Untoward reactions to environmental chemicals, particularly when a subject reports difficulties with exposures to chemicals of diverse classes involving more than one organ system, have been poorly understood and an area of great controversy. Studies of airway inflammation induced by respiratory irritants have established neurogenic inflammation as the mechanism for irritant asthma and rhinitis. Remodeling of the airway after an acute irritant exposure can lead to a heightened sensitivity to irritants that persists. Recognition that rhinitis, while sometimes regarded as a trivial disease,...