Potential role of stress and sensitization in the development and expression of multiple chemical sensitivity

Chemical sensitivity in humans may be an acquired disorder in which individuals become increasingly sensitive to chemicals in the environment. It is hypothesized that in individuals with multiple chemical sensitivity (MCS), a sensitization process has occurred that is akin to behavioral sensitization and kindling observed in rodents. In the rodent sensitization model, repeated exposure to stress or drugs of abuse enhances behavioral and neurochemical responses to subsequent stimuli (stress or drugs of abuse). Kindling is a form of sensitization in which repeated application of electrical stimuli applied to the brain at low levels culminates in the induction of full-blown seizures when the same stimulus is applied at a later time. A similar sensitization of specific limbic pathways in the brain may occur in individuals with MCS. The time-dependent nature of sensitization and kindling and the role of stress in the development of sensitization are discussed in the context of rodent models, with an emphasis on application of these models to human studies of MCS.