CFS/ME does not have a single cause. It typically develops after a triggering event in a person with underlying biological vulnerabilities. Common triggers and contributing factors include:
Viral Infections
Epstein-Barr virus (EBV), cytomegalovirus (CMV), enteroviruses, HHV-6, and SARS-CoV-2 are among the most common infectious triggers. CFS/ME has been documented after many different viral infections, and the post-COVID pandemic has dramatically increased CFS prevalence worldwide.
Bacterial Infections
Lyme disease (Borrelia burgdorferi) and its co-infections are significant triggers for CFS. Many patients initially diagnosed with "post-treatment Lyme disease syndrome" meet full criteria for CFS/ME, suggesting shared underlying mechanisms.
Immune Dysfunction
Impaired natural killer cell function, shifted T-helper cell ratios, elevated pro-inflammatory cytokines, and mast cell activation are consistently found in CFS patients. The immune system appears stuck in a state of chronic, low-grade activation.
Mitochondrial Failure
Reduced ATP production, increased oxidative stress, and impaired mitochondrial membrane potential are hallmarks of CFS. The cells literally cannot produce enough energy to meet the body's demands, explaining the characteristic fatigue and post-exertional malaise.
Autonomic Dysfunction
Dysfunction of the autonomic nervous system -- which controls heart rate, blood pressure, digestion, and temperature -- is present in most CFS patients. This explains the orthostatic intolerance, POTS, and exercise intolerance commonly reported.
Gut Dysbiosis
Altered gut microbiome composition, increased intestinal permeability, and gut-brain axis disruption contribute to systemic inflammation, immune activation, and neurological symptoms. Gut health is increasingly recognized as central to CFS pathophysiology.