Respiratory irritants encountered at work.

Respiratory irritants cause acute lung injury. Their effects are distinguished from hypersensitivity induced lung injury by their mechanism of action a direct toxic effect and the speed of onset within minutes or hours rather than months or years. Respiratory irritants may be inhaled or transported to the lungs by the circulation. This article focuses on the long term consequences of inhaled respiratory irritants on the airways. Inhaled respiratory irritants provoke an acute inflammatory response with injury to the epithelial cells of the lungs. Depending on the site of uptake or deposition of the irritant, these effects predominantly involve the upper respiratory tract and airways or the gas exchanging parts of the lungs (fig 1). Irritants may be inhaled as gases or vapours, solid particles, or liquid aerosols. In general, water soluble gases and vapours and particles of aerodynamic diameter greater than 5,m are deposited in the upper respiratory tract and proximal airways. Water insoluble gases, vapours and fumes, and particles whose aerodynamic diameter is 05-5,m can penetrate into and be deposited or taken up in peripheral airways and the gas exchanging parts ofthe lung. Irritants deposited or dissolved in the upper respiratory tract and proximal airways may cause injury to airway mucosal cells, exaggerated physiological responses, an acute inflammatory reaction, or all three of these. Exaggerated physiological responses include cough (from stimulation of