Chronic Fatigue Syndrome

Myalgic Encephalomyelitis (ME) · Chronic Fatigue Immune Dysfunction Syndrome (CFIDS)

The Facts

Chronic fatigue syndrome (CFS) is a condition causing persistent fatigue that lasts for at least 6 months (or longer) and isn't due to another medical condition (e.g., hypothyroidism) plus four or more specifically defined associated symptoms. It was once thought to affect only highly educated young adults who are "high achievers" or career-oriented professionals. It is now known that CFS affects people of all ages and from all walks of life.

CFS is about 2 times more common in women than in men. It is associated with extreme and prolonged fatigue that isn't relieved by rest. People with CFS experience persistent tiredness so severe that it may prevent them from working, exercising, and enjoying life. CFS is a poorly understood condition and there is no clear consensus about its diagnosis and treatment.

CFS is also known as myalgic encephalomyelitis (ME) or chronic fatigue immune dysfunction syndrome (CFIDS).


The exact causes of CFS are unknown, but it appears to be triggered by many different factors. Viral infections, genetic predisposition, and immune reactions are all considered possible causes of the disorder. The persistent tiredness was once attributed to a virus called the Epstein-Barr virus (this virus is responsible for mononucleosis) but the link remains scientifically unproven and is no longer considered a potential cause.

Several other potential causes of CFS are being studied including issues with sleep disruption, endocrine-metabolic dysfunction, and neurally mediated hypotension. Two-thirds or more of patients with CFS meet existing psychiatric criteria for anxiety disorders, dysthymia, or depression, but whether it is the cause or the result of CFS remains unclear. There is some evidence suggesting that CFS is an immune disorder, causing the body's defense system to function abnormally particularly in response to stress. This does not mean that the immune system is weakened, however.

It's likely that not one single factor is responsible, but rather a combination of factors. Physical activity and physical or emotional stress seems to make CFS worse. But, further research is needed to figure out its causes and to better understand this puzzling condition.

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The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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