What causes chronic fatigue syndrome (CFS)?

The causes of chronic fatigue syndrome tend to be unexplained because the factors associated with symptoms of CFS are often too numerous to account for. However, researchers have been investigating the possibility of possible physical causes of CFS, including: low levels of sugar in the blood (hypoglycemia), anemia, allergies, hormonal disorders, deficiencies in diet, or immune system diseases. Research has also been done to determine how chronic fatigue syndrome relates to viral diseases such as human herpesvirus, human immunodeficiency virus (HIV), or Epstein-Barr virus, though the results have been inconclusive. Although 65 percent of Americans diagnosed with chronic fatigue syndrome have also experienced a history of allergies, the relation between the two remains unclear. Some research suggests more psychological causes of chronic fatigue syndrome such as depression or mental stress. However, CFS can also be a reaction to certain medications or chronic conditions such as recovery from surgery.

No one knows for sure what causes CFS. Many people with CFS say it started after an infection, such as a cold or stomach bug. It also can follow infection with the Epstein-Barr virus. This is the same virus that causes infectious mononucleosis (sometimes called "mono"). Some people with CFS say it started after a time of great stress, such as the loss of a loved one or major surgery.

It can be hard to figure out if a person has CFS because extreme tiredness is a common symptom of many illnesses. Also, some medical treatments, such as chemotherapy, can cause extreme tiredness.

This answer is based on source information from National Women's Health Information Center.

William B. Salt II., MD
Chronic fatigue syndrome is one of many interrelated functional symptom syndromes, composed of medically unexplained symptoms, which are “caused” by dysfunction involving the mind/brain—body connection.

To explain the unexplainable and cause, look at the terms used here and then “see the big picture.”


Functional refers to how the body works.

Symptoms of chronic fatigue syndrome: extreme fatigue that may worsen with physical or mental activity and not improve with rest

Symptom Syndromes are collections of medically unexplained symptoms. They are also known as functional somatic syndromes and chronic multisymptom illnesses. Nearly every specialty defines at least one syndrome. Examples include RHEUMATOLOGY (fibromyalgia), UROLOGY (interstitial cystitis/painful bladder and chronic prostatitis/painful prostate), and GASTROENTEROLOGY (irritable bowel syndrome).

Medically Unexplained Symptoms (MUS) cannot be explained by medical tests, because they are caused by dysfunction.

Dysfunction is disturbance or “malfunction” of how the body works.

Mind/Brain-Body Connection refers to how the mind/brain and body communicate and talk with one another.

MUS and symptom syndromes frequently overlap with one another and are commonly associated with and often attributed to stress, depression, anxiety, and/or panic. Medical and scientific research is showing how the mind/brain and body communicate and both how and why symptoms are generated. One of the most important discoveries is that the "central" mind/brain can become "sensitized" to "peripheral" body pain and symptom signals. So these symptom syndromes are now being called, central sensitivity syndromes.

This author and Thomas L Hudson, MDiv JD (, propose a new unifying and holistic medical model of medically unexplained symptoms and their related symptom syndromes as chronic disease, explain both how and why they occur, and show what people can do to help themselves and work effectively with their caregivers.

DISEASE IS DYSFUNCTION, AND SYMPTOMS ARE THE EXPRESSION. The cause of medically unexplained symptoms and pain can be understood as disease/dysfunction, regardless of whether the symptoms are widespread (e.g., the fatigue of chronic fatigue or the pain and fatigue of fibromyalgia) or localized to a specific area of the body (e.g., the abdominal pain and bowel dysfunction of irritable bowel syndrome). 

Mosaraf Ali, MD
Integrative Medicine

Chronic Fatigue Syndrome (CFS) affects about 80 percent of the urban population. A syndrome is not a disease but a combination of symptoms that are most likely to manifest themselves in a group. These symptoms may not have a single cause, like a disease has. There are numerous syndromes like irritable bowel syndrome, premenstrual syndrome, Down's syndrome, etc.

CFS is characterized by the following symptoms: chronic persistent fatigue, muzzy head, headaches, dizziness, muscle aches, insomnia, and lack of concentration. Sometimes CFS is caused by viral infection (Glandular Fever) when extreme fatigue and muscle aches are predominant symptoms. Neck stiffness due to excessive computer use, stress, posture, whiplash injuries, head and neck trauma etc., reduces blood supply to the brain causing all the symptoms of CFS.

Other causes of fatigue include low thyroid function, poor circulation, estrogen or testosterone deficiency, insomnia, low blood pressure, Vitamin D deficiency, anemia, fibromyalgia (inflamed, achy muscles), chronic sinuses (eye fatigue), osteoporosis, excessive sweating, depression, dehydration, diabetes, heart disease, excessive sexual activity, candida infection, and allergies.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.