Conditions InDepth: Chronic Fatigue Syndrome (CFS)

Chronic fatigue syndrome (CFS) is a long term, disabling, and complex disease. It causes extreme fatigue that makes it hard for those who have it to get through the day. It often causes problems for people who work and go to school. Rest does not make the any of the problems better.

CFS is also known as systemic exertion intolerance disease (SEID). It’s very hard to diagnose. Test results appear normal even when symptoms are present. Other causes need to be ruled out. As such, many people may have CFS without a diagnosis. In others, it may be a long time before one is made.

People with CFS often have problems for many months to years. Their problems range in severity. Some people get better over time, while others get worse. But, most people settle into a cycle of remission and flare ups.

No one knows what causes CFS. For more than a century, doctors have reported seeing illnesses that were just like it. In the 1860s, Dr. George Beard named it "neurasthenia." He thought it was a nervous disorder with weakness and fatigue. The most common theory today is that CFS is set off by an infection or other immune system.



Chronic fatigue syndrome. EBSCO DynaMed Plus website. Available at: http://www.dynamed.... Updated August 30, 2018. Accessed June 7, 2018.
Chronic fatigue syndrome. Merck Manual Professional Version website. Available at: Updated October 2016. Accessed June 7, 2018.
Treatment. Centers for Disease Control and Prevention website. Available at: Updated July 3, 2017. Accessed June 7, 2018.
Yancey JR. Thomas SM. Chronic fatigue syndrome: diagnosis and treatment. Am Fam Physician. 2012;8(68):741-746.
Last reviewed May 2017 by EBSCO Medical Review Board James P. Cornell, MD
Last Updated: 6/7/2018


EBSCO Information Services is fully accredited by URAC. URAC is an independent, nonprofit health care accrediting organization dedicated to promoting health care quality through accreditation, certification and commendation.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

To send comments or feedback to our Editorial Team regarding the content please email us at Our Health Library Support team will respond to your email request within 2 business days.