• Also Known As:
  • CFS
  • Chronic Fatigue and Immune Dysfunction Syndrome
  • Myalgic Encephalomyelitis
  • ME
  • Systemic Exertion Intolerance Disease
  • SEID
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What is chronic fatigue syndrome?

Chronic fatigue syndrome (CFS) is a disorder that causes ongoing, extreme fatigue that is not explained by any known medical condition. It can affect a person’s ability to perform routine, daily activities or tasks.

People with CFS sleep poorly and awake unrefreshed. They have frequent headaches, muscle and joint pain, recurring sore throats, and memory and concentration problems. The intensity and type of symptoms can vary from day to day and from person to person, but typically the extreme fatigue lasts at least 6 months or more. On a “good day,” symptoms may be mild and someone with CFS may be able to function at a near normal level; on a “bad day,” they may be unable to get out of bed. Their condition is not improved by bed rest and can be worsened by mental activity.

CFS exists worldwide in every age, income bracket, and ethnic group, and in both sexes. CFS is about three to four times more common in women than in men and it appears to be most prevalent in the 40- to 50-year age range. The Centers for Disease Control and Prevention (CDC) estimates that at least one million people in the U.S have CFS but that less than 20% of those affected have been diagnosed or know that they have the condition.

It is not known what causes CFS. While a single cause may yet be identified, many researchers believe that CFS has multiple triggers. These may include:

  • Viral infection such as Epstein Barr virus, although no microbe has been proven to be the cause
  • Immune dysfunction provoked by trauma, stress, or allergy, which in turn triggers CFS
  • Nutritional deficiency
  • Abnormally low blood pressure (neurally mediated hypotension) that can cause fainting
  • Disturbance of the hypothalamic-pituitary-adrenal (HPA) axis, possibly caused by inactivity, sleep disturbance, psychiatric comorbidity, medication, or ongoing stress

Researchers have observed family patterns and believe there may be a tendency to an inherited predisposition of the condition. Some investigators feel that further research will reveal that CFS is not a single condition at all but a group of different disorders with a similar end point.

It is known that those affected by CFS have a definite onset of symptoms, that is, a time before which they felt well and had the energy for normal daily tasks. About 75% of the time, CFS is preceded by what appears to be a flu-like illness. Other cases of CFS arise following a period of intense physical or emotional stress, and some emerge slowly with those affected noticing a gradual decline in their energy and sense of well-being.

A large number of other diseases, disorders, and temporary conditions can cause or display similar symptoms or side effects. Examples include hypothyroidism, mononucleosis, psychological disorders, eating disorders, cancer, autoimmune disease, infections, drug or alcohol abuse, reactions to prescription medications, and – for whatever reason – not getting enough hours of uninterrupted sleep. In these cases, an underlying reason for the fatigue can be established and often treated. This temporary, short-term, or long-term fatigue must be distinguished from CFS.

To date, there is no single test or evaluation that can diagnose CFS. However, there is a set of signs and symptoms used as criteria to help identify it.


About Chronic Fatigue Syndrome (CFS)

Signs and Symptoms

The Centers for Disease Control and Prevention (CDC), in conjunction with an international panel of CFS research experts, adopted a definition of chronic fatigue syndrome that requires the following signs and symptoms:

  • Severe chronic fatigue lasting 6 consecutive months or longer with other known medical conditions excluded by clinical diagnosis
  • Daily activities and work severely affected
  • Four or more of the following 8 symptoms occurring at the same time and lasting or recurring for more than 6 months:
    • Inability to concentrate; problems with short-term memory or attention span
    • Sore throat that is frequent or persistent
    • Tender lymph nodes in the neck or armpit
    • Muscle pain
    • Pain in multiple joints but without swelling or redness
    • Headaches that are a new type, more severe, or occur in a new pattern
    • Waking up unrefreshed
    • Extreme fatigue lasting more than 24 hours after physical or mental exercise

In 2015, the National Academy of Medicine (formerly the Institute of Medicine (IOM)) Committee on Diagnostic Criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome released a report that proposed new diagnostic criteria for CFS intended to improve diagnosis and care of those affected by CFS. Some of the criteria are the same as those listed above and a healthcare practitioner may apply some of them when evaluating a patient. To be diagnosed with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a person must have the following three symptoms:

  • Extreme fatigue for more than 6 months with a decreased ability to function in everyday activities, such as work, school, social events or personal care; the fatigue and dysfunction must be new or have a definite beginning, not be caused by continued excessive exercise, and not greatly improved by resting.
  • Feeling “out of sorts” (malaise) or having a general feeling of discomfort after exercising or expending energy
  • Waking up unrefreshed

At least one of the following two symptoms must also be present and will be evaluated for how often and how severe they occur. They should affect the person at least half the time and be at least moderately intense.

  • Inability to concentrate; problems with memory or attention span (cognitive impairment)
  • Feeling light-headed or dizzy, fainting, or having heart palpitations after standing upright from a seated or resting position (orthostatic intolerance)

**Adapted from Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness

Besides the primary symptoms of CFS, a variety of other symptoms may be commonly seen. These include:

  • Abdominal pain, bloating, nausea, vomiting, loss of appetite
  • Allergies and sensitivities to foods, odors, chemicals, medication, and sound
  • Chest pain
  • Chills and night sweats
  • Chronic cough
  • Depression and anxiety
  • Frequent urination
  • Heat and cold sensitivity
  • Low body temperature
  • Dry eyes or mouth
  • Earaches
  • Jaw pain
  • Low-grade fever
  • Joint stiffness, particularly in the morning
  • Numbness, tingling, or burning sensation in the face hands or feet
  • Shortness of breath


At this time, there is no blood test, imaging scan, or other test to diagnose chronic fatigue syndrome. The syndrome is diagnosed by excluding other possible causes. This typically involves:

  • Documenting the patient’s medical history
  • Performing a thorough medical examination
  • Conducting cognitive function tests
  • Ruling out other conditions that may be causing or worsening the fatigue (and/or identifying and treating those that can be treated)
  • Fulfilling the Centers for Disease Control and Prevention (CDC) or the National Academy of Medicine criteria for the definition of CFS
  • Monitoring the patient over time to see if other underlying conditions arise

Patients may get a classification of unknown or idiopathic chronic fatigue if they do not meet the CDC’s or National Academy of Medicine’s symptom criteria for CFS or do not exhibit severe enough fatigue.

Laboratory tests can be useful to help diagnose and manage other conditions with similar symptoms and disorders that must be identified and treated before a diagnosis of CFS can be made. The CDC provides a set of basic tests that may be done, but these may vary depending on the healthcare provider:

Laboratory tests

Additional tests may be ordered to follow up abnormal findings on the general tests and as warranted by signs and symptoms. These additional tests are used to help identify or rule out diseases and disorders that may cause signs and symptoms similar to CFS, such as fatigue. A few examples include:

Non-laboratory tests
Occasionally, an MRI (magnetic resonance imaging) scan may be ordered to help rule out multiple sclerosis as a cause of chronic fatigue. Other tests and imaging scans may be used in a research setting but are not considered clinically useful at this time.


As there is currently no cure and there are no specific drugs developed for chronic fatigue syndrome, treatment focuses on symptom relief and lifestyle changes. These include:

  • Cognitive behavioral therapy (CBT)
  • Sleep management techniques
  • Relaxation and stress-reduction techniques, including yoga, meditation, massage therapy and deep breathing exercises
  • Medication to reduce pain discomfort, and fever
  • Medication to treat anxiety (anti-anxiety drugs)
  • Medications to treat depression (anti-depressant drugs)

Some medications can cause reactions or side effects that may be worse than the symptoms of CFS.

Many people with CFS will get better over time, but some degree of illness may persist for years or for a lifetime. Medical experts recommend that those with CFS track their energy levels and budget their time and activities. Eating well and getting regular amounts of moderate (but not excessive) exercise can help maintain functional abilities and improve a person’s mood and ability to sleep. Support groups and counseling can help a person deal with the physical, psychological, financial, and social frustrations caused by CFS.

People with CFS should work with their healthcare providers to determine the best course of treatment for them. What works for one person may not work for another, and many with CFS are especially sensitive to medication side effects.

View Sources

Sources Used in Current Review

Centers for Disease Control and Prevention (CDC). Chronic Fatigue Syndrome Awareness Day. Available online at http://www.cdc.gov/Features/cfsawarenessday/. Accessed October 2016.

CDC. Chronic Fatigue Syndrome. Available online at http://www.cdc.gov/cfs/general/index.html. Accessed October 2016.

CDC. Chronic Fatigue Syndrome. The 1994 Case Definition. Available online at http://www.cdc.gov/cfs/case-definition/1994.html. Accessed October 2016.

CDC. Chronic Fatigue Syndrome. Diagnosis. Available online at http://www.cdc.gov/cfs/diagnosis/. Accessed October 2016.

CDC. Chronic Fatigue Syndrome. Patient Examination Process for CFS. Available online at http://www.cdc.gov/cfs/diagnosis/step-6.html. Accessed October 2016.

Feb. 16, 2016. CDC Public Health Grand Rounds: Chronic Fatigue Syndrome: Advancing Research and Clinical Education. Available online at https://www.cdc.gov/cdcgrandrounds/pdf/archives/2016/feb2016.pdf. Accessed October 2016.

Nov. 13, 2015. Healthline. CFS (Chronic Fatigue Syndrome). Available online at http://www.healthline.com/health/chronic-fatigue-syndrome#Overview1. Accessed October 2016.

December 2015. The Lancet Psychiatry. Rehabilitative treatments for chronic fatigue syndrome: long-term follow-up from the PACE trial. Available online at  http://thelancet.com/journals/lanpsy/article/PIIS2215-0366(15)00317-X/fulltext. Accessed October 2016.

(February 10, 2015) National Academy of Medicine. Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. Available online at http://www.nationalacademies.org/hmd/Reports/2015/ME-CFS.aspx. Accessed November 2016.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Klein, J., Reviewed (2002 June, Reviewed). KidsHealth for Parents, The Nemours Foundation [On-line information]. Available online at http://kidshealth.org/parent/system/ill/cfs.html.

Hanna, E. (2002 September, Reviewed). Chronic Fatigue Syndrome. What is Chronic Fatigue Syndrome (CFS)? 4woman.gov, The National Women’s Health Information Center [On-line information]. Available online at http://www.4woman.gov/faq/cfs.htm.

About CFID. CFIDS (Chronic fatigue and immune dysfunction syndrome) Association of America [On-line information]. Available online at http://www.cfids.org/about-cfids/symptoms.asp.

(2003, September 18, Reviewed). Chronic Fatigue Syndrome. CDC, National Center for Infectious Diseases [On-line information]. Available online at http://www.cdc.gov/ncidod/diseases/cfs/info.htm.

(2003 September 18, Reviewed). The Revised Case Definition (abridged version). CDC, National Center for Infectious Diseases [On-line information]. Available online at http://www.cdc.gov/ncidod/diseases/cfs/defined/defined2.htm.

(2003 February, Updated). Chronic Fatigue Syndrome. Familydoctor.org [On-line information]. Available online at http://familydoctor.org/x1598.xml.

Craig, T., and Kakumanu, S. (2002 March 15). Chronic Fatigue Syndrome: Evaluation and Treatment. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20020315/1083.html.

(2001 January). Chronic Fatigue Syndrome. NIAID [On-line information]. Available online at http://www.niaid.nih.gov/factsheets/cfs.htm.

(2003 September 23). Aetna Clinical Policy Bulletins [On-line information]. Available online at http://www.aetna.com/cpb/data/PrtCPBA0369.html.

Chronic fatigue syndrome. AccessMed Health Information Library [On-line information]. Available online at http://www.ehendrick.org/healthy/.

Carter Batiste, L. and Loy, B. (2003 November 05). Accommodating People With Chronic Fatigue Syndrome. Job Accommodation Network [On-line information]. Available online at http://www.jan.wvu.edu/media/cfs.html.

Mayo Clinic staff (2003 October 02). Chronic fatigue syndrome. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/invoke.cfm?id=DS00395.

Kova, B. (2002 April 25). MedlinePlus Health Information Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001244.htm.

(2003 October 14, Updated). Chronic Fatigue Syndrome Bytes. National Jewish Medical and Research Center [On-line information]. Available online at http://nationaljewish.org/cfsbytes.html.

Chronic Fatigue Syndrome. Merck Manual – Second Home Edition [On-line information]. Available online at http://www.merck.com/mrkshared/mmanual_home2/sec25/ch306/ch306b.jsp.

McLaughlin, Jill. Understanding Chronic Fatigue Syndrome. Co-Cure [On-line information]. Available online at http://www.co-cure.org/Understanding%20Chronic%20Fatigue%20Syndrome.htm.

Davis, C. What’s in a Name: Fibro vs. CFS. Arthritis Foundation [On-line information]. Available online at http://www.arthritis.org/resources/news/news_fibro_cfs.asp.

(2006 May 9). Chronic Fatigue Syndrome, For Patients, Caregivers, Consumers. CDC [On-line information]. Available online at http://www.cdc.gov/cfs/consumers.htm. Accessed on 4/20/08.

(2007 June 22). Chronic Fatigue Syndrome. MayoClinic [On-line information]. Available online at http://www.mayoclinic.com/health/chronic-fatigue-syndrome/DS00395/DSECTION=3. Accessed on 4/20/08.

Christopher-Stine, L. (2006 August 22, Updated). Chronic Fatigue Syndrome. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001244.htm. Accessed on 4/20/08.

(2006 July 11, Modified). CFS Toolkit for Health Care Professionals: Basic CFS Overview. CDC Chronic Fatigue Syndrome [On-line information]. PDF available for download at http://www.cdc.gov/cfs/pdf/Basic_Overview.pdf. Accessed on 4/26/08.

(Updated June 4, 2007) Centers for Disease Control and Prevention. Chronic Fatigue Syndrome, Possible Causes. Available online at http://www.cdc.gov/cfs/cfscauses.htm. Accessed October 2008.

(2011 June 18) Mayo Clinic Staff. CFS, Risk Factors (Online Information). Available online at http://www.mayoclinic.com/health/chronic-fatigue-syndrome/DS00395/DSection. Accessed September 2012.

(2011 September 15) Davis, C.P., Balentine, J.R. Chronic Fatigue Syndrome. Medicine Net.com (Online information). Available online at http://www.medicinenet.com/chronic_fatigue_syndrome/article.htm. Accessed September 2012.

Shiel, W.C Jr., Stoppler, M.C. Chronic Fatigue Syndrome. Emedicinehealth.com (Online information). Available online at http://www.emedicinehealth.com/chronic_fatigue_syndrome/article_em.htm. Accessed September 2012.

(2012 May 16) Centers for Disease Control and Prevention. Chronic Fatigue Syndrome. CDC.gov/cfs (Online information). Available online at http:// www.cdc.gov/cfs/general/. Accessed September 2012.

(2012 February 2) Chronic Fatigue Syndrome, pubmed.com (Online information). Available online at http://Ncbi.nlm.nih.gov/pubmedhealth/PMH0002224. Accessed September 2012.

(October 2011) Carruthers B, et al. Myalgic encephalomyelitis: International Consensus Criteria. Journal of Internal Medicine Volume 270, Issue 4, pages 327–338. Available online at http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2796.2011.02428.x/abstract. Accessed June 2012.