarrhea.

If you see blood or mucus in your stool, experience weight loss, have a fever, or have become seriously dehydrated, you need to seek medical attention as soon as possible for treatment.

Diagnosing the reason for diarrhea

When you see a doctor, they may employ various methods to diagnose the root cause of your problem, including:

If none of those steps yields a definitive result, they might want to perform an endoscopy, to look at your upper GI tract; a sigmoidoscopy, to look at your lower colon; or a colonoscopy, to look higher up in your colon and take tissue samples.

Treating diarrhea

If the tests turn up nothing significant, chances are your diarrhea will clear up in a couple of days on its own; you just need to rest and remain well hydrated since you’re losing a lot of water in your stool.

If the diarrhea is caused by a bacterium or a parasite, the doctor may prescribe a course of antibiotics. In this case, treating the underlying infection is more important than any minor diarrhea caused by the medication. If you have a viral infection, antibiotics don’t work; you’re back to resting and staying hydrated. If you’re seriously dehydrated, the doctor may set you up with a saline IV to pump you full of fluids.

If it turns out you have a serious medical condition, like inflammatory bowel disease, the doctor will draw up a treatment plan specific to that condition.

If you’re experiencing diarrhea for more than 2-3 days, have a high fever, and/or are producing dark or bloody stools, come in to Digestive Disease Consultants of Orange County to see one of our gastroenterologists as soon as possible. Give us a call at any of our locations, or schedule your appointment online.

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