Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Chronic Fatigue Syndrome (CFS) ?
    ### Response:
    Despite a vigorous search, scientists have not yet identified what causes CFS. While a single cause for CFS may yet be identified, another possibility is that CFS has multiple causes. Conditions that have been studied to determine if they cause or trigger the development of CFS include infections, immune disorders, stress, trauma, and toxins.
    