Chemical sensitivity has been recognized for an extended period. Over the last 30 years or more, there has been a growing number of chemicals to which humans are being exposed. Some people have become sensitive to one or more of these chemicals and present this sensitivity in a wide variety of signs or symptoms. Single or multiple organ systems may become involved. This article is intended to give an overview on the existence and recognition of chemical sensitivities and how they may be diagnosed and treated. The important item is to educate physicians to the existence of chemical sensitivity and to consider this in their differential diagnosis when the patient presents with the signs, symptoms, or clinical pattern that is explained.