Many CFS patients have been found to have history of previous illnesses. Environmental factors like pollution and hygiene can also trigger CFS. 

Prolonged stress and depression are also likely to cause CFS. These two conditions are often triggered by emotional events and also because of hormonal imbalances. No study has been conducted yet to validate this hypothesis. However, experts advice to find ways to avoid stress and depression. This can positively impact CFS and also help avoid other complications.

A joint study report published by the CDC and Emory University, Atlanta in 2009 has found that people with CFS had faced high levels of childhood trauma as compared to people without CFS. It states that severe childhood traumas triggered by sexual abuse, emotional abuse and neglect were associated with a six-fold increase in CFS. Though, the overall effect of early life stress on CFS is still contested, experts suggest that these events alter the brain chemistry and make people more vulnerable to CFS as they grow older. 

CFS has been generally found to develop among 40-59 year old adults. In some cases, children and youngsters are also diagnosed with the disease. Young people are more likely to get cured of the illness if proper consultation with an expert is done early. 

It has been found that CFS patients have disturbed autonomic regulation of blood pressure and pulse which is also known as neurally mediated hypotension (NMH). It is triggered by worsening fatigue when patients stand for long periods or stay in warm places. However, these conditions are not universal. 

The absence of a balanced diet is responsible for many diseases. In case of CFS, there is no direct evidence to suggest the former plays a role in the development of CFS. However, doctors advice that balanced died is always beneficial to combat any chronic illness.

Studies have shown that a dysfunctional nervous system also plays an important role in CFS. Certain forms of emotional and physical stress alter the functioning of hypothalamic-pituitary-adrenal (HPA) axis. This alters the release of hormones like corticotrophin and cortisol which affects the immune and other body systems. It has been found that patients with CFS have low levels of cortisols. Researchers say that it is not directly responsible for symptoms of CFS but need more research to validate this assertion.

Scientists have proposed that certain immunologic dysfunctions may trigger CFS in different persons. However, no immune disorder has been found in patients with symptoms of CFS. Another hypothesis suggests that several events like viral infection or stress can trigger CFS. Patients with a history of allergies are also likely to develop this illness. 

Earlier, researchers almost agreed that CFS is caused by a mononucleosis epstein-barr virus (EBV). However, a study by the Centers for Disease Control and Prevention (CDC) in the US found no association of any single human pathogen with the illness. The study pointed that a lot many viruses or other pathogens may combine to cause a common endpoint, CFS in this case. Also, recently it has been found that infection with EBV, ross river virus and coxiella burnetti lead to a post-infective condition which meets the criteria for CFS in about 12 percent of cases.