Throughout history, when doctors and scientists have encountered illnesses that were not clearly visible and didn't have an obvious explanation, those illnesses have often been dismissed as either not real or as psychological. Asthma was among the illnesses once thought to be psychological. In order for doctors and researchers to reach similar conclusions about multiple chemical sensitivity, they have had to overlook a great deal of valuable evidence including the signs and symptoms of patients as well as the commonalities this illness shares with other now well-recognized hypersensitivity illnesses. Researching the relationship between multiple chemical sensitivity and other hypersensitivity illnesses may help narrow down the potential mechanisms in this illness and bring answers to patients, which might ease the burden of having an illness that is once again unrecognized by the people patients are most dependent on for help.