Crohn's disease is one of the two most common forms of inflammatory bowel disease (IBD). The other is ulcerative colitis. IBD is often confused with the condition known as irritable bowel syndrome (IBS). 

Although the two disorders share similar-sounding names and some of the same symptoms, they’re distinct from one another. Unlike Crohn's disease, which has around 700,000 sufferers in the United States, IBS is extremely common. 

According to the International Foundation for Functional Gastrointestinal Disorders, between 10 and 20 percent of U.S. adults struggle with IBS. Next to the common cold, IBS is the second leading cause of employee absenteeism. 

Most people with IBS will never develop IBD, but a person who has been diagnosed with IBD may display IBS-like symptoms.

What is IBS?

Like IBD, IBS is a chronic condition.  

But unlike IBD, IBS isn’t classified as a true disease, but instead is known as a "functional disorder." A functional disorder is a condition for which there are is a collection of symptoms that lack an identifiable cause. Other examples of functional disorders include tension headaches and chronic fatigue syndrome. People with IBS are also more likely to experience other functional disorders, such as chronic fatigue syndrome, the above-mentioned CFS, fibromyalgia, and temporomandibular joint disorder.

However, contrary to popular belief, IBS is not isn’t a psychological condition. IBS has physical symptoms—it's just that those symptoms can't be traced to a physiological cause. It's sometimes called mucous colitis or spastic colitis but those names are technically incorrect, as colitis is an inflammation of the colon, whereas IBS does not cause inflammation. 

As mentioned, people with IBS show no signs of a disease and tests usually come back normal. Although it’s sometimes called “mucous colitis” or “spastic colitis,” those names are technically incorrect, as colitis is an inflammation of the colon, whereas IBS doesn’t cause inflammation.

Symptoms of IBS

IBS is characterized by abdominal pain or cramps, diarrhea, constipation, or by a combination of those symptoms.

Like for those with IBD, IBS sufferers will often experience urgent bowel movements. But they will most often display atypical symptoms as well. Inconsistent symptoms include irregular bowel habits, such as alternating diarrhea and constipation, as well as misplaced abdominal pain. 

IBS patients may experience a feeling of incomplete evacuation as well. Pain may be experienced across the entire abdomen, but it most often manifests in either the lower right or lower left side. A minority of those with IBS will experience upper right-side abdominal pain without any other symptoms. 

IBS also differs from IBD in the amount of stool produced. A person with IBS may indeed have loose stool, but stool volume will actually fall within the normal volume limits over a 24-hour period. (Diarrhea is defined by volume— not, as many believe, by consistency.)  

IBS sufferers with constipation typically have normal colonic transit times—(the amount of time it takes for stool to travel from the colon to the rectum)—as well. 

Depending upon the main symptom, IBS patients are classified as constipation-predominant, diarrhea-predominant, or pain-predominant. 

IBS, IBD, and Stress

Because objective abnormalities that occur with IBD patients (such as deep ulcerations or narrowing of the intestines) are absent in IBS patients, it’s difficult for researchers to understand the precise causes of the latter condition.  

One notable difference between the two disorders, however, is that IBS is almost always exacerbated by stress, whereas IBD may flare-up equally in either low-stress andor high-stress situations. 

According to Fred Saibil, M.D., author of the book Crohn's Disease and Ulcerative Colitis, because of social stigmas many people don't feel they can discuss IBS as they would a tension headache, for instance, because of social stigmas. 

"You don't hear a lot of people talking about their 'tension vomiting' or 'tension diarrhea' or 'tension bellyaches,'" he says, "even though these are every bit as common." 

Dr. Saibil notes also that there’s still some confusion over IBD because doctors once believed that IBD the condition was caused by stress. There’s no evidence that that is the case, however, and IBD patients should in no way feel they brought the condition on themselves.

Treatments for IBS

Although IBS sufferers may find relief with certain medications, including intestinal antispasmodics such as Levsin (hyoscyamine) or a dicyclomine dicyclo-mine HCL like (Bentyl), the preferential treatments, by far, are lifestyle and dietary modification. 

Whereas IBD patients must rely mostly on pharmacological therapies to control their symptoms, many IBS patients find relief by attempting to minimize and control their stress as much as possible. Stress reduction techniques such as mediation, yoga, and talk therapy have proven helpful for many. 

People with IBS should avoid "aggravating" their condition with fried and fatty foods and caffeinated beverages as well.