Physicians are rewarded during their medical training for making diagnoses, particularly if the diagnosis is of a rare disorder. Unfortunately, the diagnosis—specifically, the disease label—may have undesirable consequences: the disease label categorizes a person as a patient, reducing their autonomy; the label legitimizes medical intervention that may or may not be beneficial; the disease label sanctions the “sick role,” with concomitant relief from social obligations, which may become an established behavior pattern; and “having a disease” classifies an individual as abnormal and may entail diminished employability or even deprivation of liberty by institutionalization. Multiple chemical sensitivity (MCS), an illness belief system manifested by culturally shaped illness behavior, raises questions regarding how symptoms become diseases of fashion, and the process seems to involve two phases: A genuine organic disease whose cause is challenging to detect and substantiate is appropriated as a template, and the template is broadcast to others who may have quite different symptoms but embrace the template as the explanation for their problems. Sympathetic physicians, patient support groups, and the media facilitate this broadcasting. Physicians who want to be patient advocates should encourage function, not impairment, and ability, not disability. The authors suggest that MCS is a form of illness behavior magnified by the medical model for care, not a consequence of underlying organ system dysfunction.