A term that is applied to several related syndromes characterized by ambiguous physical symptoms, suffering, and disability that are poorly explained and in which no specific illness or cause can by identified. These syndromes include: Multiple chemical sensitivity, the Sick Building Syndrome, repetition stress injury, the side effects of silicone breast implants, the Gulf War Syndrome, chronic whiplash, the Chronic Fatigue Syndrome, Fibromyalgia, cognitive difficulties, chronic widespread pain, Temporomandibular Disorder, Irritable Bowel Syndrome, lower back pain, tension headache, atypical facial pain, non-cardiac chest pain, insomnia, palpitation, non-ulcer dyspepsia, and dizziness. There often exists overlaps in symptoms or of the aforementioned syndromes themselves.

Pathophysiological causes may ultimately be found in some patients.  However, it is increasingly believed that these patients symptoms are amplified by psychosocial factors, psychosomatic causes, and a clinical approach that overemphasizes the biomedical and ignores the psychosocial and psychosomatic factors and causes.  Some doctors use this term to disguise the fact that they believe their patient’s symptoms are “all in their head.”