Evidence linking psychological stress to the expression of asthma and atopy continues to grow. Examining the underlying molecular mechanisms linking stress to asthma and other allergic phenomena is an active area of research. Evidence is reviewed for the influence of stress on neuroimmunoregulation and oxidative stress pathways, which, in turn, may affect biological hypersensitivity to environmental stimuli characteristic of atopic disorders. Critical periods of development, including in utero environment, are underscored. The role of genetics and gene-by-environment interactions is also discussed.