First, a doctor will try to determine if your symptoms are life-threatening or just debilitating. This is one of its markers when a doctor tries to differentiate between IBS and other illnesses. 

For doctors to accurately diagnose IBS, they generally must eliminate all other possible diseases. Pain and cramping can indicate conditions such as lactose intolerance, acid malabsorbtion or fructose malabsorbtion. Symptoms may be caused by a short term but dangerous illness. For instance, bacterial infections, parasitic infections and viruses can cause diarrahea. An intestinal blockage can seem like constipation. 

Blood in your stool indicates a possibly life-threatening condition. Rectal bleeding, much more than a drop, indicates a serious gastrointestinal problem such as Crohn's Disease or colitis. Bleeding should be a flag for you to go immediately to your doctor.

So, once a doctor eliminates viral, bacterial, cancerous or other organic cause, the doctor may then say that it is IBS. 

How Do You Get IBS? Can you catch it?

At this point, doctors do not believe that a person can 'catch' IBS. However, it is obvious that IBS either occurs or simply gets worse after serious gastrointestinal illnesses or stressful events.

For instance, some patients develop IBS as a post-infection illness. After a serious gastro intestinal event such as a bacterial infection, a flu or virus, some of the symptoms linger and they don't go away. If this is the case, a doctor may diagnose IBS and treat it accordingly.

Or, it may be a stressful life event that triggers the first symptoms of IBS. Workers in stressful jobs and students stressed out about college often report symptoms. Going through a divorce, the severe illness or death of a child, or the loss of job, home or business are examples of catastrophic life events that may trigger IBS. 

Sometimes IBS just comes on as we age. This may start in puberty, young adulthood, middle age or old age. Symptoms may be new or may simply get worse and become a daily fact of life. It is frustrating but true that IBS symptoms tend to get worse as we mature. 

IBS takes essentially three forms: diarrahea, constipation or a cycle of both. This also makes it difficult for a doctor to diagnosis it without running tests to be sure that there is not another underlying cause.

Although doctors aren't sure yet which comes first, IBS often accompanies such illnesses as chronic fatigue syndrome and fibromyalgia. It often accompanies clinical depression and anxiety. 

Diet is not the primary IBS factor, but it is one of the ways that IBS symptoms may be addressed. With no clear cause, doctors tend to focus on symptom relief.