Clinical ecology is not a recognized medical specialty. Practitioners have been criticized for tricking mentally ill and suggestible patients into thinking that they were chemically sensitive. Twentieth century critics of clinical ecology charged that multiple chemical sensitivity (MCS) had never been clearly defined, no scientifically plausible mechanism has been proposed for it, no diagnostic tests have been substantiated, and not a single case has been scientifically proven. Well-conducted studies establishing the theories and practices of clinical ecology were not found in reviews of evidence supporting its practices by the American Medical Association in 1992, the American College of Physicians in 1989, the Canadian Psychiatric Association, the International Society of Regulatory Toxicology and Pharmacology in 1993, the American Academy of Allergy, Asthma and Immunology, and more recently by the American College of Occupational and Environmental Medicine in 1999.