the causes of chronic fatigue syndrome are not known . One theory is that it develops out of a combination of factors, such as viral infection, stress, and exposure to toxins. Chronic fatigue syndrome can run in families, so genetic factors may increase the risk of developing the disorder. The prevalence of chronic fatigue syndrome is higher among adults 30–39 years old than among those over 60 and women > men.
There is no specific test to detect it.so,it is difficult to diagnosed.Diagnosing chronic fatigue syndrome requires running many tests to rule-out other diseases and disorders that have similar symptoms. Making a diagnosis of chronic fatigue syndrome includes performing a complete evaluation that includes a medical history, including symptoms, and physical examination.