NIH–Office of Research on Women’s Health

Chronic fatigue syndrome (CFS) is a debilitating and complex syndrome that involves multiple body systems. It is characterized by profound fatigue that is not improved by bed rest and may be exacerbated or re-kindled by physical or mental activity. Persons with CFS most often function at substantially lower levels of activity from their pre-onset capacities. In addition to these defining characteristics, a diverse array of other symptoms is associated with CFS; these symptoms include cognitive deficits, impaired sleep, myalgia, arthralgia, headache, gastrointestinal symptoms, and tender lymph nodes. Neither a specific cause(s) nor any specific diagnostic test(s) have been identified for this illness. The range of symptoms, however, suggests there may be subtle perturbations in multiple physiological pathways that are triggered by diverse causes such as infection, stress, brain structure abnormalities, hormone levels, proinflammatory cytokines, etc. Epidemiological evidence is also limited and requires further study. Existing data suggest, however, that CFS occurs three to four times more frequently among women than among men and 10 times more often in white Americans than in Americans of other racial/ethnic groups. A more recent study disputes these numbers and would narrow the gap between the sexes, as well as among racial/ethnic population subgroups. The cluster of symptoms we know as CFS has been described over the years under many names with varying definitions and suspected causes. But it was not until 1988 that a formal case definition emerged.